- ID:
- ivo://CDS.VizieR/J/ApJS/193/31
- Title:
- M33 Chandra ACIS survey: final catalog
- Short Name:
- J/ApJS/193/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study presents the final source catalog of the Chandra ACIS Survey of M33 (ChASeM33). With a total exposure time of 1.4Ms, ChASeM33 covers ~70% of the D_25_ isophote (R~4.0kpc) of M33 and provides the deepest, most complete, and detailed look at a spiral galaxy in X-rays. The source catalog includes 662 sources, reaches a limiting unabsorbed luminosity of ~2.4x10^34^erg/s in the 0.35-8.0keV energy band, and contains source positions, source net counts, fluxes and significances in several energy bands, and information on source variability. To constrain the nature of the detected X-ray source, hardness ratios were constructed and spectra were fit for 254 sources, follow-up MMT spectra of 116 sources were acquired, and cross-correlations with previous X-ray catalogs and other multi-wavelength data were generated. Based on this effort, 183 of the 662 ChASeM33 sources could be identified. Finally, the luminosity function (LF) for the detected point sources as well as the one for the X-ray binaries (XRBs) in M33 is presented. The resulting distribution is consistent with a dominant population of high-mass XRBs as would be expected for M33.
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- ID:
- ivo://CDS.VizieR/J/ApJ/808/19
- Title:
- Megasecond Chandra XVP obs. of NGC3115. II.
- Short Name:
- J/ApJ/808/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carried out an in-depth study of low-mass X-ray binaries (LMXBs) detected in the nearby lenticular galaxy NGC 3115 using the Megasecond Chandra X-ray Visionary Project observation (total exposure time 1.1Ms). In total we found 136 candidate LMXBs in the field and 49 in globular clusters (GCs) above 2{sigma} detection, with 0.3-8keV luminosity L_X_~10^36^-10^39^erg/s. Other than 13 transient candidates, the sources overall have less long-term variability at higher luminosity, at least at L_X_>~2x10^37^erg/s. In order to identify the nature and spectral state of our sources, we compared their collective spectral properties based on single-component models (a simple power law or a multicolor disk) with the spectral evolution seen in representative Galactic LMXBs. We found that in the L_X_ versus photon index {Gamma}_PL_ and L_X_versus disk temperature kT_MCD_ plots, most of our sources fall on a narrow track in which the spectral shape hardens with increasing luminosity below L_X_~7x10^37^erg/s, but is relatively constant ({Gamma}_PL_~1.5 or kT_MCD_~1.5keV) above this luminosity, which is similar to the spectral evolution of Galactic neutron star (NS) LMXBs in the soft state in the Chandra bandpass. Therefore, we identified the track as the NS LMXB soft-state track and suggested sources with L_X_<~7x10^37^erg/s as atolls in the soft state and those with L_X_>~7x10^37^erg/s as Z sources. Ten other sources (five are transients) displayed significantly softer spectra and are probably black hole X-ray binaries in the thermal state. One of them (persistent) is in a metal-poor GC.
- ID:
- ivo://CDS.VizieR/J/A+A/581/A83
- Title:
- Metal enriched X-ray bursting neutron star atmos.
- Short Name:
- J/A+A/581/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-mass X-ray binaries hosting neutron stars (NS) exhibit thermonuclear (type-I) X-ray bursts, which are powered by unstable nuclear burning of helium and/or hydrogen into heavier elements deep in the NS "ocean". In some cases the burning ashes may rise from the burning depths up to the NS photosphere by convection, leading to the appearance of the metal absorption edges in the spectra, which then force the emergent X-ray burst spectra to shift toward lower energies. These effects may have a substantial impact on the color correction factor fc and the dilution factor w, the parameters of the diluted blackbody model F_E_=wB_E_(f_c_T_eff_) that is commonly used to describe the emergent spectra from NSs. The aim of this paper is to quantify how much the metal enrichment can change these factors. We have developed a new NS atmosphere modeling code, which has a few important improvements compared to our previous code required by inclusion of the metals. The opacities and the internal partition functions (used in the ionization fraction calculations) are now taken into account for all atomic species. In addition, the code is now parallelized to counter the increased computational load.
- ID:
- ivo://CDS.VizieR/J/AcA/41/73
- Title:
- Model atmospheres of X-ray bursting neutron stars
- Short Name:
- J/AcA/41/73
- 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 the first detailed tables which show the structure of plane--parallel hydrogen-helium atmospheres of bursting neutron stars. Hydrogen-helium 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/694/1115
- Title:
- Modulation in the X-ray binary SAX J1808.4-3658
- Short Name:
- J/ApJ/694/1115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on optical imaging of the X-ray binary SAX J1808.4-3658 with the 8m Gemini South Telescope. The binary, containing an accretion-powered millisecond pulsar, appears to have a large periodic modulation in its quiescent optical emission. In order to clarify the origin of this modulation, we obtained three time-resolved r'-band light curves (LCs) of the source over five days. The LCs can be described by a sinusoid, and the long time-span between them allows us to determine optical period P=7251.9s and phase 0.671 at MJD 54599.0 (TDB; phase 0.0 corresponds to the ascending node of the pulsar orbit), with uncertainties of 2.8s and 0.008 (90% confidence), respectively. This periodicity is highly consistent with the X-ray orbital ephemeris.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A2
- Title:
- 100-month Swift catalogue of SFXTs
- Short Name:
- J/A+A/562/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Supergiant Fast X-ray Transients (SFXTs) are High Mass X-ray Binaries (HMXBs) that are defined by their hard X-ray flaring behaviour. During such flares they reach peak luminosities of 10^36^-10^37^erg/s for a few hours (in the hard X-ray): much shorter timescales than those characterizing Be/X-ray binaries. We investigate the characteristics of bright flares (detections in excess of 5{sigma}) for a sample of SFXTs and their relation to the orbital phase. We have retrieved all Swift/BAT Transient Monitor light curves, and collected all detections in excess of 5{sigma} from both daily- and orbital-averaged light curves in the time range 2005 February 12 to 2013 May 31 (MJD 53413-56443). We also considered all on-board detections as recorded in the same time span and selected those within 4 arcmin of each source in our sample and in excess of 5{sigma}. We present a catalogue of over a thousand BAT flares from 11 SFXTs, down to 15-150keV fluxes of ~6x10^-10^erg/cm^2^/s (daily timescale) and ~1.5x10^-9^erg/cm^2^/s (orbital timescale, averaging ~800s) and spanning 100 months. The great majority of these flares are unpublished. This population is characterized by short (a few hundred seconds) and relatively bright (in excess of 100mCrab, 15-50keV) events. In the hard X-ray, these flares last in general much less than a day. Clustering of hard X-ray flares can be used to indirectly measure the length of an outburst, even when the low-level emission is not detected. We construct the distributions of flares, of their significance (in terms of sigma) and their flux as a function of orbital phase, to infer the properties of these binary systems. In particular, we observe a trend of clustering of flares at some phases as P_orb increases, as consistent with a progression from tight, circular or mildly eccentric orbits at short periods, to wider and more eccentric orbits at longer orbital periods. Finally, we estimate the expected number of flares for a given source for our limiting flux and provide the recipe for calculating them for the limiting flux of future hard X-ray observatories.
- ID:
- ivo://CDS.VizieR/J/MNRAS/483/5554
- Title:
- Non-nuclear X-ray sources in nearby galaxies
- Short Name:
- J/MNRAS/483/5554
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have created a new, clean catalogue of extragalactic non-nuclear X-ray sources by correlating the 3XMM-DR4 data release of the XMM-Newton Serendipitous Source Catalogue with the Third Reference Catalogue of Bright Galaxies and the Catalogue of Neighbouring Galaxies, using an improved version of the method presented in Walton et al. (2011MNRAS.416.1844W, Cat. J/MNRAS/416/1844). Our catalogue contains 1314 sources, of which 384 are candidate ultraluminous X-ray sources (ULXs). The resulting catalogue improves upon previous catalogues in its handling of spurious detections by taking into account XMM-Newton quality flags. We estimate the contamination of ULXs by background sources to be 24 per cent. We define a 'complete' subsample as those ULXs in galaxies for which the sensitivity limit is below 10^39^erg/s and use it to examine the hardness ratio properties between ULX and non-ULX sources, and ULXs in different classes of host galaxy. We find that ULXs have a similar hardness ratio distribution to lower-luminosity sources, consistent with previous studies. We also find that ULXs in spiral and elliptical host galaxies have similar distributions to each other independent of host galaxy morphology, however our results do support previous indications that the population of ULXs is more luminous in star-forming host galaxies than in non-star-forming galaxies. Our catalogue contains further interesting subpopulations for future study, including Eddington Threshold sources and highly variable ULXs. We also examine the highest-luminosity (L_X_ >5x10^40^erg/s) ULXs in our catalogue in search of intermediate-mass black hole candidates, and find nine new possible candidates
- ID:
- ivo://CDS.VizieR/J/ApJ/825/132
- Title:
- NuSTAR hard X-ray survey of the Galactic Center. II.
- Short Name:
- J/ApJ/825/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first survey results of hard X-ray point sources in the Galactic Center (GC) region by NuSTAR. We have discovered 70 hard (3-79 keV) X-ray point sources in a 0.6 deg^2^ region around Sgr A* with a total exposure of 1.7 Ms, and 7 sources in the Sgr B2 field with 300 ks. We identify clear Chandra counterparts for 58 NuSTAR sources and assign candidate counterparts for the remaining 19. The NuSTAR survey reaches X-ray luminosities of ~4x and ~8x10^32^ erg/s at the GC (8 kpc) in the 3-10 and 10-40 keV bands, respectively. The source list includes three persistent luminous X-ray binaries (XBs) and the likely run-away pulsar called the Cannonball. New source-detection significance maps reveal a cluster of hard (>10 keV) X-ray sources near the Sgr A diffuse complex with no clear soft X-ray counterparts. The severe extinction observed in the Chandra spectra indicates that all the NuSTAR sources are in the central bulge or are of extragalactic origin. Spectral analysis of relatively bright NuSTAR sources suggests that magnetic cataclysmic variables constitute a large fraction (>40%-60%). Both spectral analysis and logN-logS distributions of the NuSTAR sources indicate that the X-ray spectra of the NuSTAR sources should have kT>20 keV on average for a single temperature thermal plasma model or an average photon index of {Gamma}=1.5-2 for a power-law model. These findings suggest that the GC X-ray source population may contain a larger fraction of XBs with high plasma temperatures than the field population.
- ID:
- ivo://CDS.VizieR/J/PAZh/26/13
- Title:
- Observations of X-ray binary A0535+26/V725 Tau
- Short Name:
- J/PAZh/26/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UBV photoelectric observations of A0535+26/V725 Tau are obtained at Crimean Station of SAI in 1980 and 1988-1998.
- ID:
- ivo://CDS.VizieR/J/ApJ/856/38
- Title:
- Optical LCs of the counterpart to IC 10 X-2
- Short Name:
- J/ApJ/856/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an optical and infrared (IR) study of IC 10 X-2, a high-mass X-ray binary in the galaxy IC 10. Previous optical and X-ray studies suggest that X-2 is a Supergiant Fast X-ray Transient: a large-amplitude (factor of ~100), short-duration (hours to weeks) X-ray outburst on 2010 May 21. We analyze R- and g-band light curves of X-2 from the intermediate Palomar Transient Factory taken between 2013 July 15 and 2017 February 14 that show high-amplitude (>~1mag), short-duration (<~8days) flares and dips (>~0.5mag). Near-IR spectroscopy of X-2 from Palomar/TripleSpec show He I, Paschen-{gamma}, and Paschen-{beta} emission lines with similar shapes and amplitudes as those of luminous blue variables (LBVs) and LBV candidates (LBVc). Mid-IR colors and magnitudes from Spitzer/Infrared Array Camera photometry of X-2 resemble those of known LBV/LBVcs. We suggest that the stellar companion in X-2 is an LBV/LBVc and discuss possible origins of the optical flares. Dips in the optical light curve are indicative of eclipses from optically thick clumps formed in the winds of the stellar counterpart. Given the constraints on the flare duration (0.02-0.8 days) and the time between flares (15.1+/-7.8days), we estimate the clump volume filling factor in the stellar winds, f_V_, to be 0.01<f_V_<0.71, which overlaps with values measured from massive star winds. In X-2, we interpret the origin of the optical flares as the accretion of clumps formed in the winds of an LBV/LBVc onto the compact object.
