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2691. Chandra Typical Galactic Plane Region Point Source Catalog
ID:
ivo://nasa.heasarc/chantypgpr
Title:
Chandra Typical Galactic Plane Region Point Source Catalog
Short Name:
CHANTYPGPR
Date:
28 Feb 2025
Publisher:
NASA/GSFC HEASARC
Description:
Using the Chandra Advanced CCD Imaging Spectrometer Imaging array (ACIS-I), the authors carried out a deep hard X-ray observation of the Galactic plane region at a location (l, b) ~ (28.5 degrees, 0.0 degrees), where no discrete X-ray source had been reported previously. They detected 274 new point X-ray sources (4-sigma or greater confidence in any of the 3 energy bands 0.5 - 3.0 keV, 3.0 - 8.0 keV or 0.5 - 8.0 keV), as well as strong Galactic diffuse emission within two partially overlapping ACIS-I fields (~ 250 square arcminutes in total). The point-source sensitivity was ~ 3 x 10<sup>-15</sup> ergs/s/cm<sup>2</sup> in the 2 - 10 keV band and ~ 2 x 10<sup>-16</sup> erg/s/cm<sup>2</sup> in the 0.5 - 2 keV band The sum of all the detected point-source fluxes accounts for only ~ 10% of the total X-ray flux in the field of view. Only 26 point sources were detected in both the soft and hard bands, indicating that there are two distinct classes of X-ray source distinguished by their spectral hardness ratios. The surface number density of the hard sources is only slightly higher than that measured in high Galactic latitude regions, indicating that the majority of the hard sources are background AGNs. Following up the Chandra observation, the authors performed a near-infrared (NIR) survey with SofI at ESO/NTT. Almost all the soft X-ray sources have been identified in the NIR, and their spectral types are consistent with main-sequence stars, suggesting that most of them are nearby X-ray-active stars. On the other hand, only 22% of the hard sources had near-IR counterparts, which are presumably Galactic. From X-ray and near-IR spectral study, they are most likely to be quiescent cataclysmic variables. This Browse table was created by the HEASARC in December 2006 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/635/214/">CDS Catalog J/ApJ/635/214/</a>, the file table1.dat. This is a service provided by NASA HEASARC .
2692. Chandra ultraluminous X-ray sources
ID:
ivo://CDS.VizieR/J/MNRAS/344/134
Title:
Chandra ultraluminous X-ray sources
Short Name:
J/MNRAS/344/134
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of a Chandra survey of the ultraluminous X-ray sources (ULX) in 13 normal galaxies, in which we combine source detection with X-ray flux measurement. 22 ULX were detected, i.e. with L_X_>10^39^erg/s (L_10_) and 39 other sources were detected with L_X_>5x10^38^erg/s (L_5_). We also use radial intensity profiles to remove extended sources from the sample. The majority of sources are not extended, which for a typical distance constrains the emission region size to less than 50pc. X-ray colour-colour diagrams and spectral fitting results were examined for indicators of the ULX nature. In the case of the brighter sources, spectral fitting generally requires two-component models. In only a few cases do colour-colour diagrams or spectral fitting provide evidence of a black hole nature. We find no evidence of a correlation with stellar mass, however, there is a strong correlation with star formation as indicated by the 60-m flux as found in previous studies.
2693. Chandra variable guide star catalog
ID:
ivo://CDS.VizieR/J/ApJS/188/473
Title:
Chandra variable guide star catalog
Short Name:
J/ApJS/188/473
Date:
21 Oct 2021
Publisher:
CDS
Description:
Variable stars have been identified among the optical-wavelength light curves of guide stars used for pointing control of the Chandra X-ray Observatory. We present a catalog of these variable stars along with their light curves and ancillary data. Variability was detected to a lower limit of 0.02mag amplitude in the 4000-10000{AA} range using the photometrically stable Aspect Camera on board the Chandra spacecraft. The Chandra Variable Guide Star Catalog (VGUIDE) contains 827 stars, of which 586 are classified as definitely variable and 241 are identified as possibly variable. Of the 586 definite variable stars, we believe 319 are new variable star identifications. Types of variables in the catalog include eclipsing binaries, pulsating stars, and rotating stars. The variability was detected during the course of normal verification of each Chandra pointing and results from analysis of over 75000 guide star light curves from the Chandra mission. The VGUIDE catalog represents data from only about 9 years of the Chandra mission. Also, guide stars were often used multiple times for Chandra observations, so many of the stars in the VGUIDE catalog have multiple light curves available from various times in the mission. The catalog is presented as both online data associated with this paper and as a public Web interface. The stars available for use as Chandra guide stars are generally 6-11mag and are commonly spectral types A and later. Statistics of variability compared to spectral type indicate the expected dominance of A-F stars as pulsators. Eclipsing binaries are consistently 20%-30% of the detected variables across all spectral types.
2694. Chandra Variable Guide Star Catalog
ID:
ivo://nasa.heasarc/chanvguide
Title:
Chandra Variable Guide Star Catalog
Short Name:
CHANVGUIDE
Date:
28 Feb 2025
Publisher:
NASA/GSFC HEASARC
Description:
Variable stars have been identified among the optical-wavelength light curves of guide stars used for pointing control of the Chandra X-ray Observatory. The authors present a catalog of these variable stars along with their light curves and ancillary data. Variability was detected to a lower limit of 0.02 mag amplitude in the 4000-10000 Angstroms range using the photometrically stable Aspect Camera on board the Chandra spacecraft. The Chandra Variable Guide Star Catalog (VGUIDE) contains 827 stars, of which 586 are classified as definitely variable and 241 are identified as possibly variable. Of the 586 definite variable stars, the authors believe 319 are new variable star identifications. Types of variables in the catalog include eclipsing binaries, pulsating stars, and rotating stars. The variability was detected during the course of normal verification of each Chandra pointing and results from analysis of over 75,000 guide star light curves from the Chandra mission. The VGUIDE catalog represents data from only about 9 years of the Chandra mission. Future releases of VGUIDE will include newly identified variable guide stars as the mission proceeds. An important advantage of the use of space data to identify and analyze variable stars is the relatively long observations that are available. The Chandra orbit allows for observations up to 2 days in length. Also, guide stars were often used multiple times for Chandra observations, so many of the stars in the VGUIDE catalog have multiple light curves available from various times in the mission. The catalog is presented as both online data associated with this paper (from which this HEASARC representation was created) and as a public Web interface at <a href="http://cxc.harvard.edu/vguide/">http://cxc.harvard.edu/vguide/</a>. Light curves with data at the instrumental time resolution of about 2 s, overplotted with the data binned at 1 ks, can be viewed on the above-mentioned public Web interface and downloaded for further analysis. (This HEASARC Browse table also contains links to these light curves). VGUIDE is a unique project using data collected during the mission that would otherwise be ignored. The stars available for use as Chandra guide stars are generally 6-11 magnitudes and are commonly spectral types A and later. Due to the selection of guide stars entirely for positional convenience, this catalog avoids the possible bias of searching for variability in objects where it is to be expected. Statistics of variability compared to spectral type indicate the expected dominance of A-F stars as pulsators. Eclipsing binaries are consistently 20%-30% of the detected var iables across all spectral types. This table was created by the HEASARC in July 2010 based on the electronic version of Table 4 from the paper which was obtained from the Astrophysical Journal web site. This is a service provided by NASA HEASARC .
2695. Chandra view of the LX-LUV relation in quasars
ID:
ivo://CDS.VizieR/J/A+A/655/A109
Title:
Chandra view of the LX-LUV relation in quasars
Short Name:
J/A+A/655/A109
Date:
22 Feb 2022
Publisher:
CDS
Description:
We present a study of the relation between X-rays and ultraviolet emission in quasars for a sample of broad-line, radio-quiet objects obtained from the cross-match of the Sloan Digital Sky Survey DR14 with the latest Chandra Source Catalog 2.0 (2332 quasars) and the Chandra COSMOS Legacy survey (273 quasars). The non-linear relation between the ultraviolet (at 2500{AA}, LUV) and the X-ray (at 2keV, LX) emission in quasars has been proved to be characterised by a smaller intrinsic dispersion than the observed one, as long as a homogeneous selection, aimed at preventing the inclusion of contaminants in the sample, is fulfilled. By leveraging on the low background of Chandra, we performed a complete spectral analysis of all the data available for the SDSS-CSC2.0 quasar sample (i.e. 3430 X-ray observations), with the main goal of reducing the uncertainties on the source properties (e.g. flux, spectral slope). We analysed whether any evolution of the LX-LUV relation exists by dividing the sample in narrow redshift intervals across the redshift range spanned by our sample, z~=0.5-4. We find that the slope of the relation does not evolve with redshift and it is consistent with the literature value of 0.6 over the explored redshift range, implying that the mechanism underlying the coupling of the accretion disc and hot corona is the same at the different cosmic epochs. We also find that the dispersion decreases when examining the highest redshifts, where only pointed observations are available. These results further confirm that quasars are 'standardisable candles', that is we can reliably measure cosmological distances at high redshifts where very few cosmological probes are available.
2696. Chandra XAssist Source List
ID:
ivo://nasa.heasarc/cxoxassist
Title:
Chandra XAssist Source List
Short Name:
Chan/XAssist
Date:
28 Feb 2025
Publisher:
NASA/GSFC HEASARC
Description:
This database table contains the latest Chandra XAssist source list. XAssist is a NASA-funded project for the automation of X-ray astrophysics, with emphasis on galaxies. It is capable of data reprocessing, source detection, and preliminary spatial, temporal, and spectral analysis for all sources with sufficient counts. The bulk of the system is written in Python, which in turn drives underlying software, e.g., CIAO for Chandra data. Pipelines running on Chandra observations of galaxies have generated the source list which comprises this HEASARC table. The pipeline also includes fields requested by users for various projects, most notably observations of a sample of quasars and several deep field observations have been processed. Note that the pipline processing is completely automated; therefore, users should visually inspect the results of any queries. This table was first created by the HEASARC in May 2005 based on the Chandra source list available at the XAssist website. In September 2010, the HEASARC switched over to using the "pipeline4" Chandra source list. It is updated on a weekly basis when and if the XAssist source list file at <a href="https://asd.gsfc.nasa.gov/xassist/pipeline4/chandra/master_srclist.csv">https://asd.gsfc.nasa.gov/xassist/pipeline4/chandra/master_srclist.csv</a> is updated. This is a service provided by NASA HEASARC .
2697. Chandra X-Ray Binary Catalog of SINGS Galaxies
ID:
ivo://nasa.heasarc/changalxrb
Title:
Chandra X-Ray Binary Catalog of SINGS Galaxies
Short Name:
CHANGALXRB
Date:
28 Feb 2025
Publisher:
NASA/GSFC HEASARC
Description:
The authors of this catalog presented new Chandra constraints on the X-ray luminosity functions (XLFs) of X-ray binary (XRB) populations, as well as their scaling relations, for a sample of 38 nearby galaxies (D = 3.4-29 Mpc). The galaxy sample is drawn primarily from the Spitzer Infrared Nearby Galaxies Survey (SINGS) and contains a wealth of Chandra (5.8 Ms total) and multiwavelength data, allowing for star formation rates (SFRs) and stellar masses (M<sub>*</sub>) to be measured on subgalactic scales. The authors divided the 2478 X-ray-detected sources into 21 subsamples in bins of specific SFR (sSFR=SFR/M<sub>*</sub>) and constructed XLFs. To model the XLF dependence on sSFR, they fitted a global XLF model, containing contributions from high-mass XRBs (HMXBs), low-mass XRBs (LMXBs), and background sources from the cosmic X-ray background that respectively scale with SFR, M<sub>*</sub>, and sky area. They found an HMXB XLF that is more complex in shape than previously reported and an LMXB XLF that likely varies with sSFR, potentially due to an age dependence. When applying the global model to XLF data for each individual galaxy, the authors discovered a few galaxy XLFs that significantly deviated from their model beyond statistical scatter. Most notably, relatively low-metallicity galaxies have an excess of HMXBs above ~10<sup>38</sup>erg/s, and elliptical galaxies that have relatively rich populations of globular clusters (GCs) show excesses of LMXBs compared to the global model. Additional modeling of how the XRB XLF depends on stellar age, metallicity, and GC specific frequency is required to sufficiently characterize the XLFs of galaxies. In this work, the authors utilized 5.8 Ms of Chandra ACIS data, combined with UV-to-IR observations, for 38 nearby (D < ~30 Mpc) Spitzer Infrared Nearby Galaxies Survey (SINGS; Kennicutt+ <a href="https://ui.adsabs.harvard.edu/abs/2003PASP..115..928K">2003PASP..115..928K</a>) galaxies to revisit scaling relations of the HMXB and LMXB X-ray luminosity functions (XLFs) with SFR and M<sub>*</sub>, respectively. This table contains the X-ray properties for 4442 X-ray point sources, including those with L<sub>X</sub> < 10<sup>35</sup>erg/s, which were excluded from the XLF analysis. This table was created by the HEASARC in April 2023 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/243/3">CDS Catalog J/ApJS/243/3</a> file table7.dat. This is a service provided by NASA HEASARC .
2698. Chandra X-ray detection of YSOs in Serpens South
ID:
ivo://CDS.VizieR/J/AJ/155/241
Title:
Chandra X-ray detection of YSOs in Serpens South
Short Name:
J/AJ/155/241
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a Chandra study of the deeply embedded Serpens South star-forming region, examining cluster structure and disk properties at the earliest stages. In total, 152 X-ray sources are detected. Combined with Spitzer and 2MASS photometry, 66 X-ray sources are reliably matched to an IR counterpart. We identify 21 class I, 6 flat spectrum, 16 class II, and 18 class III young stars; 5 were unclassified. Eighteen sources were variable in X-rays, 8 exhibiting flare-like emission and one source being periodic. The cluster's X-ray luminosity distance was estimated: the best match was to the nearer distance of 260 pc for the front of the Aquila Rift complex. The ratio of N_H_ to A_K_ is found to be ~0.68x10^22^, similar to that measured in other young low-mass regions, but lower than that measured in the interstellar medium and high-mass clusters (~(1.6-2)x10^22^). We find that the spatial distribution closely follows that of the dense filament from which the stars have formed, with the class II population still strongly associated with the filament. There are four subclusters in the field, with three forming knots in the filament, and a fourth to the west, which may not be associated but may be contributing to the distributed class III population. A high percentage of diskless class IIIs (upper limit 30% of classified X-ray sources) in such a young cluster could indicate that processing of disks is influenced by the cluster environment and is not solely dependent on timescale.
2699. Chandra X-ray flares in rho Ophiuchi
ID:
ivo://CDS.VizieR/J/PASJ/55/653
Title:
Chandra X-ray flares in rho Ophiuchi
Short Name:
J/PASJ/55/653
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the {rho} Ophiuchi star-forming cloud. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares.
2700. Chandra X-Ray galaxy clusters at z <1.4
ID:
ivo://CDS.VizieR/J/AZh/91/679
Title:
Chandra X-Ray galaxy clusters at z <1.4
Short Name:
J/AZh/91/679
Date:
21 Oct 2021
Publisher:
CDS
Description:
A reconstruction of the total mass (the fraction of dark matter, intercluster gas, and the brightest galaxy of the cluster) of 128 X-ray galaxy clusters at redshifts 0.01-1.4 based on Chandra observations is presented. The total mass M200 and the baryonic mass Mb have been measured for all the sample objects, as well as the concentration parameter c200, which characterizes the size of the dark matter halo. The existence of a tight correlation between c200 and M200 is confirmed, c{prop.to}M^a^_vir_/(1+z)b with a=-0.56+/-0.15 and b=0.80+/-0.25 (95% confidence level), in good agreement with the predictions of numerical simulations and previous observations. Fitting the inner dark-matter density slope {alpha} with a generalized NFW model yields {alpha}=1.10+/-0.48 at the 2{sigma} confidence level, combining the results for the entire sample, for which the model gives a good description of the data. There is also a tight correlation between the inner slope of the dark-matter density profile {alpha} and the baryonic mass contentMb for massive galaxy clusters, namely, {alpha} decreases with increasing baryonic mass content. A simple power-law model is used to fit the {alpha}-M_b_ distributions, yielding the break point for the inner slope of the dark-matter density profile b=1.72+/-0.37 (68% confidence level).

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