- ID:
- ivo://CDS.VizieR/J/A+A/527/A139
- Title:
- X-ray bursting neutron star atmosphere models
- Short Name:
- J/A+A/527/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray bursting neutron stars in low mass X-ray binaries constitute an appropriate source class to constrain masses and radii of neutron stars, but a sufficiently extended set of corresponding model atmospheres is necessary for these investigations. Methods. We computed such a set of model atmospheres and emergent spectra in a plane-parallel, hydrostatic, and LTE approximation with Compton scattering taken into account.
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- ID:
- ivo://CDS.VizieR/J/ApJ/817/95
- Title:
- X-ray observations of HCG galaxies
- Short Name:
- J/ApJ/817/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain total galaxy X-ray luminosities, L_X_, originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the +/-1{sigma} scatter of the Mineo et al. L_X_-star formation rate (SFR) correlation or have higher L_X_ than predicted by this correlation for their SFR. We discuss how these "excesses" may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. L_X_-stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low- or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme L_X_ values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high L_X_ values can be observed due to strong XRB variability.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/136
- Title:
- X-ray obs. of SINGS gal. compared to models
- Short Name:
- J/ApJ/774/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the largest-scale comparison to date between observed extragalactic X-ray binary (XRB) populations and theoretical models of their production. We construct observational X-ray luminosity functions (oXLFs) using Chandra observations of 12 late-type galaxies from the Spitzer Infrared Nearby Galaxy Survey. For each galaxy, we obtain theoretical XLFs (tXLFs) by combining XRB synthetic models, constructed with the population synthesis code StarTrack, with observational star formation histories (SFHs). We identify highest-likelihood models both for individual galaxies and globally, averaged over the full galaxy sample. Individual tXLFs successfully reproduce about half of the oXLFs, but for some galaxies we are unable to find underlying source populations, indicating that galaxy SFHs and metallicities are not well matched and/or that XRB modeling requires calibration on larger observational samples. Given these limitations, we find that the best models are consistent with a product of common envelope ejection efficiency and central donor concentration =~0.1, and a 50% uniform-50% "twins" initial mass-ratio distribution. We present and discuss constituent subpopulations of tXLFs according to donor, accretor, and stellar population characteristics. The galaxy-wide X-ray luminosity due to low-mass and high-mass XRBs, estimated via our best global model tXLF, follows the general trend expected from the L_X_-star formation rate and L_X_-stellar mass relations of Lehmer et al. Our best models are also in agreement with modeling of the evolution of both XRBs over cosmic time and of the galaxy X-ray luminosity with redshift.
- ID:
- ivo://CDS.VizieR/J/A+A/407/1039
- Title:
- X-ray power spectra of Cygnus X-1
- Short Name:
- J/A+A/407/1039
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the long term evolution of the timing properties of the black hole candidate Cygnus X-1 in the 0.002-128 Hz frequency range as monitored from 1998 to 2001 with the Rossi X-ray Timing Explorer (RXTE). For most of this period the source was in its hard state.
- ID:
- ivo://CDS.VizieR/J/ApJ/797/91
- Title:
- X-Ray source properties for NGC 2207/IC 2163
- Short Name:
- J/ApJ/797/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive study of the total X-ray emission from the colliding galaxy pair NGC 2207/IC 2163, based on Chandra, Spitzer, and GALEX data. We detect 28 ultraluminous X-ray sources (ULXs), 7 of which were not detected previously because of X-ray variability. Twelve sources show significant long-term variability, with no correlated spectral changes. Seven sources are transient candidates. One ULX coincides with an extremely blue star cluster (B-V=-0.7). We confirm that the global relation between the number and luminosity of ULXs and the integrated star-formation rate (SFR) of the host galaxy also holds on local scales. We investigate the effects of dust extinction and age on the X-ray binary (XRB) population on subgalactic scales. The distributions of N_X_ and L_X_ are peaked at L_IR_/L_NUV_~1, which may be associated with an age of ~10 Myr for the underlying stellar population. We find that approximately one-third of the XRBs are located in close proximity to young star complexes. The luminosity function of the XRBs is consistent with that typical for high-mass XRBs and appears unaffected by variability. We disentangle and compare the X-ray diffuse spectrum with that of the bright XRBs. The hot interstellar medium dominates the diffuse X-ray emission at E<~1 keV and has a temperature kT=0.28_-0.04_^+0.05^ keV and intrinsic 0.5-2 keV luminosity of 7.9x10^40^ erg/s, a factor of ~2.3 higher than the average thermal luminosity produced per unit SFR in local star-forming galaxies. The total X-ray output of NGC 2207/IC 2163 is 1.5x10^41^ erg/s, and the corresponding total integrated SFR is 23.7 M_{sun}_/yr.
- ID:
- ivo://CDS.VizieR/J/ApJ/599/1067
- Title:
- X-ray sources in M104
- Short Name:
- J/ApJ/599/1067
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the population of point sources discovered during an 18.5ks Chandra ACIS-S observation of the Sombrero galaxy. We present the luminosity function and the spectra of the six brightest sources, consider correlations with globular clusters (GCs) and with planetary nebulae, and study the galaxy's population of very soft sources. We detected 122 sources. Twenty-two sources are identified as very soft; of these, five appear to be classical luminous supersoft X-ray sources (SSSs), while 17 may belong to the slightly harder class referred to as quasi-soft (QSSs). There is an overdensity of very soft sources within 2kpc of the nucleus, which is itself the brightest X-ray source. Very soft sources are also found in the disk and halo, with one QSS in a globular cluster (GC).
- ID:
- ivo://CDS.VizieR/J/MNRAS/422/2302
- Title:
- X-ray sources in the Phoenix dwarf galaxy
- Short Name:
- J/MNRAS/422/2302
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the first X-ray images of the Phoenix dwarf galaxy, taken with XMM-Newton in 2009 July. This Local Group dwarf galaxy shares similarities with the Small Magellanic Cloud (SMC) including a burst of star formation ~50Myr ago. The SMC has an abundance of high-mass X-ray binaries (HMXBs) and so we have investigated the possibility of an HMXB population in Phoenix with the intention of furthering the understanding of the HMXB-star formation rate relation. The data from the combined European Photon Imaging Cameras (EPIC) were used to distinguish between different source classes [foreground stars, background galaxies, active galactic nuclei (AGN) and supernova remnants] using EPIC hardness ratios and correlations with optical and radio catalogues.
- ID:
- ivo://CDS.VizieR/J/ApJ/376/161
- Title:
- X-ray spectra of bursting neutron stars
- Short Name:
- J/ApJ/376/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray burst sources represent a class of accreting neutron stars in close binary systems which do not exhibit any traces of the magnetic field. We present new method of hot model atmosphere computations with account of Compton scattering on free electrons and computed set of plane-parallel hydrogen-helium atmospheres and X-ray spectra of bursting neutron stars. Models were computed with precise angle-dependent radiative transfer under constrains of radiative and hydrostatic equilibrium. Compton scattering opacity included both the Klein-Nishina corrections and the effects of relativistic Maxwellian thermal motion of scattering electrons. Compton redistribution function allows for large energy exchange between X-ray photons and scattering electrons.
- ID:
- ivo://CDS.VizieR/J/ApJ/865/43
- Title:
- X-ray stacking analysis of Chandra-COSMOS gal.
- Short Name:
- J/ApJ/865/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an X-ray stacking analysis of ~75000 star-forming galaxies between 0.1<z<5.0 using the Chandra COSMOS-Legacy survey to study the X-ray emission of low-luminosity active galactic nuclei (AGN) and its connection to host galaxy properties. The stacks at z<0.9 have luminosity limits as low as 10^40^-10^41^erg/s, a regime in which X-ray binaries (XRBs) can dominate the X-ray emission. Comparing the measured luminosities to established XRB scaling relations, we find that the redshift evolution of the luminosity per star formation rate (SFR) of XRBs depends sensitively on the assumed obscuration and may be weaker than previously found. The XRB scaling relation based on stacks from the Chandra Deep Field South overestimates the XRB contribution to the COSMOS high specific SFR stacks, possibly due to a bias affecting the CDF-S stacks because of their small galaxy samples. After subtracting the estimated XRB contribution from the stacks, we find that most stacks at z>1.3 exhibit a significant X-ray excess indicating nuclear emission. The AGN emission is strongly correlated with stellar mass but does not exhibit an additional correlation with SFR. The hardness ratios of the high-redshift stacks indicate that the AGN are substantially obscured (N_H_~10^23^cm^-2^). These obscured AGN are not identified by IRAC color selection and have L_X_~10^41^-10^43^erg/s, consistent with accretion at an Eddington rate of ~10^-3^ onto 10^7^-10^8^M_{sun}_ black holes. Combining our results with other X-ray studies suggests that AGN obscuration depends on stellar mass and an additional variable, possibly the Eddington rate.
- ID:
- ivo://CDS.VizieR/J/ApJS/177/465
- Title:
- X-ray variability in NGC 6946, NGC 4485/90
- Short Name:
- J/ApJS/177/465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze data from five Chandra observations of the spiral galaxy NGC 6946 and from three Chandra observations of the irregular/spiral interacting galaxy pair NGC 4485/4490, with an emphasis on investigating the long-term variability exhibited by the source populations. We detect 90 point sources coincident with NGC 6946 down to luminosities of a few times 10^36^ergs/s, and 38 sources coincident with NGC 4485/90 down to a luminosity of ~1x10^37^ergs/s. Twenty-five (15) sources in NGC 6946 (NGC 4485/90) exhibit long-term (i.e., weeks to years) variability in luminosity; 11 (4) are transient candidates. The single ultraluminous X-ray source (ULX) in NGC 6946 and all but one of the eight ULXs in NGC 4485/90 exhibit long-term flux variability. Two of the ULXs in NGC 4485/90 have not been identified before as ultraluminous sources. The widespread variability in both systems is indicative of the populations being dominated by X-ray binaries, and this is supported by the X-ray colors of the sources. The distribution of colors among the sources indicates a large fraction of high-mass X-ray binaries in both systems. The shapes of the X-ray luminosity functions of the galaxies do not change significantly between observations and can be described by power laws with cumulative slopes ~0.6-0.7 (NGC 6946) and ~0.4 (NGC 4485/90).
