- ID:
- ivo://CDS.VizieR/J/A+A/468/49
- Title:
- LMXBs in the bulge of M31
- Short Name:
- J/A+A/468/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the population of X-ray point sources in the bulge of M31 to contrast properties of various subpopulations, such as persistent and transient sources and primordial LMXBs and dynamically formed ones. Based on the data from 26 archival Chandra observations we study the source content and properties of various subpopulations of X-ray sources to a maximum distance of 12' from the centre of M 31.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/649/A104
- Title:
- Long-term X-ray spectral evolution of ULXsE
- Short Name:
- J/A+A/649/A104
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The discovery of pulsations in several ultraluminous X-ray sources (ULXs) has demonstrated that a fraction of them are powered by super-Eddington accretion onto neutron stars (NSs). This has raised questions regarding the NS to black hole (BH) ratio within the ULX population and the physical mechanism that allows ULXs to reach luminosities well in excess of their Eddington luminosity. Is this latter the presence of strong magnetic fields or rather the presence of strong outflows that collimate the emission towards the observer? In order to distinguish between these scenarios, namely, supercritically accreting BHs, weakly magnetised NSs, or strongly magnetised NSs, we study the long-term X-ray spectral evolution of a sample of 17 ULXs with good long-term coverage, 6 of which are known to host NSs. At the same time, this study serves as a baseline to identify potential new NS-ULX candidates. We combine archival data from Chandra, XMM-Newton, and NuSTAR observatories in order to sample a wide range of spectral states for each source. We track the evolution of each source in a hardness-luminosity diagram (HLD) in order to identify spectral changes, and show that these can be used to constrain the accretion flow geometry, and in some cases the nature of the accretor. We find NS-ULXs to be among the hardest sources in our sample with highly variable high-energy emission. On this basis, we identify M81 X-6 as a strong NS-ULX candidate, whose variability is shown to be akin to that of NGC 1313 X-2. For most softer sources with an unknown accretor, we identify the presence of three markedly different spectral states, which we interpret by invoking changes in the mass-accretion rate and obscuration by the supercritical wind/funnel structure. Finally, we report on a lack of variability at high energies (>~10keV) in NGC 1313 X-1 and Holmberg IX X-1, which we argue may offer a means to differentiate BH-ULXs from NS-ULXs. We support a scenario in which the hardest sources in our sample might be powered by strongly magnetised NSs, meaning that the high-energy emission is dominated by the hard direct emission from the accretion column. Instead, softer sources may be explained by weakly magnetised NSs or BHs, in which the presence of outflows naturally explains their softer spectra through Compton down-scattering, their spectral transitions, and the dilution of the pulsed-emission should some of these sources contain NSs.
- ID:
- ivo://CDS.VizieR/J/ApJ/612/437
- Title:
- Low-luminosity hard X-ray binaries candidates
- Short Name:
- J/ApJ/612/437
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a search for hard X-ray binaries (HXRBs) among previously unidentified sources from ROSAT PSPC pointed observations, using the automated X-ray source classifier ClassX.
- ID:
- ivo://CDS.VizieR/J/ApJ/800/17
- Title:
- Mass-transfer sequences in 16 Galactic LMXBs
- Short Name:
- J/ApJ/800/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic field black hole (BH) low-mass X-ray binaries (LMXBs) are believed to form in situ via the evolution of isolated binaries. In the standard formation channel, these systems survived a common envelope phase, after which the remaining helium core of the primary star and the subsequently formed BH are not expected to be highly spinning. However, the measured spins of BHs in LMXBs cover the whole range of spin parameters. We propose here that the BH spin in LMXBs is acquired through accretion onto the BH after its formation. In order to test this hypothesis, we calculated extensive grids of detailed binary mass-transfer sequences. For each sequence, we examined whether, at any point in time, the calculated binary properties are in agreement with their observationally inferred counterparts of 16 Galactic LMXBs. The "successful" sequences give estimates of the mass that the BH has accreted since the onset of Roche-Lobe overflow. We find that in all Galactic LMXBs with measured BH spin, the origin of the spin can be accounted for by the accreted matter, and we make predictions about the maximum BH spin in LMXBs where no measurement is yet available. Furthermore, we derive limits on the maximum spin that any BH can have depending on current properties of the binary it resides in. Finally we discuss the implication that our findings have on the BH birth-mass distribution, which is shifted by ~1.5M_{sun}_ toward lower masses, compared to the currently observed one.
- 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.
- 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/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/AJ/146/135
- Title:
- Physical parameters of 29 M31 globular clusters
- Short Name:
- J/AJ/146/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Andromeda galaxy, M31, has several times the number of globular clusters found in the Milky Way. It contains a correspondingly larger number of low-mass X-ray binaries (LMXBs) associated with globular clusters, and as such can be used to investigate the cluster properties that lead to X-ray binary formation. The best tracer of the spatial structure of M31 globulars is the high-resolution imaging available from the Hubble Space Telescope (HST), and we have used HST data to derive structural parameters for 29 LMXB-hosting M31 globular clusters. These measurements are combined with structural parameters from the literature for a total of 41 (of 50 known) LMXB clusters and a comparison sample of 65 non-LMXB clusters. Structural parameters measured in blue bandpasses are found to be slightly different (smaller core radii and higher concentrations) than those measured in red bandpasses; this difference is enhanced in LMXB clusters and could be related to stellar population differences. Clusters with LMXBs show higher collision rates for their mass compared to clusters without LMXBs, and collision rates estimated at the core radius show larger offsets than rates estimated at the half-light radius. These results are consistent with the dynamical formation scenario for LMXBs. A logistic regression analysis finds that, as expected, the probability of a cluster hosting an LMXB increases with increasing collision rate and proximity to the galaxy center. The same analysis finds that probability of a cluster hosting an LMXB decreases with increasing cluster mass at a fixed collision rate, although we caution that this could be due to sample selection effects. Metallicity is found to be a less important predictor of LMXB probability than collision rate, mass, or distance, even though LMXB clusters have a higher metallicity on average. This may be due to the interaction of location and metallicity: a sample of M31 LMXBs with a greater range in galactocentric distance would likely contain more metal-poor clusters and make it possible to disentangle the two effects.
