- ID:
- ivo://CDS.VizieR/J/ApJ/689/983
- Title:
- LMXBs in early-type galaxies. I. Chandra
- Short Name:
- J/ApJ/689/983
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a Chandra survey of LMXBs in 24 early-type galaxies. Correcting for detection incompleteness, the X-ray luminosity function (XLF) of each galaxy is consistent with a power law with negative logarithmic differential slope, {beta}~2.0. However, {beta} strongly correlates with incompleteness, indicating the XLF flattens at low-L_X_. Although the XLFs are similar, we find evidence of some variation between galaxies. The high-L_X_ XLF slope does not correlate with age, but may correlate with [{alpha}/Fe]. Considering only LMXBs with L_X_>10^37^ergs/s, matching the LMXBs with globular clusters (GCs) identified in HST observations of 19 of the galaxies, we find the probability a GC hosts an LMXB is proportional to L^{alpha}^_GC_Z^{gamma}^_Fe_ where {alpha}=1.01+/-0.19 and {gamma}=0.33+/-0.11. The spatial distribution of LMXBs resembles that of GCs, and the specific frequency of LMXBs is proportional to the GC specific luminosity, consistent with the hypothesis that all LMXBs form in GCs.
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Search Results
- 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.
- 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/A+A/595/A35
- Title:
- Low-mass helium white dwarfs evolutionary models
- Short Name:
- J/A+A/595/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A large number of extremely low-mass helium white dwarfs (ELM WDs) have been discovered in recent years. The majority of them are found in close binary systems suggesting they are formed either through a common-envelope phase or via stable mass transfer in a low-mass X-ray binary (LMXB) or a cataclysmic variable (CV) system. Here, we investigate the formation of these objects through the LMXB channel with emphasis on the proto-WD evolution in environments with different metallicities. We study for the first time the combined ects of rotational mixing and element diffusion (e.g. gravitational settling, thermal and chemical diffusion) on the evolution of proto-WDs and on the cooling properties of the resulting WDs. We present state-of-the-art binary stellar evolution models computed with MESA for metallicities of Z=0.02, 0.01, 0.001 and 0.0002, producing WDs with masses between ~0.16-0.45M_{sun}_. Our results confirm that element diffusion plays a significant role in the evolution of proto-WDs that experience hydrogen shell flashes. The occurrence of these flashes produces a clear dichotomy in the cooling timescales of ELM WDs, which has important consequences e.g. for the age determination of binary millisecond pulsars. In addition, we confirm that the threshold mass at which this dichotomy occurs depends on metallicity. Rotational mixing is found to counteract the effect of gravitational settling in the surface layers of young, bloated ELM proto-WDs and therefore plays a key role in determining their surface chemical abundances, i.e. the observed presence of metals in their atmospheres. We predict that these proto-WDs have helium-rich envelopes through a significant part of their lifetime. This is of great importance as helium is a crucial ingredient in the driving of the {kappa}-mechanism suggested for the newly observed ELM proto-WD pulsators. However, we find that the number of hydrogen shell flashes and, as a result, the hydrogen envelope mass at the beginning of the cooling track, are not influenced significantly by rotational mixing. In addition to being dependent on proto-WD mass and metallicity, the hydrogen envelope mass of the newly formed proto-WDs depends on whether or not the donor star experiences a temporary contraction when the H-burning shell crosses the hydrogen discontinuity left behind by the convective envelope. The hydrogen envelope at detachment, although small compared to the total mass of the WD, contains enough angular momentum such that the spin frequency of the resulting WD on the cooling track is well above the orbital frequency.
- ID:
- ivo://CDS.VizieR/J/ApJ/656/437
- Title:
- LS I +61 303 radial velocities and Halpha EW
- Short Name:
- J/ApJ/656/437
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an Halpha monitoring campaign on the BeXRB and microquasar system LS I +61 303. We use radial velocity measurements of HeI lines in our spectra to reevaluate the orbital elements and to better establish the time of periastron. We list equivalent widths and other parameters for the Halpha emission line and discuss the orbital phase related variations observed.
- ID:
- ivo://CDS.VizieR/J/ApJ/656/431
- Title:
- LS I +65 010 radial velocities and Halpha EW
- Short Name:
- J/ApJ/656/431
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a 3yr spectroscopic monitoring program of the Halpha emission in the massive X-ray binary LS I +65 010 = 2S 0114+650, which consists of a B supergiant and a slowly rotating X-ray pulsar. We present revised orbital elements that yield a period of P=11.5983+/-0.0006days and confirm that the orbit has a nonzero eccentricity e=0.18+/-0.05. The Halpha emission profile is formed in the base of the wind of the B supergiant primary, and we show how this spectral feature varies on timescales that are probably related to the rotational period of the B supergiant. We also examine the X-ray fluxes from the Rossi X-ray Timing Explorer All-Sky Monitor instrument, and we show that the X-ray orbital light curve has a maximum at periastron and a minimum at the inferior conjunction of the B supergiant. We also show that the wind emission strength and the high-energy X-ray flux appear to vary in tandem on timescales of approximately 1yr.
- 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/ApJ/896/124
- Title:
- MAXI GSC X-ray LCs of the ULX Swift J0243.6+6124
- Short Name:
- J/ApJ/896/124
- Date:
- 03 Dec 2021 13:33:27
- Publisher:
- CDS
- Description:
- This paper reports on the X-ray emission evolution of the ultraluminous Galactic X-ray pulsar Swift J0243.6+6124 during the giant outburst from 2017 October to 2018 January as observed by the MAXI GSC all-sky survey. The 2-30keV light curve and the energy spectra confirm the source luminosity LX assuming an isotropic emission reached 2.5x10^39^erg/s, 10 times higher than the Eddington limit for a 1.4M_{sun}_ neutron star. When the source was luminous with L_X_>~0.9x10^38^erg/s, it generally exhibited a negative correlation on a hardness-intensity diagram. However, two hardness ratios, a soft color (=4-10keV/2-4keV) and a hard color (=10-20keV/4-10keV), showed somewhat different behavior across a characteristic luminosity of L_c_~5x10^38^erg/s. The soft color changed more than the hard color when L_X_<L_c_, whereas the opposite was observed above Lc. The spectral change above Lc was represented by a broad enhanced feature at ~6keV on top of the canonical cutoff power-law continuum. The pulse profiles, derived daily, made the transition from a single-peak to a double-peak as the source brightened across Lc. These spectral and pulse-shape properties can be interpreted by a scenario in which the accretion columns on the neutron-star surface, producing the Comptonized X-ray emission, gradually became taller as LX increases. The broad 6keV enhancement could be a result of cyclotron-resonance absorption at ~10keV, corresponding to a surface magnetic field B_s_~1.1x10^12^G. The spin-frequency derivatives calculated with the Fermi GBM data showed a smooth positive correlation with LX up to the outburst peak, and its linear coefficient is comparable to those of typical Be binary pulsars whose B_s_ are (1-8)x10^12^G. These results suggest that the B_s_ of Swift J0243.6+6124 is a few times 10^12^G.
- ID:
- ivo://CDS.VizieR/J/MNRAS/415/292
- Title:
- MAXI J1659-152 2010 outburst analysis
- Short Name:
- J/MNRAS/415/292
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive spectral-timing study of the black hole candidate MAXI J1659-152 during its 2010 outburst. We analysed 65 Rossi X-ray timing explorer (RXTE) observations taken along this period, and computed the fundamental diagrams commonly used to study black hole transients. We fitted power density and energy spectra and studied the evolution of the spectral and timing parameters along the outburst. We discuss the evolution of the variability observed at different energy bands on the basis of the relative contribution of the disc and hard components to the energy spectrum of the source.
