- ID:
- ivo://CDS.VizieR/J/ApJ/664/458
- Title:
- Spectral fit of ULX sources
- Short Name:
- J/ApJ/664/458
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Data from Chandra observations of 30 nearby galaxies were analyzed and 365 X-ray point sources were chosen whose spectra were not contaminated by excessive diffuse emission and not affected by photon pileup. The spectra of these sources were fitted using two spectral models (an absorbed power-law and a disk blackbody) to ascertain the dependence of estimated parameters on the spectral model used. It was found that the cumulative luminosity function depends on the choice of the spectral model, especially for luminosities >10^40^ergs/s. A large number (~80) of the sources have luminosities >10^39^ergs/s (ultraluminous X-ray sources) with indistinguishable average spectral parameters (inner disk temperature ~1keV and/or photon index GAMMA~2) with those of the lower luminosity ones.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/682/821
- Title:
- Spectral fits of galaxy clusters in X-ray
- Short Name:
- J/ApJ/682/821
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the band dependence of the inferred X-ray temperature of the intracluster medium (ICM) for 192 well-observed galaxy clusters selected from the Chandra Data Archive. If the hot ICM is nearly isothermal in the projected region of interest, the X-ray temperature inferred from a broadband (0.7-7.0keV) spectrum should be identical to the X-ray temperature inferred from a hard-band (2.0-7.0keV) spectrum. However, if unresolved cool lumps of gas are contributing soft X-ray emission, the temperature of a best-fit single-component thermal model will be cooler for the broadband spectrum than for the hard-band spectrum. Using this difference as a diagnostic, the ratio of best-fitting hard-band and broadband temperatures may indicate the presence of cooler gas even when the X-ray spectrum itself may not have sufficient signal-to-noise ratio (S/N) to resolve multiple temperature components. To test this possible diagnostic, we extract X-ray spectra from core-excised annular regions for each cluster in our archival sample. We compare the X-ray temperatures inferred from single-temperature fits when the energy range of the fit is 0.7-7.0keV (broad) and when the energy range is 2.0/(1+z)-7.0keV (hard). We find that the hard-band temperature is significantly higher, on average, than the broadband temperature. On further exploration, we find this temperature ratio is enhanced preferentially for clusters which are known merging systems. In addition, cool-core clusters tend to have best-fit hard-band temperatures that are in closer agreement with their best-fit broadband temperatures. We show, using simulated spectra, that this diagnostic is sensitive to secondary cool components (T_X_=0.5-3.0keV) with emission measures >=10-30% of the primary hot component.
- 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/MNRAS/448/1541
- Title:
- Spectral parameters for Mrk 335 and Ark 564
- Short Name:
- J/MNRAS/448/1541
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive flux-resolved spectral analysis of the bright narrow-line Seyfert 1 AGNs, Mrk 335 and Ark 564 using observations by XMM-Newton satellite. The mean and the flux-resolved spectra are fitted by an empirical model consisting of two Comptonization components, one for the low-energy soft excess and the other for the high-energy power law. A broad iron line and a couple of low-energy edges are required to explain the spectra. For Mrk 335, the 0.3-10 keV luminosity relative to the Eddington value, L_X_/L_Edd_, varied from 0.002 to 0.06. The index variation can be empirically described as {Gamma}=0.6log_10_L_X_/L_Edd_+3.0 for 0.005<L_X_/L_Edd_<0.04. At L_X_/L_Edd_~0.04 the spectral index changes and then continues to follow {Gamma}=0.6log_10_L_X_/L_Edd_+2.7, i.e. on a parallel track. We confirm that the result is independent of the specific spectral model used by fitting the data in the 3-10 keV band by only a power law and an iron line. For Ark 564, the index variation can be empirically described as {Gamma}=0.2log_10_L_X_/L_Edd_+2.7 with a significantly large scatter as compared to Mrk 335. Our results indicate that for Mrk 335, there may be accretion disc geometry changes which lead to different parallel tracks. These changes could be related to structural changes in the corona or enhanced reflection at high flux levels. There does not seem to be any homogeneous or universal relationship for the X-ray index and luminosity for different AGNs or even for the same AGN.
- ID:
- ivo://CDS.VizieR/J/ApJS/232/17
- Title:
- Spectral properties of magnetar bursts
- Short Name:
- J/ApJS/232/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our broadband (2-250keV) time-averaged spectral analysis of 388 bursts from SGR J1550-5418, SGR 1900+14, and SGR 1806-20 detected with the Rossi X-ray Timing Explorer (RXTE) here and as a database in a companion web-catalog. We find that two blackbody functions (BB+BB), the sum of two modified blackbody functions (LB+LB), the sum of a blackbody function and a power-law function (BB+PO), and a power law with a high-energy exponential cutoff (COMPT) all provide acceptable fits at similar levels. We performed numerical simulations to constrain the best fitting model for each burst spectrum and found that 67.6% of burst spectra with well-constrained parameters are better described by the Comptonized model. We also found that 64.7% of these burst spectra are better described with the LB+LB model, which is employed in the spectral analysis of a soft gamma repeater (SGR) for the first time here, than with the BB+BB and BB+PO models. We found a significant positive lower bound trend on photon index, suggesting a decreasing upper bound on hardness, with respect to total flux and fluence. We compare this result with bursts observed from SGR and AXP (anomalous X-ray pulsar) sources and suggest that the relationship is a distinctive characteristic between the two. We confirm a significant anticorrelation between burst emission area and blackbody temperature, and find that it varies between the hot and cool blackbody temperatures differently than previously discussed. We expand on the interpretation of our results in the framework of a strongly magnetized neutron star.
- ID:
- ivo://CDS.VizieR/J/A+A/285/812
- Title:
- Spectral properties of X-ray extragal. sources
- Short Name:
- J/A+A/285/812
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/434/54
- Title:
- Spectral properties of X-ray-selected AGNs
- Short Name:
- J/ApJ/434/54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We survey the broadband spectral properties of ~500 X-ray-selected active galactic nuclei (AGNs) observed with the Einstein Observatory. Included in this survey are the ~450 AGNs in the Extended Medium Sensitivity Survey of Gioia et al. (1990ApJS...72..567G) and the ~50 AGNs in the Ultrasoft Survey of Cordova et al. (1992ApJS...81..661C). We present a revised version of the latter sample, based on the post publication discovery of a software error in the Einstein Rev-1b processing. We find that the mean spectral index of the AGNs between 0.1 and 0.6keV is softer, and the distribution of indices wider, than previous estimates based on analyses of the X-ray spectra of optically selected AGNs. A subset of these AGNs exhibit flux variability, some on timescales as short as 0.05-days. A correlation between radio and hard X-ray luminosity is confirmed, but the data do not support a correlation between the radio and soft X-ray luminosities, or between radio loudness and soft X-ray spectral slope. Evidence for physically distinct soft and hard X-ray components is found, along with the possibility of a bias in previous optically selected samples toward selection of AGNs with flatter X-ray spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A67
- Title:
- Spectra of 75 Swift/BAT optical counterparts
- Short Name:
- J/A+A/561/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Through an optical campaign performed at four telescopes located in the northern and the southern hemispheres, we obtained optical spectroscopy for 75 counterparts of unclassified or poorly studied hard X-ray emitting objects detected with Swift/Burst Alert Telescope (BAT) and listed in the 54 month Palermo catalogue. All these objects also have observations taken with Swift/X-ray Telescope (XRT) or Chandra satellites, which allowed us to reduce the high-energy error box and pinpoint the most likely optical counterparts.
- ID:
- ivo://CDS.VizieR/J/A+A/545/A101
- Title:
- Spectra of 29 Swift/BAT optical counterparts
- Short Name:
- J/A+A/545/A101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Through an optical campaign performed at four telescopes located in the northern and the southern hemispheres, plus archival data from two on-line sky surveys, we obtained optical spectroscopy for 29 counterparts of unclassified or poorly studied hard X-ray emitting objects detected with Swift/Burst Alert Telescope (BAT) and listed in the 39 month Palermo catalogue. All these objects also have observations taken with Swift/X-ray Telescope (XRT) or XMM-European Photon Imaging Camera (EPIC) which not only allow us to pinpoint their optical counterpart, but also study their X-ray spectral properties (column density, power law photon index, and F2-10keV flux).
- ID:
- ivo://CDS.VizieR/J/A+A/433/151
- Title:
- Spectrocopic results on ROSAT late-type stars
- Short Name:
- J/A+A/433/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of an investigation of the X-ray properties, age distribution, and kinematical characteristics of a high-galactic latitude sample of late-type field stars selected from the ROSAT All-Sky Survey (RASS). The sample comprises 254 RASS sources with optical counterparts of spectral types F to M distributed over six study areas located at |b|>~20{deg}, and Dec>=-9{deg}. A detailed study was carried out for the subsample of ~200 G, K, and M stars. Lithium abundances were determined for 179 G-M stars. Radial velocities were measured for most of the 141 G and K type stars of the sample. Combined with proper motions these data were used to study the age distribution and the kinematical properties of the sample. Based on the lithium abundances half of the G-K stars were found to be younger than the Hyades (660Myr). About 25% are comparable in age to the Pleiades (100Myr). A small subsample of 10 stars is younger than the Pleiades. They are therefore most likely pre-main sequence stars. Kinematically the PMS and Pleiades-type stars appear to form a group with space velocities close to the Castor moving group but clearly distinct from the Local Association.