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[1]  arXiv:1709.06993 [pdf]
Title: The PICARD Payload Data Centre
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

PICARD is a scientific space mission dedicated to the study of the solar variability origin. A French micro-satellite will carry an imaging telescope for measuring the solar diameter, limb shape and solar oscillations, and two radiometers for measuring the total solar irradiance and the irradiance in five spectral domains, from ultraviolet to infrared. The mission is planed to be launched in 2009 for a 3-year duration. This article presents the PICARD Payload Data Centre, which role is to collect, process and distribute the PICARD data. The Payload Data Centre is a joint project between laboratories, space agency and industries. The Belgian scientific policy office funds the industrial development and future operations under the European Space Agency program. The development is achieved by the SPACEBEL Company. The Belgian operation centre is in charge of operating the PICARD Payload Data Centre. The French space agency leads the development in partnership with the French scientific research centre, which is responsible for providing all the scientific algorithms. The architecture of the PICARD Payload Data Centre (software and hardware) is presented. The software system is based on a Service Oriented Architecture. The host structure is made up of the basic functions such as data management, task scheduling and system supervision including a graphical interface used by the operator to interact with the system. The other functions are mission-specific: data exchange (acquisition, distribution), data processing (scientific and non-scientific processing) and managing the payload (programming, monitoring). The PICARD Payload Data Centre is planned to be operated for 5 years. All the data will be stored into a specific data centre after this period.

[2]  arXiv:1709.06999 [pdf, other]
Title: GALARIO: a GPU Accelerated Library for Analysing Radio Interferometer Observations
Comments: 13 pages, 9 figures. Submitted to MNRAS. Code at this https URL and documentation at this https URL
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

We present GALARIO, a computational library that exploits the power of modern graphical processing units (GPUs) to accelerate the analysis of observations from radio interferometers like ALMA or Jansky VLA. GALARIO speeds up the computation of synthetic visibilities from a generic 2D model image or a radial brightness profile (for axisymmetric sources). On a GPU, GALARIO is 150 faster than standard Python and 10 times faster than serial C++ code on a CPU. Highly modular, easy to use and to adopt in existing code, GALARIO comes as two compiled libraries, one for Nvidia GPUs and one for multicore CPUs, where both have the same functions with identical interfaces. GALARIO comes with Python bindings but can also be directly used in C or C++. The versatility and the speed of GALARIO open new analysis pathways that otherwise would be prohibitively time consuming, e.g. fitting high resolution observations of large number of objects, or entire spectral cubes of molecular gas emission. It is a general tool that can be applied to any field that uses radio interferometer observations. The source code is available online at https://github.com/mtazzari/galario under the open source GNU Lesser General Public License v3.

[3]  arXiv:1709.07000 [pdf, ps, other]
Title: Chemical enrichment and accretion of nitrogen-loud quasars
Comments: 11 pages, 7 figures, accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present rest-frame optical spectra of 12 nitrogen-loud quasars at z ~ 2.2, whose rest-frame ultraviolet (UV) spectra show strong nitrogen broad emission lines. To investigate their narrow-line region (NLR) metallicities, we measure the equivalent width (EW) of the [OIII]5007 emission line: if the NLR metallicity is remarkably high as suggested by strong UV nitrogen lines, the [OIII]5007 line flux should be very week due to the low equilibrium temperature of the ionized gas owing to significant metal cooling. In the result, we found that our spectra show moderate EW of the [OIII]5007 line similar to general quasars. This indicates nitrogen-loud quasars do not have extremely metal-rich gas clouds in NLRs. This suggests that strong nitrogen lines from broad-line regions (BLRs) are originated by exceptionally high abundances of nitrogen relative to oxygen without very high BLR metallicities. This result indicates that broad-emission lines of nitrogen are not good indicators of the BLR metallicity in some cases. On the other hand, we also investigate virial black-hole masses and Eddington ratios by using the Hbeta and CIV1549 lines for our sample. As a result, we found that black-hole masses and Eddington ratios of nitrogen-loud quasars tend to be low and high relative to normal quasars, suggesting that nitrogen-loud quasars seem to be in a rapidly-accreting phase. This can be explained in terms of a positive correlation between Eddington ratios and nitrogen abundances of quasars, that is probably caused by the connection between the mass accretion onto black holes and nuclear star formation.

[4]  arXiv:1709.07003 [pdf, other]
Title: Low Metallicities and Old Ages for Three Ultra-Diffuse Galaxies in the Coma Cluster
Subjects: Astrophysics of Galaxies (astro-ph.GA)

A large population of ultra-diffuse galaxies (UDGs) was recently discovered in the Coma cluster. Here we present optical spectra of three such UDGs, DF7, DF44 and DF17, which have central surface brightnesses of $\mu_g \approx 24.4-25.1$ mag arcsec$^{-2}$. The spectra were acquired as part of an ancillary program within the SDSS-IV MaNGA Survey. We stacked 19 fibers in the central regions from larger integral field units (IFUs) per source. With over 13.5 hours of on-source integration we achieved a mean signal-to-noise ratio (S/N) in the optical of $9.5$\AA$^{-1}$, $7.9$\AA$^{-1}$ and $5.0$\AA$^{-1}$, respectively, for DF7, DF44 and DF17. Stellar population models applied to these spectra enable measurements of recession velocities, ages and metallicities. The recession velocities of DF7, DF44 and DF17 are $6599^{+40}_{-25}$km/s, $6402^{+41}_{-39}$km/s and $8315^{+43}_{-43}$km/s, spectroscopically confirming that all of them reside in the Coma cluster. The stellar populations of these three galaxies are old and metal-poor, with ages of $7.9^{+3.6}_{-2.5}$Gyr, $8.9^{+4.3}_{-3.3}$Gyr and $9.1^{+3.9}_{-5.5}$Gyr, and iron abundances of $\mathrm{[Fe/H]}$ $-1.0^{+0.3}_{-0.4}$, $-1.3^{+0.4}_{-0.4}$ and $-0.8^{+0.5}_{-0.5}$, respectively. Their stellar masses are $3$-$6\times10^8 M_\odot$. The UDGs in our sample are as old or older than galaxies at similar stellar mass or velocity dispersion (only DF44 has an independently measured dispersion). They all follow the well-established stellar mass$-$stellar metallicity relation, while DF44 lies below the velocity dispersion-metallicity relation. These results, combined with the fact that UDGs are unusually large for their stellar mass, suggest that stellar mass plays a more important role in setting stellar population properties for these galaxies than either size or surface brightness.

[5]  arXiv:1709.07004 [pdf, ps, other]
Title: White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Linewidths: Kepler Observations of 27 Pulsating DA White Dwarfs Through K2 Campaign 8
Comments: 33 pages, 31 figures, 5 tables; accepted for publication in ApJS. All raw and reduced data are collected at this http URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present photometry and spectroscopy for 27 pulsating hydrogen-atmosphere white dwarfs (DAVs, a.k.a. ZZ Ceti stars) observed by the Kepler space telescope up to K2 Campaign 8, an extensive compilation of observations with unprecedented duration (>75 days) and duty cycle (>90%). The space-based photometry reveals pulsation properties previously inaccessible to ground-based observations. We observe a sharp dichotomy in oscillation mode linewidths at roughly 800 s, such that white dwarf pulsations with periods exceeding 800 s have substantially broader mode linewidths, more reminiscent of a damped harmonic oscillator than a heat-driven pulsator. Extended Kepler coverage also permits extensive mode identification: We identify the spherical degree of 61 out of 154 unique radial orders, providing direct constraints of the rotation period for 20 of these 27 DAVs, more than doubling the number of white dwarfs with rotation periods determined via asteroseismology. We also obtain spectroscopy from 4m-class telescopes for all DAVs with Kepler photometry. Using these homogeneously analyzed spectra we estimate the overall mass of all 27 DAVs, which allows us to measure white dwarf rotation as a function of mass, constraining the endpoints of angular momentum in low- and intermediate-mass stars. We find that 0.51-to-0.73-solar-mass white dwarfs, which evolved from 1.7-to-3.0-solar-mass ZAMS progenitors, have a mean rotation period of 35 hr with a standard deviation of 28 hr, with notable exceptions for higher-mass white dwarfs. Finally, we announce an online repository for our Kepler data and follow-up spectroscopy, which we collect at this http URL

[6]  arXiv:1709.07006 [pdf, other]
Title: Simulations of the Fomalhaut System Within Its Local Galactic Environment
Comments: Accepted to MNRAS, 22 pages, 15 figures, 2 appendices
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Fomalhaut A is among the most well-studied nearby stars and has been discovered to possess a putative planetary object as well as a remarkable eccentric dust belt. This eccentric dust belt has often been interpreted as the dynamical signature of one or more planets that elude direct detection. However, the system also contains two other stellar companions residing ~100,000 AU from Fomalhaut A. We have designed a new symplectic integration algorithm to model the evolution of Fomalhaut A's planetary dust belt in concert with the dynamical evolution of its stellar companions to determine if these companions are likely to have generated the dust belt's morphology. Using our numerical simulations, we find that close encounters between Fomalhaut A and B are expected, with a ~25% probability that the two stars have passed within at least 400 AU of each other at some point. Although the outcomes of such encounter histories are extremely varied, these close encounters nearly always excite the eccentricity of Fomalhaut A's dust belt and occasionally yield morphologies very similar to the observed belt. With these results, we argue that close encounters with Fomalhaut A's stellar companions should be considered a plausible mechanism to explain its eccentric belt, especially in the absence of detected planets capable of sculpting the belt's morphology. More broadly, we can also conclude from this work that very wide binary stars may often generate asymmetries in the stellar debris disks they host.

[7]  arXiv:1709.07007 [pdf, other]
Title: A Vorticity-Preserving Hydrodynamical Scheme for Modeling Accretion Disk Flows
Comments: Accepted by ApJ; 14 pages, 8 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Vortices, turbulence, and unsteady non-laminar flows are likely both prominent and dynamically important features of astrophysical disks. Such strongly nonlinear phenomena are often difficult, however, to simulate accurately, and are generally amenable to analytic treatment only in idealized form. In this paper, we explore the evolution of compressible two-dimensional flows using an implicit dual-time hydrodynamical scheme that strictly conserves vorticity (if applied to simulate inviscid flows for which Kelvin's Circulation Theorem is applicable). The algorithm is based on the work of Lerat, Falissard & Side (2007), who proposed it in the context of terrestrial applications such as the blade-vortex interactions generated by helicopter rotors. We present several tests of Lerat et al.'s vorticity-preserving approach, which we have implemented to second-order accuracy, providing side-by-side comparisons with other algorithms that are frequently used in protostellar disk simulations. The comparison codes include one based on explicit, second-order van-Leer advection, one based on spectral methods, and another that implements a higher-order Godunov solver. Our results suggest that Lerat et al's algorithm will be useful for simulations of astrophysical environments in which vortices play a dynamical role, and where strong shocks are not expected.

[8]  arXiv:1709.07008 [pdf, other]
Title: Modeling $237$ Lyman-$α$ spectra of the MUSE-Wide survey
Authors: Max Gronke
Comments: 10 pages, 7 figures; data can be downloaded at this http URL
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We compare $237$ Lyman-$\alpha$ (Ly$\alpha$) spectra of the "MUSE-Wide survey" (Herenz et al. 2017) to a suite of radiative transfer simulations consisting of a central luminous source within a concentric, moving shell of neutral gas, and dust. This six parameter shell-model has been used numerously in previous studies, however, on significantly smaller data-sets. We find that the shell-model can reproduce the observed spectral shape very well - better than the also common `Gaussian-minus-Gaussian' model which we also fitted to the dataset. Specifically, we find that $\sim 94\%$ of the fits possess a goodness-of-fit value of $p(\chi^2)>0.1$. The large number of spectra allows us to robustly characterize the shell-model parameter range, and consequently, the spectral shapes typical for realistic spectra. We find that the vast majority of the Ly$\alpha$ spectral shapes require an outflow and only $\sim 5\%$ are well-fitted through an inflowing shell. In addition, we find $\sim 46\%$ of the spectra to be consistent with a neutral hydrogen column density $<10^{17}\,\mathrm{cm}^{-2}$ - suggestive of a non-negligible fraction of continuum leakers in the MUSE-Wide sample. Furthermore, we correlate the spectral against the Ly$\alpha$ halo properties against each other but do not find any strong correlation.

[9]  arXiv:1709.07009 [pdf, ps, other]
Title: Galaxy evolution in protoclusters
Comments: 14 pages, 9 figures, accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We investigate galaxy evolution in protoclusters using a semi-analytic model applied to the Millennium Simulation, scaled to a Planck cosmology. We show that the model reproduces the observed behaviour of the star formation history (SFH) both in protoclusters and the field. The rate of star formation peaks $\sim0.7\,{\rm Gyr}$ earlier in protoclusters than in the field and declines more rapidly afterwards. This results in protocluster galaxies forming significantly earlier: 80% of their stellar mass is already formed by $z=1.4$, but only 45% of the field stellar mass has formed by this time. The model predicts that field and protocluster galaxies have similar average specific star-formation rates (sSFR) at $z>3$, and we find evidence of an enhancement of star formation in the dense protoclusters at early times. At $z<3$, protoclusters have lower sSFRs, resulting in the disparity between the SFHs. We show that the stellar mass functions of protoclusters are top-heavy compared with the field due to the early formation of massive galaxies, and the disruption and merging of low-mass satellite galaxies in the main haloes. The fundamental cause of the different SFHs and mass functions is that dark matter haloes are biased tracers of the dark matter density field: the high density of haloes and the top-heavy halo mass function in protoclusters result in the early formation then rapid merging and quenching of galaxies. We compare our results with observations from the literature, and highlight which observables provide the most informative tests of galaxy formation.

[10]  arXiv:1709.07010 [pdf, other]
Title: KELT-19Ab: A P~4.6 Day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion
Comments: Submitted to AAS Journals. 16 pages, 13 figures, 6 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We present the discovery of the giant planet KELT-19Ab, which transits the moderately bright ($V \sim 9.9$) A8V star TYC 764-1494-1. We confirm the planetary nature of the companion via a combination of low-precision radial velocities, which limit the mass to $M_{\rm P} < 4.1\,M_{\rm J}$ ($3\sigma$), and a clear Doppler tomography signal, which indicates a retrograde projected spin-orbit misalignment of $\lambda = -179.7^{+3.7}_{-3.8}$ degrees. Global modeling indicates that the $T_{\rm eff} =7500 \pm 110\,\rm K$ host star has $M_* = 1.62^{+0.25}_{-0.20}\,M_{\odot}$ and $R_* = 1.83 \pm 0.10\,R_{\odot}$. The planet has a radius of $R_{\rm P}=1.91 \pm 0.11\,R_{\rm J}$ and receives a stellar insolation flux of $\sim 3.2\times 10^{9}\,{\rm\,erg\,s^{-1}\,cm^{-2}}$, leading to an inferred equilibrium temperature of $T_{\rm eq} \sim 1935\,\rm K$ assuming zero albedo and complete heat redistribution. With a $v\sin{I_*}=84.8\pm 2.0\,\rm km\,s^{-1}$, the host star is rapidly-rotating. Interestingly, its $v\sin{I_*}$ is relatively low compared to other stars with similar effective temperatures, and it appears to be enhanced in metallic species such as strontium but deficient in others such as calcium, suggesting that it is likely an Am star. KELT-19A would be the first definitive detection of an Am host of a transiting planet of which we are aware. Adaptive optics observations of the system reveal the existence of a companion with late G9V/early K1V spectral type at a projected separation of $\approx 160\, \mathrm{AU}$. Radial velocity measurements indicate that this companion is bound. Most Am stars are known to have stellar companions, which are often invoked to explain the relatively slow rotation of the primary. In this case, the stellar companion is unlikely to have caused the tidal braking of the primary.

[11]  arXiv:1709.07011 [pdf, other]
Title: Modeling the Infrared Reverberation Response of the Circumnuclear Dusty Torus in AGN: The Effects of Cloud Orientation and Anisotropic Illumination
Comments: 17 pages, 14 figures, published in the Astrophysical Journal (2017 July 1)
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The obscuring circumnuclear torus of dusty molecular gas is one of the major components of active galactic nuclei (AGN). The torus can be studied by analyzing the time response of its infrared (IR) dust emission to variations in the AGN continuum luminosity, a technique known as reverberation mapping. The IR response is the convolution of the AGN ultraviolet/optical light curve with a transfer function that contains information about the size, geometry, and structure of the torus. Here, we describe a new computer model that simulates the reverberation response of a clumpy torus. Given an input optical light curve, the code computes the emission of a 3D ensemble of dust clouds as a function of time at selected IR wavelengths, taking into account light travel delays. We present simulated dust emission responses at 3.6, 4.5, and 30 $\mu$m that explore the effects of various geometrical and structural properties, dust cloud orientation, and anisotropy of the illuminating radiation field. We also briefly explore the effects of cloud shadowing (clouds are shielded from the AGN continuum source). Example synthetic light curves have also been generated, using the observed optical light curve of the Seyfert 1 galaxy NGC 6418 as the input. The torus response is strongly wavelength-dependent, due to the gradient in cloud surface temperature within the torus, and because the cloud emission is strongly anisotropic at shorter wavelengths. Anisotropic illumination of the torus also significantly modifies the torus response, reducing the lag between the IR and optical variations.

[12]  arXiv:1709.07012 [pdf, ps, other]
Title: On the formation mechanisms of compact elliptical galaxies
Comments: Accepeted for publication in MNRAS. 24 pages, 21 figures, 5 tables
Subjects: Astrophysics of Galaxies (astro-ph.GA)

In order to investigate the formation mechanisms of the rare compact elliptical galaxies (cE) we have compiled a sample of 25 cEs with good SDSS spectra, covering a range of stellar masses, sizes and environments. They have been visually classified according to the interaction with their host, representing different evolutionary stages. We have included clearly disrupted galaxies, galaxies that despite not showing signs of interaction are located close to a massive neighbor (thus are good candidates for a stripping process), and cEs with no host nearby. For the latter, tidal stripping is less likely to have happened and instead they could simply represent the very low-mass, faint end of the ellipticals. We study a set of properties (structural parameters, stellar populations, star formation histories and mass ratios) that can be used to discriminate between an intrinsic or stripped origin. We find that one diagnostic tool alone is inconclusive for the majority of objects. However, if we combine all the tools a clear picture emerges. The most plausible origin, as well as the evolutionary stage and progenitor type, can be then determined. Our results favor the stripping mechanism for those galaxies in groups and clusters that have a plausible host nearby, but favors an intrinsic origin for those rare cEs without a plausible host and that are located in looser environments.

[13]  arXiv:1709.07015 [pdf, other]
Title: Star Formation Quenching in Green Valley Galaxies at $0.5\lesssim z\lesssim1.0$ and Constraints with Galaxy Morphologies
Comments: 14 pages, 9 figures, 1 table. Accepted for publication in MNRAS (14 Sep. 2017)
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We calculate the star formation quenching timescales in green valley galaxies at intermediate redshifts ($z\sim0.5-1$) using stacked zCOSMOS spectra of different galaxy morphological types: spheroidal, disk-like, irregular and merger, dividing disk-like galaxies further into unbarred, weakly-barred and strongly-barred, assuming a simple exponentially-decaying star formation history model and based on the H$_{\delta}$ absorption feature and the $4000$ \AA ~break. We find that different morphological types present different star formation quenching timescales, reinforcing the idea that the galaxy morphology is strongly correlated with the physical processes responsible for quenching star formation. Our quantification of the star formation quenching timescale indicates that disks have typical timescales $60\%$ to 5 times longer than that of galaxies presenting spheroidal, irregular or merger morphologies. Barred galaxies in particular present the slowest transition timescales through the green valley. This suggests that although secular evolution may ultimately lead to gas exhaustion in the host galaxy via bar-induced gas inflows that trigger star formation activity, secular agents are not major contributors in the rapid quenching of galaxies at these redshifts. Galaxy interaction, associated with the elliptical, irregular and merger morphologies contribute, to a more significant degree, to the fast transition through the green valley at these redshifts. In the light of previous works suggesting that both secular and merger processes are responsible for the star formation quenching at low redshifts, our results provide an explanation to the recent findings that star formation quenching happened at a faster pace at $z\sim0.8$.

[14]  arXiv:1709.07018 [pdf, ps, other]
Title: NuSTAR hard X-ray data and Gemini 3D spectra reveal powerful AGN and outflow histories in two low-redshift Lyman-$α$ blobs
Comments: 15 pages, 17 Figures, accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We have shown that Lyman-$\alpha$ blobs (LABs) may still exist even at $z\sim0.3$, about 7 billion years later than most other LABs known (Schirmer et al. 2016). Their luminous Ly$\alpha$ and [OIII] emitters at $z\sim0.3$ offer new insights into the ionization mechanism. This paper focuses on the two X-ray brightest LABs at $z\sim0.3$, SDSS J0113$+$0106 (J0113) and SDSS J1155$-$0147 (J1155), comparable in size and luminosity to `B1', one of the best-studied LABs at $z \gtrsim$ 2. Our NuSTAR hard X-ray (3--30 keV) observations reveal powerful active galactic nuclei (AGN) with $L_{2-10{\;\rm keV}}=(0.5$--$3)\times10^{44}$ erg cm$^{-2}$ s$^{-1}$. J0113 also faded by a factor of $\sim 5$ between 2014 and 2016, emphasizing that variable AGN may cause apparent ionization deficits in LABs. Joint spectral analyses including Chandra data constrain column densities of $N_{\rm H}=5.1^{+3.1}_{-3.3}\times10^{23}$ cm$^{-2}$ (J0113) and $N_{\rm H}=6.0^{+1.4}_{-1.1}\times10^{22}$ cm$^{-2}$ (J1155). J0113 is likely buried in a torus with a narrow ionization cone, but ionizing radiation is also leaking in other directions as revealed by our Gemini/GMOS 3D spectroscopy. The latter shows a bipolar outflow over $10$ kpc, with a peculiar velocity profile that is best explained by AGN flickering. X-ray analysis of J1155 reveals a weakly absorbed AGN that may ionize over a wide solid angle, consistent with our 3D spectra. Extinction corrected [OIII] log-luminosities are high, $\sim43.6$. The velocity dispersions are low, $\sim100$--$150$ km s$^{-1}$, even at the AGN positions. We argue that this is a combination of high extinction hiding the turbulent gas, and previous outflows that have cleared the escape paths for their successors.

[15]  arXiv:1709.07026 [pdf, other]
Title: Electron Heating and Saturation of Self-regulating Magnetorotational Instability in Protoplanetary Disks
Comments: 12 pages, 12 figures, accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Magnetorotational instability (MRI) has a potential to generate the vigorous turbulence in protoplanetary disks, although its turbulence strength and accretion stress remains debatable because of the uncertainty of MRI with low ionization fraction. We focus on the heating of electrons by strong electric fields which amplifies nonideal magnetohydrodynamic effects. The heated electrons frequently collide with and stick to dust grains, which in turn decreases the ionization fraction and is expected to weaken the turbulent motion driven by MRI. In order to quantitatively investigate the nonlinear evolution of MRI including the electron heating, we perform magnetohydrodynamical simulation with the unstratified shearing box. We introduce a simple analytic resistivity model depending on the current density by mimicking resistivity given by the calculation of ionization. Our simulation confirms that the electron heating suppresses magnetic turbulence when the electron heating occurs with low current density. We find a clear correlation between magnetic stress and its current density, which means that the magnetic stress is proportional to the squared current density. When the turbulent motion is completely suppressed, laminar accretion flow is caused by ordered magnetic field. We give an analytical description of the laminar state by using a solution of linear perturbation equations with resistivity. We also propose a formula that successfully predicts the accretion stress in the presence of the electron heating.

[16]  arXiv:1709.07030 [pdf, other]
Title: Multiple origins for the DLA at $z_\mathrm{abs}=0.313$ toward PKS 1127$-$145 indicated by a complex dust depletion pattern of Ca, Ti, and Mn
Comments: 10 pages, 8 figures, accepted for A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We investigate the dust depletion properties of optically thick gas in and around galaxies and its origin we study in detail the dust depletion patterns of Ti, Mn, and Ca in the multi-component damped Lyman-$\alpha$ (DLA) absorber at $z_\mathrm{abs}=0.313$ toward the quasar PKS 1127$-$145.} We performed a detailed spectral analysis of the absorption profiles of CaII, MnII, TiII, and NaI associated with the DLA toward PKS 1127$-$145, based on optical high-resolution data obtained with the UVES instrument at the Very Large Telescope (VLT). We obtained column densities and Doppler-parameters for the ions listed above and determine their gas-phase abundances, from which we conclude on their dust depletion properties. We compared the Ca and Ti depletion properties of this DLA with that of other DLAs. One of the six analyzed absorption components shows a striking underabundance of Ti and Mn in the gas-phase, indicating the effect of dust depletion for these elements and a locally enhanced dust-to-gas ratio. In this DLA and in other similar absorbers, the MnII abundance follows that of TiII very closely, implying that both ions are equally sensitive to the dust depletion effects. Our analysis indicates that the DLA toward PKS 1127$-$145 has multiple origins. With its narrow line width and its strong dust depletion, component 3 points toward the presence of a neutral gas disk from a faint LSB galaxy in front of PKS 1127$-$145, while the other, more diffuse and dust-poor, absorption components possibly are related to tidal gas features from the interaction between the various, optically confirmed galaxy-group members. In general, the Mn/CaII ratio in sub-DLAs and DLAs possibly serves as an important indicator to discriminate between dust-rich and dust-poor in neutral gas in and around galaxies.

[17]  arXiv:1709.07034 [pdf, other]
Title: Cooling of Accretion-Heated Neutron Stars
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan. In case of missing sources and/or references in the tables, please contact the first author and they will be included in updated versions of this review
Journal-ref: J. Astrophys. Astr. (September 2017) 38:49
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present a brief, observational review about the study of the cooling behaviour of accretion-heated neutron stars and the inferences about the neutron-star crust and core that have been obtained from these studies. Accretion of matter during outbursts can heat the crust out of thermal equilibrium with the core and after the accretion episodes are over, the crust will cool down until crust-core equilibrium is restored. We discuss the observed properties of the crust cooling sources and what has been learned about the physics of neutron-star crusts. We also briefly discuss those systems that have been observed long after their outbursts were over, i.e, during times when the crust and core are expected to be in thermal equilibrium. The surface temperature is then a direct probe for the core temperature. By comparing the expected temperatures based on estimates of the accretion history of the targets with the observed ones, the physics of neutron-star cores can be investigated. Finally, we discuss similar studies performed for strongly magnetized neutron stars in which the magnetic field might play an important role in the heating and cooling of the neutron stars.

[18]  arXiv:1709.07040 [pdf, ps, other]
Title: Phase transition in compact stars: nucleation mechanism and $γ$-ray bursts revisited
Comments: 19 pages, 7 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)

We have revisited the nucleation process based on the Lifshitz-Kagan theory, which is the underlying mechanism of conversion of a pulsar constituted of hadronic matter to a quark star. We have selected appropriate models that have been tested against experimental and observational constraints to restrict the model arbitrariness present in previous investigations. The phase transition pressures and chemical potentials have been identified and afterwards, the tunneling probabilities and the nucleation time were computed. The critical pressures for which the half life of the metastable hadronic phase is one year were obtained. Even with the restrictions imposed to the selection of models, the results remained model dependent, but we found that the tunneling that makes possible the appearance of stable matter requires an overpressure that is practically independent of the quark matter bag constant. Finally, we have confirmed that the nucleation process can be one of the causes of gamma-ray bursts.

[19]  arXiv:1709.07044 [pdf]
Title: Sustaining ALMA Science Through 2030 A North American Perspective
Comments: 2 pages, submitted to National Radio Science Meeting (NRSM) 4-7 Jan 2017, Boulder Colorado
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

ALMA will sustain its transformational science through 2030 via an aggressive series of upgrades, for which an overview is provided.

[20]  arXiv:1709.07049 [pdf, other]
Title: Gravitational waves from single neutron stars: an advanced detector era survey
Comments: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and Astrophysics of Neutron Stars", NewCompStar COST Action 1304
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc)

With the doors beginning to swing open on the new gravitational wave astronomy, this review provides an up-to-date survey of the most important physical mechanisms that could lead to emission of potentially detectable gravitational radiation from isolated and accreting neutron stars. In particular we discuss the gravitational wave-driven instability and asteroseismology formalism of the f- and r-modes, the different ways that a neutron star could form and sustain a non-axisymmetric quadrupolar "mountain" deformation, the excitation of oscillations during magnetar flares and the possible gravitational wave signature of pulsar glitches. We focus on progress made in the recent years in each topic, make a fresh assessment of the gravitational wave detectability of each mechanism and, finally, highlight key problems and desiderata for future work.

[21]  arXiv:1709.07069 [pdf, ps, other]
Title: Relativistic disc line: a tool to constrain neutron star equation of state models
Authors: Sudip Bhattacharyya (TIFR, India)
Comments: 10 pages, 10 figures, Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan
Journal-ref: 2017, JApA, 38, 38
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)

Relativistic iron K$\alpha$ spectral emission line from the inner disc of a neutron star low-mass X-ray binary (LMXB) was first detected in 2007. This discovery opened up new ways to probe strong gravity and dense matter. The past decade has seen detections of such a line from many neutron star LMXBs, and confirmation of this line from the same source with several X-ray satellites. These have firmly established the new field of relativistic disc line from neutron star systems in only ten years. Fitting the shape of such a line with an appropriate general relativistic model provides the accretion disc inner edge radius to the stellar mass ratio. In this review, we briefly discuss how an accurate measurement of this ratio with a future larger area X-ray instrument can be used to constrain neutron star equation of state models.

[22]  arXiv:1709.07070 [pdf, other]
Title: Accretion of Planetary Material onto Host Stars
Comments: 18 pages, 5 figures (with some redacted), invited review
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Accretion of planetary material onto host stars may occur throughout a star's life. Especially prone to accretion, extrasolar planets in short-period orbits, while relatively rare, constitute a significant fraction of the known population, and these planets are subject to dynamical and atmospheric influences that can drive significant mass loss. Theoretical models frame expectations regarding the rates and extent of this planetary accretion. For instance, tidal interactions between planets and stars may drive complete orbital decay during the main sequence. Many planets that survive their stars' main sequence lifetime will still be engulfed when the host stars become red giant stars. There is some observational evidence supporting these predictions, such as a dearth of close-in planets around fast stellar rotators, which is consistent with tidal spin-up and planet accretion. There remains no clear chemical evidence for pollution of the atmospheres of main sequence or red giant stars by planetary materials, but a wealth of evidence points to active accretion by white dwarfs. In this article, we review the current understanding of accretion of planetary material, from the pre- to the post-main sequence and beyond. The review begins with the astrophysical framework for that process and then considers accretion during various phases of a host star's life, during which the details of accretion vary, and the observational evidence for accretion during these phases.

[23]  arXiv:1709.07074 [pdf]
Title: Etude et mise en oeuvre des techniques Temps-Distance en Heliosismologie
Comments: Master's thesis (2006), University of Sciences and Technology Houari Boumediene, Algeria. in French
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In the same way that seismologists study the interior of the earth from the waves generated by earthquakes, heliosismology is the science that is interested in the study of oscillatory waves inside the Sun. Temperature, chemical composition, rotational velocities at different depths are all factors that influence the oscillation frequencies of the waves trapped inside the Sun. The observation and measurement of the frequencies (or velocities) of oscillations of the principal modes on the surface of the Sun allow us to study the internal properties of the star. In our study, we use a local helioseismic method, called "Time-Distance"; the latter, after appropriate treatment (remapping, tracking, and filtering) of the data, which carried out from the GONG (Global Oscillation Network Group) observation network, allows us to deduce, by correlation of the observed signals, the relationship between the time of the wave path and its crossed distance (hence the name of the method) between different points on the surface as a function of the different solar sub-surface parameters, via the dispersion relation. Once the travel times have been established by approximation of the correlation function by a Gaussian wave packet and based on the Fermat principle dealing with acoustic waves, we find the relationship between these times and the internal parameters of the crossed medium. Two models are considered in this study. The first does not include the effects of the magnetic field and takes into account the flow velocity and the sound speed. The second, on the other hand, includes the magnetic effects, by means of the Alfven velocity (magnetic field perturbation velocity), in addition to the parameters mentioned above. The last part of this paper was devoted to the inversion of the obtained times, which allows us to go back to the solar internal parameters.

[24]  arXiv:1709.07076 [pdf, ps, other]
Title: Rayleigh scattering in dense fluid helium
Comments: Accepted for publication in MNRAS; 14 pages, 14 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Iglesias et al. (2002) showed that the Rayleigh scattering from helium atoms decreases by collective effects in the atmospheres of cool white dwarf stars. Their study is here extended to consider an accurate evaluation of the atomic polarizability and the density effects involved in the Rayleigh cross section over a wide density-temperature region. The dynamic dipole polarizability of helium atoms in the ground state is determinated with the oscillator-strength distribution approach. The spectral density of oscillator strength considered includes most significant single and doubly excited transitions to discrete and continuum energies. Static and dynamic polarizability results are confronted with experiments and other theoretical evaluations shown a very good agreement. In addition, the refractive index of helium is evaluated with the Lorentz-Lorenz equation and shows a satisfactory agreement with the most recent experiments. The effect of spatial correlation of atoms on the Rayleigh scattering is calculated with Monte Carlo simulations and effective energy potentials that represent the particle interactions, covering fluid densities between 0.005 and a few g/cm$^3$ and temperatures between $1000$ K and $15000$ K. We provide analytical fits from which the Rayleigh cross section of fluid helium can be easily calculated at wavelength $\lambda>505.35$ \AA. Collision-induced light scattering was estimated to be the dominant scattering process at densities greater than 1-2 g/cm$^3$ depending on the temperature.

[25]  arXiv:1709.07099 [pdf, other]
Title: Emulating galaxy clustering and galaxy-galaxy lensing into the deeply nonlinear regime: methodology, information, and forecasts
Comments: 23 pages, 7 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The combination of galaxy-galaxy lensing (GGL) with galaxy clustering is one of the most promising routes to determining the amplitude of matter clustering at low redshifts. We show that extending clustering+GGL analyses from the linear regime down to $\sim 0.5 \, h^{-1}$ Mpc scales increases their constraining power considerably, even after marginalizing over a flexible model of non-linear galaxy bias. Using a grid of cosmological N-body simulations, we construct a Taylor-expansion emulator that predicts the galaxy autocorrelation $\xi_{\text{gg}}(r)$ and galaxy-matter cross-correlation $\xi_{\text{gm}}(r)$ as a function of $\sigma_8$, $\Omega_m$, and halo occupation distribution (HOD) parameters, which are allowed to vary with large scale environment to represent possible effects of galaxy assembly bias. We present forecasts for a fiducial case that corresponds to BOSS LOWZ galaxy clustering and SDSS-depth weak lensing (effective source density $\sim 0.3$ arcmin$^{-2}$). Using tangential shear and projected correlation function measurements over $0.5 \leq r_p \leq 30 \, h^{-1}$ Mpc yields a 1.8% constraint on the parameter combination $\sigma_8\Omega_m^{0.58}$, a factor of two better than a constraint that excludes non-linear scales ($r_p > 2 \, h^{-1}$ Mpc, $4 \, h^{-1}$ Mpc for $\gamma_t,w_p$). Much of this improvement comes from the non-linear clustering information, which breaks degeneracies among HOD parameters that would otherwise degrade the inference of matter clustering from GGL. Increasing the effective source density to $3$ arcmin$^{-2}$ sharpens the constraint on $\sigma_8\Omega_m^{0.58}$ by a further factor of two. With robust modeling into the non-linear regime, low-redshift measurements of matter clustering at the 1-percent level with clustering+GGL alone are well within reach of current data sets such as those provided by the Dark Energy Survey.

[26]  arXiv:1709.07103 [pdf, other]
Title: Automated Adaptive Optics
Comments: Preprint of an article submitted for consideration in The WSPC Handbook of Astronomical Instrumentation this http URL
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Large area surveys will dominate the forthcoming decades of astronomy and their success requires characterizing thousands of discoveries through additional observations at higher spatial or spectral resolution, and at complementary cadences or periods. Only the full automation of adaptive optics systems will enable high-acuity, high-sensitivity follow-up observations of several tens of thousands of these objects per year, maximizing on-sky time. Automation will also enable rapid response to target-of-opportunity events within minutes, minimizing the time between discovery and characterization.
In June 2012, we demonstrated the first fully automated operation of an astronomical adaptive optics system by observing 125 objects in succession with the Robo-AO system. Efficiency has increased ever since, with a typical night comprising 200-250 automated observations at the visible diffraction limit. By observing tens of thousands of targets in the largest-ever adaptive-optics surveys, Robo-AO has demonstrated the ability to address the follow-up needs of current and future large astronomical surveys.

[27]  arXiv:1709.07106 [pdf, ps, other]
Title: Magnetic Fields of Neutron Stars
Authors: Sushan Konar
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan
Journal-ref: J. Astrophys. Astr. 38(3) 47 (2017)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

This article briefly reviews our current understanding of the evolution of magnetic fields in neutron stars, which basically defines the evolutionary pathways between different observational classes of neutron stars. The emphasis here is on the evolution in binary systems and the newly emergent classes of millisecond pulsars.

[28]  arXiv:1709.07113 [pdf, ps, other]
Title: A Detached Protostellar Disk around a $\sim$0.2 $M_{\odot}$ protostar in a Possible Site of a Multiple Star Formation in a Dynamical Environment in Taurus
Comments: 9 pages, 4 figures, accepted for publication in The Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report ALMA observations in 0.87 mm continuum and $^{12}$CO ($J$ = 3--2) toward a very low-luminosity ($<$0.1 $L_{\odot}$) protostar, which is deeply embedded in one of the densest core, MC27/L1521F, in Taurus with an indication of multiple star formation in a highly dynamical environment. The beam size corresponds to $\sim$20 AU, and we have clearly detected blueshifted/redshifted gas in $^{12}$CO associated with the protostar. The spatial/velocity distributions of the gas show there is a rotating disk with a size scale of $\sim$10 AU, a disk mass of $\sim$10$^{-4}$ $M_{\odot}$ and a central stellar mass of $\sim$0.2 $M_{\odot}$. The observed disk seems to be detachedfrom the surrounding dense gas although it is still embedded at the center of the core whose density is $\sim$10$^{6}$ cm$^{-3}$. The current low outflow activity and the very-low luminosity indicate that the mass accretion rate onto the protostar is extremely low in spite of a very early stage of star formation. We may be witnessing the final stage of the formation of $\sim$0.2 $M_{\odot}$ protostar. However, we cannot explain the observed low-luminosity with the standard pre-main-sequence evolutionary track, unless we assume cold accretion with an extremely small initial radius of the protostar ($\sim$0.65 $R_\odot$). These facts may challenge our current understanding of the low-mass star formation, in particular, the mass accretion process onto the protostar and the circumstellar disk.

[29]  arXiv:1709.07152 [pdf, other]
Title: Observing Compact Stars with AstroSat
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan."
Journal-ref: Journal of Astrophysics and Astronomy, Vol. 38, Article 51, Sep 2017
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE)

This article presents a brief description of India's AstroSat mission which is a powerful space based observatory for compact star research. An account is given of observational constraints and spectral and timing capabilities as realised post-launch. Some preliminary results of observations of the Crab pulsar and an X-ray binary system GX~301-2 are presented to illustrate some of the capabilities of the mission.

[30]  arXiv:1709.07167 [pdf, other]
Title: The Science Case for Simultaneous mm-Wavelength Receivers in Radio Astronomy
Comments: accepted New Astronomical Reviews
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

This review arose from the European Radio Astronomy Technical Forum (ERATec) meeting held in Firenze, October 2015, and aims to highlight the breadth and depth of the high-impact science that will be aided and assisted by the use of simultaneous mm-wavelength receivers. Recent results and opportunities are presented and discussed from the fields of: continuum VLBI (observations of weak sources, astrometry, observations of AGN cores in spectral index and Faraday rotation), spectral line VLBI (observations of evolved stars and massive star-forming regions) and time domain observations of the flux variations arising in the compact jets of X-ray binaries. Our survey brings together a large range of important science applications, which will greatly benefit from simultaneous observing at mm-wavelengths. Such facilities are essential to allow these applications to become more efficient, more sensitive and more scientifically robust. In some cases without simultaneous receivers the science goals are simply unachievable. Similar benefits would exist in many other high frequency astronomical fields of research.

[31]  arXiv:1709.07179 [pdf, ps, other]
Title: The Nature of Coherent Radio Emission from Pulsars
Authors: Dipanjan Mitra
Comments: 15 pages, 6 figures: "Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan."
Journal-ref: 2017, JApA (Journal of Astronomy and Astrophysics, 38, 52
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The pulsar radio emission originates from regions below 10% of the light cylinder radius. This requires a mechanism where coherent emission is excited in relativistic pair plasma with frequency $\nu_{cr}$ which is below the plasma frequency $\nu_{\circ}$ i.e. $\nu_{cr} < \nu_{\circ}$. A possible model for the emission mechanism is charged bunches (charged solitons) moving relativistically along the curved open dipolar magnetic field lines capable of exciting coherent curvature radio emission. In this article we review the results from high quality observations in conjunction with theoretical models to unravel the nature of coherent curvature radio emission in pulsars.

[32]  arXiv:1709.07191 [pdf, other]
Title: Design and construction of the POLAR detector
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The POLAR detector is a space based Gamma Ray Burst (GRB) polarimeter with a wide field of view, which covers almost half the sky. The instrument uses Compton scattering of gamma rays on a plastic scintillator hodoscope to measure the polarization of the incoming photons. The instrument has been successfully launched on board of the Chinese space laboratory Tiangong~2 on September 15, 2016. The construction of the instrument components is described in this article. Details are provided on problems encountered during the construction phase and their solutions. Initial performance of the instrument in orbit is as expected from ground tests and Monte Carlo simulation.

[33]  arXiv:1709.07202 [pdf, other]
Title: The radio structure of the peculiar narrow-line Seyfert 1 galaxy candidate J1100+4421
Comments: 8 pages, 5 figures. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Narrow-line Seyfert 1 galaxies (NLS1) are an intriguing subclass of active galactic nuclei. Their observed properties indicate low central black hole mass and high accretion rate. The extremely radio-loud NLS1 sources often show relativistic beaming and are usually regarded as younger counterparts of blazars. Recently, the object SDSS J110006.07+442144.3 was reported as a candidate NLS1 source. The characteristics of its dramatic optical flare indicated its jet-related origin. The spectral energy distribution of the object was similar to that of the gamma-ray detected radio-loud NLS1, PMN J0948+0022. Our high-resolution European Very Long Baseline Interferometry Network observations at 1.7 and 5 GHz revealed a compact core feature with a brightness temperature of >~ 10^(10) K. Using the lowest brightness temperature value and assuming a moderate Lorentz factor of ~9 the jet viewing angle is <~ 26 deg. Archival Very Large Array data show a large-scale radio structure with a projected linear size of ~150 kpc reminiscent of double-sided morphology.

[34]  arXiv:1709.07203 [pdf, ps, other]
Title: Measuring black hole mass of type I active galactic nuclei by spectropolarimetry
Authors: Yu-Yang Songsheng, Jian-Min Wang (IHEP)
Comments: MNRAS Letters (accepted): 5 pages, 3 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Black hole (BH) mass of Type I active galactic nuclei (AGN) can be measured or estimated through either reverberation mapping (RM) or empirical $R-L$ relation, however, both of them suffer from uncertainties of the virial factor ($f_{\rm BLR}$), thus limiting the measurement accuracy. In this letter, we make an effort to investigate $f_{\rm BLR}$ through polarised spectra of the broad-line regions (BLR) arisen from electrons in the equatorial plane. Given the BLR composed of discrete clouds with Keplerian velocity around the central BH, we simulate a large number of spectra of total and polarised flux with wide ranges of parameters of the BLR model and equatorial scatters. We find that the $f_{\rm BLR}$-distribution of polarised spectra is much narrower than that of total ones. This provides a way of n accurately estimating BH mass from single spectropolarimetric observations of type I AGN whose equatorial scatters are identified.

[35]  arXiv:1709.07204 [pdf, other]
Title: Cyclotron lines: from magnetic field strength estimators to geometry tracers in neutron stars
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and related objects', celebrating the 75th birth-year of G. Srinivasan
Journal-ref: 2017, JApA, 38, 50M
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

With exactly forty years since the discovery of the first cyclotron line in Her X-1, there have been remarkable advancements in the field related to study of the physics of accreting neutron stars -- cyclotron lines have been a major torchbearer in this regard, from being the only direct estimator of the magnetic field strength, a tracer of accretion geometry and an indicator of the emission beam in these systems. The main flurry of activities have centred around studying the harmonic separations, luminosity dependence, pulse phase dependence and more recently the shapes of the line and the trend for long term evolution in the line energy. This article visits the important results related to cyclotron lines since its discovery and reviews their significance. An emphasis is laid on pulse phase resolved spectroscopy and the important clues a joint timing and spectral study in this context can provide, to build a complete picture for the physics of accretion and hence X-ray emission in accreting neutron stars.

[36]  arXiv:1709.07215 [pdf, other]
Title: Whispers from the edge of physics
Authors: N. Andersson
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and related objects', celebrating the 75th birth-year of G. Srinivasan
Journal-ref: J. Astrophys. Astr. (2017) 38:58
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Neutron stars involve extreme physics which is difficult (perhaps impossible) to explore in laboratory experiments. We have to turn to astrophysical observations, and try to extract information from the entire range of the electromagnetic spectrum. In addition, neutron stars may radiate gravitational waves through a range of scenarios. In this brief summary I outline some of the main ideas, focussing on what we do and do not know, and describe the challenges involved in trying to catch these faint whispers from the very edge of physics.

[37]  arXiv:1709.07230 [pdf, other]
Title: A census of radio-selected AGN on the COSMOS field and of their FIR properties
Comments: 15 pages, 17 figures, to appear in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We use the new catalogue by Laigle et al. (2016) to provide a full census of VLA-COSMOS radio sources. We identify 90% of such sources and sub-divide them into AGN and star-forming galaxies on the basis of their radio luminosity. The AGN sample is COMPLETE with respect to radio selection at all z<3.5. Out of 704 AGN, 272 have a counterpart in the Herschel maps. By exploiting the better statistics of the new sample, we confirm the results of Magliocchetti et al. (2014): the probability for a radio-selected AGN to be detected at FIR wavelengths is both a function of radio luminosity and redshift, whereby powerful sources are more likely FIR emitters at earlier epochs. Such an emission is due to star-forming processes within the host galaxy. FIR emitters and non-FIR emitters only differentiate in the z<1 universe. At higher redshifts they are indistinguishable from each other, as there is no difference between FIR-emitting AGN and star-forming galaxies. Lastly, we focus on radio AGN which show AGN emission at other wavelengths. We find that MIR emission is mainly associated with ongoing star-formation and with sources which are smaller, younger and more radio luminous than the average parent population. X-ray emitters instead preferentially appear in more massive and older galaxies. We can therefore envisage an evolutionary track whereby the first phase of a radio-active AGN and of its host galaxy is associated with MIR emission, while at later stages the source becomes only active at radio wavelengths and possibly also in the X-ray.

[38]  arXiv:1709.07231 [pdf, ps, other]
Title: NuSTAR spectral analysis of two bright Seyfert 1 galaxies: MCG +8-11-11 and NGC 6814
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We report on the NuSTAR observations of two bright Seyfert 1 galaxies, namely MCG +8-11-11 (100 ks) and NGC 6814 (150 ks). The main goal of these observations was to investigate the Comptonization mechanisms acting in the innermost regions of AGN which are believed to be responsible for the UV/X-ray emission. The spectroscopic analysis of the NuSTAR spectra of these two sources revealed that although they had different properties overall (black hole masses, luminosity and Eddington ratios) they had very similar coronal properties. Both presented a power law spectrum with a high-energy cutoff at $\sim 150-200$ keV, a relativistically broadened Fe K$\alpha$ line and the associated disk reflection component, plus a narrow iron line likely emitted in Compton thin and distant matter. The intrinsic continuum was well described by Comptonization models that show for MCG +8-11-11 a temperature of the coronal plasma of kT$_{\rm e} \sim$ 60 keV and an extrapolated optical depth $\tau$=0.84; for NGC 6814 the coronal temperature was kT$_{\rm e} \sim$ 45 keV with an extrapolated optical depth of $\tau$=0.55. We compare and discuss these values to some most common Comptonization models which aim at explaining the energy production and stability of coronae in active galactic nuclei.

[39]  arXiv:1709.07233 [pdf, other]
Title: The radio and X-ray mode-switching pulsar PSR B0943+10
Comments: Published in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan
Journal-ref: J. Astrophys. Astr. (September 2017) 38:54
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Observations obtained in the last years challenged the widespread notion that rotation-powered neutron stars are steady X-ray emitters. Besides a few allegedly rotation-powered neutron stars that showed "magnetar-like" variability, a particularly interesting case is that of PSR B0943+10. Recent observations have shown that this pulsar, well studied in the radio band where it alternates between a bright and a quiescent mode, displays significant X-ray variations, anticorrelated in flux with the radio emission. The study of such synchronous radio/X-ray mode switching opens a new window to investigate the processes responsible for the pulsar radio and high-energy emission. Here we review the main X-ray properties of PSR B0943+10 derived from recent coordinated X-ray and radio observations.

[40]  arXiv:1709.07258 [pdf, other]
Title: Model-independent Constraints on Cosmic Curvature and Opacity
Comments: 7 pages, 3 figures and 2 tables
Journal-ref: Astrophys.J. 847 (2017) no.1, 45
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

In this paper, we propose to estimate the spatial curvature of the universe and the cosmic opacity in a model-independent way with expansion rate measurements, $H(z)$, and type Ia supernova (SNe Ia). On the one hand, using a nonparametric smoothing method Gaussian process, we reconstruct a function $H(z)$ from opacity-free expansion rate measurements. Then, we integrate the $H(z)$ to obtain distance modulus $\mu_{\rm H}$, which is dependent on the cosmic curvature. On the other hand, distances of SNe Ia can be determined by their photometric observations and thus are opacity-dependent. In our analysis, by confronting distance moduli $\mu_{\rm H}$ with those obtained from SNe Ia, we achieve estimations for both the spatial curvature and the cosmic opacity without any assumptions for the cosmological model. Here, it should be noted that light curve fitting parameters, accounting for the distance estimation of SNe Ia, are determined in a global fit together with the cosmic opacity and spatial curvature to get rid of the dependence of these parameters on cosmology. In addition, we also investigate whether the inclusion of different priors for the present expansion rate ($H_0$: global estimation, $67.74\pm 0.46~\rm km~ s^{-1} ~Mpc^{-1}$, and local measurement, $73.24\pm 1.74~\rm km~ s^{-1} ~Mpc^{-1}$) exert influence on the reconstructed $H(z)$ and the following estimations of the spatial curvature and cosmic opacity. Results show that, in general, a spatially flat and transparent universe is preferred by the observations. Moreover, it is suggested that priors for $H_0$ matter a lot. Finally, we find that there is a strong degeneracy between the curvature and the opacity.

[41]  arXiv:1709.07260 [pdf, ps, other]
Title: Neutron Stars: Laboratories for fundamental physics under extreme astrophysical conditions
Comments: 16 pages, 6 figures; Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan."
Journal-ref: J. Astrophys. Astr. 38 (2017) 37
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We discuss different exotic phases and components of matter from the crust to the core of neutron stars based on theoretical models for equations of state relevant to core collapse supernova simulations and neutron star merger. Parameters of the models are constrained from laboratory experiments. It is observed that equations of state involving strangeness degrees of freedom such as hyperons and Bose-Einstein condensates are compatible with 2M$_{solar}$ neutron stars. The role of hyperons is explored on the evolution and stability of the protoneutron star (PNS) in the context of SN1987A. Moment of inertia, mass and radius which are direct probes of neutron star interior are computed and their observational consequences are discussed. We continue our study on the dense matter under strong magnetic fields and its application to magnetoelastic oscillations of neutron stars.

[42]  arXiv:1709.07265 [pdf, other]
Title: Young and Intermediate-age Distance Indicators
Authors: Smitha Subramanian (KIAA/PKU), Massimo Marengo (Iowa State University), Anupam Bhardwaj (University of Delhi), Yang Huang (KIAA/PKU), Laura Inno (MPIA), Akiharu Nakagawa (Kagoshima University), Jesper Storm (AIP)
Comments: Review article, 63 pages (28 figures), Accepted for publication in Space Science Reviews (Chapter 3 of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Age)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Distance measurements beyond geometrical and semi-geometrical methods, rely mainly on standard candles. As the name suggests, these objects have known luminosities by virtue of their intrinsic proprieties and play a major role in our understanding of modern cosmology. The main caveats associated with standard candles are their absolute calibration, contamination of the sample from other sources and systematic uncertainties. The absolute calibration mainly depends on their chemical composition and age. To understand the impact of these effects on the distance scale, it is essential to develop methods based on different sample of standard candles. Here we review the fundamental properties of young and intermediate-age distance indicators such as Cepheids, Mira variables and Red Clump stars and the recent developments in their application as distance indicators.

[43]  arXiv:1709.07284 [pdf, other]
Title: On the extended stellar structure around NGC 288
Comments: 7 pages, 3 figures. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report on observational evidence of an extra-tidal clumpy structure around NGC 288 from an homogeneous coverage of a large area with the Pan-STARRS PS1 database. The extra-tidal star population has been disentangled from that of the Milky Way field by using a cleaning technique that successfully reproduced the stellar density, luminosity function and colour distributions of MW field stars. We have produced the cluster stellar density radial profile and a stellar density map from independent approaches, from which we found results in excellent agreement : the feature extends up to 3.5 times the cluster tidal radius. Previous works based on shallower photometric data sets have speculated on the existence of several long tidal tails, similar to that found in Pal 5. The present outcome shows that NGC 288 could hardly have such tails, but favours the notion that interactions with the MW tidal field has been a relatively inefficient process for stripping stars off the cluster. These results point to the need of a renewed overall study of the external regions of Galactic globular clusters (GGCs) in order to reliably characterise them. Hence, it will be possible to investigate whether there is any connection between detected tidal tails, extra-tidal stellar populations, extent diffuse halo-like structures with the GGCs' dynamical histories in the Galaxy.

[44]  arXiv:1709.07288 [pdf, ps, other]
Title: Superfluidity and Superconductivity in Neutron Stars
Authors: N. Chamel
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on "Physics of Neutron Stars and Related Objects", celebrating the 75th birth-year of G. Srinivasan
Journal-ref: J. Astrophys. Astr. 38, 43 (2017)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Neutron stars, the compact stellar remnants of core-collapse supernova explosions, are unique cosmic laboratories for exploring novel phases of matter under extreme conditions. In particular, the occurrence of superfluidity and superconductivity in neutron stars will be briefly reviewed.

[45]  arXiv:1709.07292 [pdf, other]
Title: Radiation from rapidly rotating oblate neutron stars
Comments: 19 pages, 12 figures. Submitted to A&A. Comments very welcome!
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

A theoretical framework for emission originating from rapidly rotating oblate compact objects is described in detail. By using a Hamilton-Jacobi formalism, we show how the special relativistic rotational effects such as aberration of angles, Doppler boosting, and time dilatation naturally emerge from the general relativistic treatment of rotating compact objects. We use the Butterworth-Ipser metric expanded up to the second order in rotation and hence include effects of light bending, frame-dragging, and quadrupole deviations to our geodesic calculations. We also give detailed descriptions of the numerical algorithms used and provide an open source implementation of the numerical framework called Bender. As an application, we study spectral line profiles (i.e., smearing kernels) from rapidly rotating oblate neutron stars. We find that in this metric description the second order quadrupole effects are not strong enough to produce narrow observable features in the spectral energy distribution for almost any physically realistic parameter combination, and hence, actually detecting them is unlikely. The Full Width at Tenth Maximum and Full Width at Half Maximum of the smearing kernels are also reported for all of the possible viewing angles. These can be then used to quantitatively estimate the effects of rotational smearing on the observed spectra. We also calculate accurate pulse profiles and observer skymaps of emission from hot spots on rapidly rotating accreting millisecond pulsars. These allow us to quantify the strength of the pulse fractions one expects to observe from typical fast spinning millisecond pulsars.

[46]  arXiv:1709.07316 [pdf, other]
Title: HI Intensity Mapping with MeerKAT
Comments: 6 pages, 2 figures; Submitted to the Proceedings of Science, "MeerKAT Science: On the Pathway to the SKA", Stellenbosch, 25-27 May 2016
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We explore the possibility of performing an HI intensity mapping survey with the South African MeerKAT radio telescope, which is a precursor to the Square Kilometre Array (SKA). We propose to use cross-correlations between the MeerKAT intensity mapping survey and optical galaxy surveys, in order to mitigate systematic effects and produce robust cosmological measurements. Our forecasts show that precise measurements of the HI signal can be made in the near future. These can be used to constrain HI and cosmological parameters across a wide range of redshift.

[47]  arXiv:1709.07320 [pdf]
Title: Nanoflare Heating: Observations and Theory
Comments: This is a section for a mega-paper entitled "Achievements of Hinode in the First Ten Years." The invited speakers of the Hinode 10 Conference in Nagoya were asked to each write a section. The contribution should be cited as Klimchuk, J. A. and Hinode Review Team, "Achievements of Hinode in the First Ten Years," 2017, PASJ, submitted
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

This is a review of the observational and theoretical evidence for nanoflare heating of the magnetically-closed corona.

[48]  arXiv:1709.07321 [pdf, other]
Title: Observation of a Large-scale Anisotropy in the Arrival Directions of Cosmic Rays above $8 \times 10^{18}$ eV
Comments: 19 pages (with supplementary material), 8 figures
Journal-ref: Science 357 (22 September 2017) 1266
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Cosmic rays are atomic nuclei arriving from outer space that reach the highest energies observed in nature. Clues to their origin come from studying the distribution of their arrival directions. Using $3 \times 10^4$ cosmic rays above $8 \times 10^{18}$ electron volts, recorded with the Pierre Auger Observatory from a total exposure of 76,800 square kilometers steradian year, we report an anisotropy in the arrival directions. The anisotropy, detected at more than the 5.2$\sigma$ level of significance, can be described by a dipole with an amplitude of $6.5_{-0.9}^{+1.3}$% towards right ascension $\alpha_{d} = 100 \pm 10$ degrees and declination $\delta_{d} = -24_{-13}^{+12}$ degrees. That direction indicates an extragalactic origin for these ultra-high energy particles.

[49]  arXiv:1709.07327 [pdf, other]
Title: The circumstellar envelope around the S-type AGB star W Aql Effects of an eccentric binary orbit
Comments: 10 pages, 8 figures
Journal-ref: A&A 605, A126 (2017)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The CO(J=3-2) emission from the CSE of the binary S-type AGB star W Aql has been observed at subarcsecond resolution using ALMA. The aim of this paper is to investigate the wind properties of the AGB star and to analyse how the known companion has shaped the CSE. The average mass-loss rate during the creation of the detected CSE is estimated through modelling, using the ALMA brightness distribution and previously published single-dish measurements as observational constraints. The ALMA observations are presented and compared to the results from a 3D smoothed particle hydrodynamics (SPH) binary interaction model with the same properties as the W Aql system and with two different orbital eccentricities. Three-dimensional radiative transfer modelling is performed and the response of the interferometer is modelled and discussed. The estimated average mass-loss rate of W~Aql agrees with previous results. The size of the emitting region is consistent with photodissociation models. The CO(J=3-2) emission is dominated by a smooth component overlayed with two weak arc patterns with different separations. The larger pattern is predicted by the binary interaction model with separations of 10" and therefore likely due to the known companion. It is consistent with a binary orbit with low eccentricity. The smaller separation pattern is asymmetric and coincides with the dust distribution, but the separation timescale (200 yrs) is not consistent with any known process of the system. The separation of the known companions of the system is large enough to not have a very strong effect on the circumstellar morphology. The density contrast across the envelope of a binary with an even larger separation will not be easily detectable, even with ALMA, unless the orbit is strongly asymmetric or the AGB star has a much larger mass-loss rate.

[50]  arXiv:1709.07332 [pdf, other]
Title: Revisiting field burial by accretion onto neutron stars
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan
Journal-ref: J Astrophys Astron (2017) 38: 48
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The surface magnetic field strength of millisecond pulsars (MSPs) is found to be about 4 orders of magnitude lower than that of garden variety radio pulsars (with a spin of $\sim 0.5-5$ s and $B\sim 10^{12}$G). The exact mechanism of the apparent reduction of field strength in MSPs is still a subject of debate. One of the proposed mechanisms is burial of the surface magnetic field under matter accreted from a companion. In this article we review the recent work on magnetic confinement of accreted matter on neutron stars poles. We present the solutions of the magneto-static equations with a more accurate equation of state of the magnetically confined plasma and discuss its implications for the field burial mechanism.

[51]  arXiv:1709.07334 [pdf, other]
Title: Observations et modélisations spectro-interférométriques longue base des étoiles et de leur environnement proche
Authors: M. Hadjara
Comments: PhD Thesis 2015, Universite Nice-Sophia Antipoles, in French
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

With the construction of the VLTI (Very Large Telescope Interferometer of the European Observatory ESO for the southern hemisphere) it is now possible to make observations with resolutions of the order of milli-arc-seconds, especially in IR with AMBER instrument (Astronomical Multi Beam Recombine). These new capabilities allow us to better constrain the stellar structures such as polar jets, equatorial disks and flattened photospheres of rotating stars. Thus the estimation of stellar fundamental parameters allows to explore in detail the mechanisms of mass loss, pulsation and magnetism governing the variability and the evolution of the stars.
This thesis presents the results of fast rotating stars observations carried out on the AMBER spectro-interferometer VLTI in its high \& medium spectral resolutions modes. The observations were highly degraded by the optical defects of AMBER and their analysis required the development of specific digital reduction tools to reach the necessary precision for the interferometric measurements interpretation. In order to interpret those measures I developed a chromatic semi-analytical model of rapidly rotating star that allowed me to estimate, from the differential phases; the degree of flattening, the equatorial radius, the rotation velocity, the angle of inclination, the position angle of the star rotation axis in the sky, the local distribution of the effective temperature and the surface gravity of the star within the von Zeipel theorem. The results for four massive stars of spectral types B, A and F have allowed me to characterize the mechanisms discussed above and thus open some prospect for more systematic studies of similar objects, with extending later these studies to the relationship photosphere - circumstellar envelope.

[52]  arXiv:1709.07338 [pdf, ps, other]
Title: Long-term Spectral Variability of the Ultra-luminous X-ray source Holmberg IX X--1
Authors: V. Jithesh (SHAO), Ranjeev Misra (IUCAA), Zhongxiang Wang (SHAO)
Comments: Accepted for publication in ApJ, 12 Pages, 3 Tables, 3 Figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We investigate the long-term spectral variability in the ultra-luminous X-ray source Holmberg IX X--1. By analyzing the data from eight {\it Suzaku} and 13 {\it XMM-Newton} observations conducted between 2001 and 2015, we perform a detailed spectral modeling for all spectra with simple models and complex physical models. We find that the spectra can be well explained by a disc plus thermal Comptonization model. Applying this model, we unveil correlations between the X-ray luminosity ($L_{\rm X}$) and the spectral parameters. Among the correlations, a particular one is the statistically significant positive correlation between $L_{\rm X}$ and the photon index ($\Gamma$), while at the high luminosities of $> 2\times10^{40}\,{\rm~erg\ s}^{-1}$, the source becomes marginally hard and that results a change in the slope of the $\Gamma - L_{\rm X}$ correlation. Similar variability behavior is observed in the optical depth of the source around $L_{\rm X} \sim 2\times10^{40}\,{\rm~erg\ s}^{-1}$ as the source becomes more optically thick. We consider the scenario that a corona covers the inner part of the disc, and the correlations can be explained as to be driven by the variability of seed photons from the disc input into the corona. On the basis of the disc-corona model, we discuss the physical processes that are possibly indicated by the variability of the spectral parameters. Our analysis reveals the complex variability behavior of Holmberg IX X--1 and the variability mechanism is likely related to the geometry of the X-ray emitting regions.

[53]  arXiv:1709.07354 [pdf, other]
Title: A New Precision Measurement of the Small-Scale Line-of-Sight Power Spectrum of the Lyα Forest
Comments: 24 pages, 12 figures, submitted to ApJ, machine readable tables will be made available after publication in the journal
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present a new measurement of the Ly{\alpha} forest power spectrum at $1.8 < z < 3.4$ using 74 Keck/HIRES and VLT/UVES high-resolution, high-S/N quasar spectra. We developed a custom pipeline to measure the power spectrum and its uncertainty, which fully accounts for finite resolution and noise, and corrects for the bias induced by masking missing data, DLAs, and metal absorption lines. Our measurement results in unprecedented precision on the small-scale modes $k > 0.02\,\mathrm{s\,km^{-1}}$, unaccessible to previous SDSS/BOSS analyses. It is well known that these high-$k$ modes are highly sensitive to the thermal state of the intergalactic medium, however contamination by narrow metal lines is a significant concern. We quantify the effect of metals on the small-scale power, and find a modest effect on modes with $k < 0.1\,\mathrm{s\,km^{-1}} $. As a result, by masking metals and restricting to $k < 0.1\,\mathrm{s\,km^{-1}}$ their impact is completely mitigated. We present an end-to-end Bayesian forward modeling framework whereby mock spectra with the same noise, resolution, and masking as our data are generated from Ly{\alpha} forest simulations. These mocks are used to build a custom emulator, enabling us to interpolate between a sparse grid of models and perform MCMC fits. Our results agree well with BOSS on scales $k < 0.02\,\mathrm{s\,km^{-1}}$ where the measurements overlap. The combination of BOSS' percent level low-$k$ precision with our $5-15\%$ high-$k$ measurements, results in a powerful new dataset for precisely constraining the thermal history of the intergalactic medium, cosmological parameters, and the nature of dark matter. The power spectra and their covariance matrices are provided as electronic tables.

[54]  arXiv:1709.07363 [pdf, other]
Title: The impact of vorticity waves on the shock dynamics in core-collapse supernovae
Comments: Submitted to MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Convective perturbations arising from nuclear shell burning can play an important role in propelling neutrino-driven core-collapse supernova explosions. In this work, we analyze the impact of vorticity waves on the shock dynamics and the post-shock flow using the solution of the linear hydrodynamics equations. We show that the entropy perturbations generated by the interaction of the shock with vorticity waves may play a dominant role in generating buoyancy-driven turbulence in the gain region. We estimate that the resulting reduction in the critical luminosity is 17-24%, which approximately agrees with the results of three-dimensional neutrino-hydrodynamics simulations.

[55]  arXiv:1709.07382 [pdf, other]
Title: Clearing residual planetesimals by sweeping secular resonances in transitional disks: a lone-planet scenario for the wide gaps in debris disks around Vega and Fomalhaut
Comments: 20 pages, 12 figures. Accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Extended gaps in the debris disks of both Vega and Fomalhaut have been observed. These structures have been attributed to tidal perturbations by multiple super-Jupiter gas giant planets. Within the current observational limits, however, no such massive planets have been detected. Here we propose a less stringent `lone-planet' scenario to account for the observed structure with a single eccentric gas giant and suggest that clearing of these wide gaps is induced by its sweeping secular resonance. During the depletion of the disk gas, the planet's secular resonance propagates inward and clears a wide gap over an extended region of the disk. Although some residual intermediate-size planetesimals may remain in the gap, their surface density is too low to either produce super-Earths or lead to sufficiently frequent disruptive collisions to generate any observable dusty signatures. The main advantage of this lone-planet sweeping-secular-resonance model over the previous multiple gas giant tidal truncation scenario is the relaxed requirement on the number of gas giants. The observationally inferred upper mass limit can also be satisfied provided the hypothetical planet has a significant eccentricity. A significant fraction of solar or more massive stars bear gas giant planets with significant eccentricities. If these planets acquired their present-day kinematic properties prior to the depletion of their natal disks, their sweeping secular resonance would effectively impede the retention of neighboring planets and planetesimals over a wide range of orbital semi-major axes.

[56]  arXiv:1709.07385 [pdf, other]
Title: Statistical Analysis of Hubble/WFC3 Transit Spectroscopy of Extrasolar Planets
Comments: Accepted for publication in ApJL; 6 pages, 4 figures, 1 table
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Transmission spectroscopy provides a window to study exoplanetary atmospheres, but that window is fogged by clouds and hazes. Clouds and haze introduce a degeneracy between the strength of gaseous absorption features and planetary physical parameters such as abundances. One way to break that degeneracy is via statistical studies. We collect all published HST/WFC3 transit spectra for 1.1-1.65 $\mu$m water vapor absorption, and perform a statistical study on potential correlations between the water absorption feature and planetary parameters. We fit the observed spectra with a template calculated for each planet using the Exo-Transmit code. We express the magnitude of the water absorption in scale heights, thereby removing the known dependence on temperature, surface gravity, and mean molecular weight. We find that the absorption in scale heights has a positive baseline correlation with planetary equilibrium temperature; our hypothesis is that decreasing cloud condensation with increasing temperature is responsible for this baseline slope. However, the observed sample is also intrinsically degenerate in the sense that equilibrium temperature correlates with planetary mass. We compile the distribution of absorption in scale heights, and we find that this distribution is closer to log-normal than Gaussian. However, we also find that the distribution of equilibrium temperatures for the observed planets is similarly log-normal. This indicates that the absorption values are affected by observational bias, whereby observers have not yet targeted a sufficient sample of the hottest planets.

[57]  arXiv:1709.07386 [pdf, other]
Title: Normal and counter Evershed flows in the photospheric penumbra of a sunspot. SPINOR 2D inversions of Hinode-SOT/ SP observations
Comments: Astronomy and Astrophysics, accepted
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Context. The Evershed effect, a nearly horizontal outflow of material seen in the penumbrae of sunspots in the photospheric layers, is a common characteristic of well-developed penumbrae, but is still not well understood. Even less is known about photospheric horizontal inflows in the penumbra, also known as counter Evershed flows. Aims. Here we present a rare feature observed in the penumbra of the main sunspot of AR NOAA 10930. This spot displays the normal Evershed outflow in most of the penumbra, but harbors a fast photospheric inflow of material over a large sector of the disk-center penumbra. We investigate the driving forces of both, the normal and the counter Evershed flows. Methods. We invert the spectropolarimetric data from Hinode SOT/SP using the spatially coupled version of the SPINOR inversion code, which allows us to derive height-dependent maps of the relevant physical parameters in the sunspot. These maps show considerable fine structure. Similarities and differences between the normal Evershed outflow and the counter Evershed flow are investigated. Results. In both the normal and the counter Evershed flows, the material flows from regions with field strengths of the order of 1.5-2 kG to regions with stronger fields. The sources and sinks of both penumbral flows display opposite field polarities, with the sinks (tails of filaments) harboring local enhancements in temperature, which are nonetheless colder than their sources (heads of filaments). Conclusions. The anti-correlation of the gradients in the temperature and magnetic pressure between the endpoints of the filaments from the two distinct penumbral regions is compatible with both the convective driver and the siphon flow scenarios. A geometrical scale of the parameters is necessary to determine which is the dominant force driving the flows.

[58]  arXiv:1709.07388 [pdf, other]
Title: Spectral differences between the jets in `radio loud' and `radio quiet' hard state black hole binaries
Authors: M. Espinasse (École Normale Supérieure de Cachan and Oxford Astrophysics), R. Fender (Oxford)
Comments: Accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We have compiled from the available literature a large set of radio measurements of black hole binaries in the hard X-ray state for which measurements of the gigahertz frequency radio spectral index are possible. We separate the sample into `radio loud' and `radio quiet' subsets based upon their distribution in the radio -- X-ray plane, and investigate the distribution of radio spectral indices within each subset. The distribution of spectral indices of the `radio loud' subset is well described by a Gaussian distribution with mean spectral index $\alpha = +0.2$ and standard deviation $0.2$ (here spectral index is defined such that a positive spectral index means more flux at higher frequencies). The sparser sample for the `radio quiet' subset can be approximated, less well, by a Gaussian with mean $\alpha = -0.2$ and standard deviation $0.3$; alternatively the simple mean of the distribution of the radio quiet subset is $-0.3$. The two spectral index distributions are different at high statistical significance. Confirming previous work in the literature, we test to see if the differences in observed spectra could result from different distributions of jet viewing angles, but find no evidence for this. We conclude therefore that the jets in the two groups are physically different in some way, and briefly discuss possible origins and further possible diagnostics. Finally we note that extrapolating to lower frequencies the two subsets move closer together in the radio -- X-ray plane, and approximately merge into a single distribution at around 400 MHz.

[59]  arXiv:1709.07393 [pdf, ps, other]
Title: On the Intermediate Line Region in AGNs
Comments: 8 pages, 2 figures, Accepted for publication in the Journal Frontiers in Astronomy and Space Sciences
Subjects: Astrophysics of Galaxies (astro-ph.GA)

In this paper we explore the intermediate line region (ILR) by using the photoionisation simulations of the gas clouds present at different radial distances from the center, corresponding to the locations from BLR out to NLR in four types of AGNs. We let for the presence of dust whenever conditions allow for dust existence. All spectral shapes are taken from the recent multi-wavelength campaigns. The cloud density decreases with distance as a power law. We found that the slope of the power law density profile does not affect the line emissivity radial profiles of major emission lines: H${\beta}$, He~II, Mg~II, C~III] ~and [O~III]. When the density of the cloud at the sublimation radius is as high as 10$^{11.5}$ cm$^{-3}$, the ILR should clearly be seen in the observations independently of the shape of the illuminating radiation. Moreover, our result is valid for low ionization nuclear emission regions of active galaxies.

[60]  arXiv:1709.07410 [pdf, other]
Title: Dark Matter Annihilation into Four-Body Final States and Implications for the AMS Antiproton Excess
Comments: 12 pages, 6 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

We consider dark matter annihilation into a general set of final states of Standard Model particles, including two-body and four-body final states that result from the decay of intermediate states. For dark matter masses ~10-10^5 GeV, we use updated data from Planck and from high gamma-ray experiments such as Fermi-LAT, MAGIC, and VERITAS to constrain the annihilation cross section for each final state. The Planck constraints are the most stringent over the entire mass range for annihilation into light leptons, and the Fermi-LAT constraints are the most stringent for four-body final states up to masses ~10^4 GeV. We consider these constraints in light of the recent AMS antiproton results, and show that for light mediators it is possible to explain the AMS data with dark matter, and remain consistent with Fermi-LAT Inner Galaxy measurements, for m_\chi ~ 60-100 GeV mass dark matter and mediator masses m_\phi / m_\chi ~< 1.

[61]  arXiv:1709.07418 [pdf, other]
Title: Radio Afterglows of Gamma Ray Bursts
Authors: Lekshmi Resmi (Indian Institute of Space Science and Technology, India)
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan
Journal-ref: Journal of Astronomy & Astrophysics, 2017
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

This review focuses on the physics of Gamma Ray Bursts probed through their radio afterglow emission. Even though radio band is the least explored of the afterglow spectrum, it has played an important role in the progress of GRB physics, specifically in confirming the hypothesized relativistic effects. Currently radio astronomy is in the beginning of a revolution. The high sensitive Square Kilometer Array (SKA) is being planned, its precursors and pathfinders are about to be operational, and several existing instruments are undergoing upgradation. Thus, the afterglow detection statistics and results from follow up programs are expected to improve in the coming years. We list a few avenues unique to radio band which if explored to full potential have the promise to greatly contribute to the future of GRB physics.

[62]  arXiv:1709.07421 [pdf, other]
Title: Giant Metrewave Radio Telescope Observations of Head-Tail Radio Galaxies
Comments: Accepted for publication in Astronomical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present results from a study of seven large known head-tail radio galaxies based on observations using the Giant Metrewave Radio Telescope at 240 and 610 MHz. These observations are used to study the radio morphologies and distribution of the spectral indices across the sources. The overall morphology of the radio tails of these sources is suggestive of random motions of the optical host around the cluster potential. The presence of the multiple bends an d wiggles in several head-tail sources is possibly due to the precessing radio jets. We find steepening of the spectral index along the radio tails. The prevailing equipartition magnetic field also decreases a long the radio tails of these sources. These steepening trends are attributed to the synchrotron aging of plasma toward the ends of the tails. The dynamical ages of these sample sources have been estimated to be ~100 Myr, which is a factor of six more than the age estimates from the radiative losses due to synchrotron cooling.

[63]  arXiv:1709.07428 [pdf, ps, other]
Title: Neutron Stars in X-ray Binaries and their Environments
Authors: Biswajit Paul
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan
Journal-ref: Journal of Astrophysics and Astronomy, 2017, Vol 38, Issue 3, 39
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Neutron stars in X-ray binary systems are fascinating objects that display a wide range of timing and spectral phenomena in the X-rays. Not only parameters of the neutron stars, like magnetic field strength and spin period evolve in their active binary phase, the neutron stars also affect the binary systems and their immediate surroundings in many ways. Here we discuss some aspects of the interactions of the neutron stars with their environments that are revelaed from their X-ray emission. We discuss some recent developments involving the process of accretion onto high magnetic field neutron stars: accretion stream structure and formation, shape of pulse profile and its changes with accretion torque. Various recent studies of reprocessing of X-rays in the accretion disk surface, vertical structures of the accretion disk and wind of companion star are also discussed here. The X-ray pulsars among the binary neutron stars provide excellent handle to make accurate measurement of the orbital parameters and thus also evolution of the binray orbits that take place over time scale of a fraction of a million years to tens of millions of years. The orbital period evolution of X-ray binaries have shown them to be rather complex systems. Orbital evolution of X-ray binaries can also be carried out from timing of the X-ray eclipses and there have been some surprising results in that direction, including orbital period glitches in two X-ray binaries and possible detection of the most massive circum-binary planet around a Low Mass X-ray Binary.

[64]  arXiv:1709.07430 [pdf, other]
Title: Implications of GW related searches for IceCube
Comments: 4 pages, 1 figure, to appear in Proceedings for the 52nd Rencontres de Moriond, EW session, 2017
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

At the beginning of 2016, LIGO reported the first-ever direct detection of gravitational waves. The measured signal was compatible with the merger of two black holes of about 30 solar masses, releasing about 3 solar masses of energy in gravitational waves. We consider the possible neutrino emission from a binary black hole merger relative to the energy released in gravitational waves and investigate the constraints coming from the non-detection of counterpart neutrinos, focusing on IceCube and its energy range. The information from searches for counterpart neutrinos is combined with the diffuse astrophysical neutrino flux in order to put bounds on neutrino emission from binary black hole mergers. Prospects for future LIGO observation runs are shown and compared with model predictions.

[65]  arXiv:1709.07441 [pdf]
Title: A precise measurement of the orbital period parameters of Cygnus X-3
Comments: 8 pages, 7 figures, Accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present X-ray light curves of Cygnus X-3 as measured by the recently launched AstroSat satellite. The light curve folded over the binary period of 4.8 hours shows a remarkable stability over the past 45 years and we find that we can use this information to measure the zero point to better than 100 s. We revisit the historical binary phase measurements and examine the stability of the binary period over 45 years. We present a new binary ephemeris with the period and period derivative determined to an accuracy much better than previously reported. We do not find any evidence for a second derivative in the period variation. The precise binary period measurements, however, indicate a hint of short term episodic variations in periods. Interestingly, these short term period variations coincide with the period of enhanced jet activity exhibited by the source. We discuss the implications of these observations on the nature of the binary system.