- ID:
- ivo://CDS.VizieR/J/MNRAS/462/4371
- Title:
- Sample of faint X-ray pulsators
- Short Name:
- J/MNRAS/462/4371
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the discovery of 41 new pulsating sources in the data of the Chandra Advanced CCD Imaging Spectrometer, which is sensitive to X-ray photons in the 0.3-10 keV band. The archival data of the first 15 yr of Chandra observations were retrieved and analysed by means of fast Fourier transforms, employing a peak-detection algorithm able to screen candidate signals in an automatic fashion. We carried out the search for new X-ray pulsators in light curves with more than 50 photons, for a total of about 190000 light curves out of about 430000 extracted. With these numbers, the ChAndra Timing Survey at Brera And Roma astronomical observatories (CATS @ BAR) - as we called the project - represents the largest ever systematic search for coherent signals in the classic X-ray band. More than 50 per cent of the signals were confirmed by further Chandra (for those sources with two or more pointings), XMM-Newton or ROSAT data. The period distribution of the new X-ray pulsators above ~2000s resembles that of cataclysmic variables, while there is a paucity of sources with shorter period and low fluxes. Since there is not an obvious bias against these detections, a possible interpretation is in terms of a magnetic gating mechanism in accreting neutron stars. Finally, we note that CATS @ BAR is a living project and the detection algorithm will continue to be routinely applied to the new Chandra data as they become public. Based on the results obtained so far, we expect to discover about three new pulsators every year.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/687/1230
- Title:
- SFXTs observed by Swift. I. Outside outbursts
- Short Name:
- J/ApJ/687/1230
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Supergiant fast X-ray transients (SFXTs) are a new class of high-mass X-ray binaries (HMXBs) discovered thanks to the monitoring of the Galactic plane performed with the INTEGRAL satellite in the last 5 years. To characterize the properties of these sources on timescales of months, we are performing a monitoring campaign with Swift of four SFXTs (IGR J16479-4514, XTE J1739-302, IGR J17544-2619, and AX J1841.0-0536/IGR J18410-0535). We report on the first 4 months of Swift observations, which started on 2007 October 26. We detect low-level X-ray activity in all four SFXTs, which demonstrates that these transient sources accrete matter even outside their outbursts. The X-ray spectra are typically hard, with an average 2-10keV luminosity during this monitoring of about 10^33^-10^34^erg/s. We detected pulsations from the pulsar AX J1841.0-0536/IGR J18410-0535, with a period of 4.7008+/-0.0004s.
- ID:
- ivo://CDS.VizieR/J/A+A/467/585
- Title:
- Sources detected by ISGRI
- Short Name:
- J/A+A/467/585
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In its first 4 years of observing the sky above 20keV, INTEGRAL-ISGRI has detected 500 sources, around half of which are new or unknown at these energies. Follow-up observations at other wavelengths revealed that some of these sources feature unusually large column densities, long pulsations, and other interesting characteristics. We investigate where new and previously-known sources detected by ISGRI fit in the parameter space of high-energy objects, and we use the parameters to test correlations expected from theoretical predictions. For example, the influence of the local absorbing matter on periodic modulations is studied for Galactic High-Mass X-ray Binaries (HMXBs) with OB supergiant and Be companions. We examine the spatial distribution of different types of sources in the Milky Way using various projections of the Galactic plane, in order to highlight signatures of stellar evolution and to speculate on the origin of the group of sources whose classifications are still uncertain.
- ID:
- ivo://CDS.VizieR/J/ApJ/853/150
- Title:
- Spectral analysis of low-mass X-ray binaries
- Short Name:
- J/ApJ/853/150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A recent study of a small sample of X-ray binaries (XRBs) suggests a significant softening of spectra of neutron star (NS) binaries as compared to black hole (BH) binaries in the luminosity range 10^34^-10^37^erg/s. This softening is quantified as an anticorrelation between the spectral index and the 0.5-10keV X-ray luminosity. We extend the study to significantly lower luminosities (i.e., ~a few x10^30^erg/s) for a larger sample of XRBs. We find evidence for a significant anticorrelation between the spectral index and the luminosity for a group of NS binaries in the luminosity range 10^32^-10^33^erg/s. Our analysis suggests a steep slope for the correlation i.e., -2.12+/-0.63. In contrast, BH binaries do not exhibit the same behavior. We examine the possible dichotomy between NS and BH binaries in terms of a Comptonization model that assumes a feedback mechanism between an optically thin hot corona and an optically thick cool source of soft photons. We gauge the NS-BH dichotomy by comparing the extracted corona temperatures, Compton-y parameters, and the Comptonization amplification factors: the mean temperature of the NS group is found to be significantly lower than the equivalent temperature for the BH group. The extracted Compton-y parameters and the amplification factors follow the theoretically predicted relation with the spectral index.
- ID:
- ivo://CDS.VizieR/J/A+A/542/A56
- Title:
- Spectral analysis of 2010-11 outburst of GX 339-4
- Short Name:
- J/A+A/542/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic transient black hole candidate (BHC) GX 339-4 exhibited several outbursts at regular intervals of about two to three years in the Rossi X-ray Timing Explorer (RXTE) era. After remaining in an almost quiescent state for three long years, it again became X-ray active in January, 2010, continuing to be so over the next ~14 months. We study the timing and spectral properties of the BHC during its recent outburst and understand the behavioral change in the accretion flow dynamics associated with the evolution of the various X-ray features. The detailed analysis of the temporal and spectral properties of the source during this outburst are carried out using archival data of the RXTE PCA instrument. We analyze a total of 236 observational intervals consisting of 419 days of data observed by RXTE, from 2010 January 12 to 2011 March 6.
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/4735
- Title:
- Spectral evolution of 4U 1543-47 in 2002
- Short Name:
- J/MNRAS/468/4735
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the viscous evolution of the accretion disc in 4U 1543-47, a black hole binary system, during the first 30 d after the peak of the 2002 burst by comparing the observed and theoretical accretion rate evolution dM(t)/dt. The observed dM(t)/dt is obtained from spectral modelling of the archival Proportional Counter Array aboard the RXTE observatory (RXTE/PCA) data. Different scenarios of disc decay evolution are possible depending on a degree of self-irradiation of the disc by the emission from its centre. If the self-irradiation, which is parametrized by factor C_irr_, had been as high as ~5x10^-3^, then the disc would have been completely ionized up to the tidal radius and the short time of the decay would have required the turbulent parameter {alpha}~3. We find that the shape of the \dot M(t) curve is much better explained in a model with a shrinking high-viscosity zone. If C_irr_~(2-3)x10^-4^, the resulting {alpha} lie in the interval 0.5-1.5 for the black hole masses in the range 6-10M_{sun}_, while the radius of the ionized disc is variable and controlled by irradiation. For very weak irradiation, C_irr_<1.5x10^-4^, the burst decline develops as in normal outbursts of dwarf novae with {alpha}~0.08-0.32. The optical data indicate that C_irr_ in 4U 1543-47 (2002) was not greater than approximately (3-6)x10^-4^. Generally, modelling of an X-ray nova burst allows one to estimate {alpha} that depends on the black hole parameters. We present the public 1D code FREDDI to model the viscous evolution of an accretion disc. Analytic approximations are derived to estimate {alpha} in X-ray novae using dM(t)/dt.
- ID:
- ivo://CDS.VizieR/J/MNRAS/422/679
- Title:
- Spectral parameters for MAXI J1543-564
- Short Name:
- J/MNRAS/422/679
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a spectral-timing analysis of the black hole X-ray binary candidate MAXI J1543-564 during its 2011 outburst. All 99 pointed observations of this outburst obtained with the Rossi X-ray Timing Explorer (RXTE) were included in our study. We computed the fundamental diagrams commonly used to study black hole transients, and fitted power density and energy spectra to study the spectral and timing parameters along the outburst. The determination of timing parameters and hence of exact transitions between different states was hampered by the rather low count rate at which this outburst was observed. We detected two periods of exponential decay, one after the source was brightest, which was interrupted by several flares, and another one during the high soft state. The detection of these decays allowed us to obtain an estimate for the source distance of at least 8.5kpc. This leaves two possible explanations for the observed low count rate; either the source has a distance similar to that of other black hole X-ray binary candidates and it is intrinsically faint, or it has a similar luminosity, but is located more than 12 kpc away from us. Furthermore, in the high/soft state the source spectrum appears to be completely disc dominated.
- ID:
- ivo://CDS.VizieR/J/A+A/590/A122
- Title:
- Spectra of high-mass X-ray binaries
- Short Name:
- J/A+A/590/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-mass X-ray binaries are bright X-ray sources. The high-energy emission is caused by the accretion of matter from the massive companion onto a neutron star. The accreting material comes from either the strong stellar wind in binaries with supergiant companions or the circumstellar disk in Be/X-ray binaries. In either case, the H{alpha} line stands out as the main source of information about the state of the accreting material. We present the results of our monitoring program to study the long-term variability of the H{alpha} line in high-mass X-ray binaries. Our aim is to characterise the optical variability timescales and study the interaction between the neutron star and the accreting material. We fitted the H{alpha} line with Gaussian profiles and obtained the line parameters and equivalent width. The peak separation in split profiles was used to determine the disk velocity law and estimate the disk radius. The relative intensity of the two peaks (V/R ratio) allowed us to investigate the distribution of gas particles in the disk. The equivalent width was used to characterise the degree of variability of the systems. We also studied the variability of the H{alpha} line in correlation with the X-ray activity.
- ID:
- ivo://CDS.VizieR/J/ApJ/660/1398
- Title:
- Spectro. monitoring of HDE 245770 and X Per
- Short Name:
- J/ApJ/660/1398
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from an H{alpha} monitoring campaign of the Be X-ray binary systems HDE 245770 = A0535+26 and X Per. We use the H{alpha} equivalent widths together with adopted values of the Be star effective temperature, disk inclination, and disk outer boundary to determine the half-maximum emission radius of the disk as a function of time.
- ID:
- ivo://CDS.VizieR/J/A+A/484/783
- Title:
- Spectroscopy of 7 INTEGRAL X-ray sources
- Short Name:
- J/A+A/484/783
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The INTEGRAL hard X-ray observatory has revealed an emerging population of highly obscured X-ray binary systems through multi-wavelength observations. Previous studies have shown that many of these sources are high-mass X-ray binaries hosting neutron stars orbiting around luminous and evolved companion stars. To better understand this newly-discovered population, we have selected a sample of sources for which an accurate localisation is available to identify the stellar counterpart and reveal the nature of the companion star and of the binary system.
