- ID:
- ivo://CDS.VizieR/J/ApJ/687/1019
- Title:
- Chandra X-ray observations of M71
- Short Name:
- J/ApJ/687/1019
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observe the nearby, low-density globular cluster M71 (NGC 6838) with the Chandra X-Ray Observatory to study its faint X-ray populations. Five X-ray sources are found inside the cluster core radius, including the known eclipsing binary millisecond pulsar (MSP) PSR J1953+1846A. The X-ray light curve of the source coincident with this MSP shows marginal evidence for periodicity at the binary period of 4.2hr. Its hard X-ray spectrum and luminosity resemble those of other eclipsing binary MSPs in 47 Tuc, suggesting a similar shock origin of the X-ray emission. A further 24 X-ray sources are found within the half-mass radius, reaching to a limiting luminosity of 1.5x10^30^ergs/s (0.3-8keV). From a radial distribution analysis, we find that 18+/-6 of these 29 sources are associated with M71, somewhat more than predicted, and that 11+/-6 are background sources, both Galactic and extragalactic. M71 appears to have more X-ray sources in the range L_X_=10^30^-10^31^ergs/s than expected by extrapolating from other studied clusters using either mass or collision frequency. We explore the spectra and variability of these sources and describe the results of ground-based optical counterpart searches.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/586/826
- Title:
- Chandra X-ray observations of NGC 1316
- Short Name:
- J/ApJ/586/826
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of the Chandra ACIS subarcsecond resolution X-ray observation of the archetypal merger radio galaxy NGC 1316 (Fornax A).
- ID:
- ivo://CDS.VizieR/J/ApJ/588/1009
- Title:
- Chandra X-ray observations of NGC 2516
- Short Name:
- J/ApJ/588/1009
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive study of the Chandra X-ray observations of the young open cluster NGC 2516. We have analyzed eight individual Chandra observations. We have combined the data to achieve the greatest sensitivity, reaching down to log f_X_=-14.56(erg/s/cm^2^), or logLX=28.69(erg/s) at the distance of NGC 2516. Out of 284 X-ray sources detected, 155 are identified with photometric cluster members, with very little ambiguity.
- ID:
- ivo://CDS.VizieR/J/ApJ/598/375
- Title:
- Chandra X-ray observations of NGC 2024
- Short Name:
- J/ApJ/598/375
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a sensitive 76ks Chandra observation of the young stellar cluster in NGC 2024, lying at a distance of ~415pc in the Orion B giant molecular cloud. Previous infrared observations have shown that this remarkable cluster contains several hundred embedded young stars, most of which are still surrounded by circumstellar disks. Thus, it presents a rare opportunity to study X-ray activity in a large sample of optically invisible protostars and classical T Tauri stars (CTTSs) undergoing accretion. Chandra detected 283 X-ray sources, of which 248 were identified with counterparts at other wavelengths, mostly in the near-infrared. Astrometric registration of Chandra images against the Two Micron All Sky Survey (2MASS) resulted in positional offsets of ~0.25" near field center, yielding high confidence identifications of infrared counterparts.
- ID:
- ivo://CDS.VizieR/J/ApJ/746/54
- Title:
- Chandra X-ray observations of SDSS-DR5 QSOs
- Short Name:
- J/ApJ/746/54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the X-ray variability of 264 Sloan Digital Sky Survey spectroscopic quasars using the Chandra public archive. This data set consists of quasars with spectroscopic redshifts out to z {approx} 5 and covers rest-frame timescales up to {Delta}t_sys_{approx} 2000 days, with three or more X-ray observations available for 82 quasars. It therefore samples longer timescales and higher luminosities than previous large-scale analyses of active galactic nucleus (AGN) variability. We find significant ( >~ 3{sigma}) variation in {approx}30% of the quasars overall; the fraction of sources with detected variability increases strongly with the number of available source counts up to {approx}70% for sources with >= 1000 counts per epoch. Assuming that the distribution of fractional variation is Gaussian, its standard deviation is {approx}16% on >~ 1 week timescales, which is not enough to explain the observed scatter in quasar X-ray-to-optical flux ratios as being due to variability alone. We find no evidence in our sample that quasars are more variable at higher redshifts (z > 2), as has been suggested in previous studies. Quasar X-ray spectra vary similarly to some local Seyfert AGNs in that they steepen as they brighten, with evidence for a constant, hard spectral component that is more prominent in fainter stages. We identify one highly variable Narrow Line Seyfert 1-type spectroscopic quasar in the Chandra Deep Field-North. We constrain the rate of kilosecond-timescale flares in the quasar population using {approx}8 months of total exposure and also constrain the distribution of variation amplitudes between exposures; extreme changes (>100%) are quite rare, while variation at the 25% level occurs in <25% of observations. [O III] {lambda}5007 {AA} emission may be stronger in sources with lower levels of X-ray variability; if confirmed, this would represent an additional link between small-scale (corona) and large-scale (narrow-line region) AGN properties.
- ID:
- ivo://cxc.harvard.edu/cda
- Title:
- Chandra X-ray Observatory Data Archive
- Short Name:
- CDA
- Date:
- 18 Jul 2019
- Publisher:
- Chandra X-ray Observatory
- Description:
- The Chandra X-ray Observatory is the U.S. follow-on to the Einstein Observatory. Chandra was formerly known as AXAF, the Advanced X-ray Astrophysics Facility, but renamed by NASA in December, 1998. Originally three instruments and a high-resolution mirror carried in one spacecraft, the project was reworked in 1992 and 1993. The Chandra spacecraft carries a high resolution mirror, two imaging detectors, and two sets of transmission gratings. Important Chandra features are: an order of magnitude improvement in spatial resolution, good sensitivity from 0.1 to 10 keV, and the capability for high spectral resolution observations over most of this range.
- ID:
- ivo://CDS.VizieR/J/ApJS/238/23
- Title:
- Chandra X-ray point sources in Abell 133
- Short Name:
- J/ApJS/238/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As an evolutionary phase of galaxies, active galactic nuclei (AGNs) over a large range of redshifts have been utilized for understanding cosmic evolution. In particular, the population and evolution of AGNs have been investigated through the study of the cosmic X-ray background in various fields. As one of the deep fields observed by Chandra, with a total of 2.8Ms exposures, Abell 133 is a special region for investigating AGNs, providing a testbed for probing the environmental effects on AGN triggers, since cluster environments can be different from field environments. The achieved flux limits of data at the 50% completeness levels of 6.95x10^-16^, 1.43x10^-16^, and 1.57x10^-15^erg/s/cm^2^ are 0.5-8, 0.5-2, and 2-8keV. Using the wavdetect and no-source binomial probability (i.e., p<0.007), we analyze the combined Chandra image, detecting 1617 (in 0.5-8keV), 1324 (in 0.5-2keV), and 1028 (in 2-8keV) X-ray point sources in the Abell 133 region. Here, we present the X-ray point source catalog with the source fluxes, which can be combined with multiwavelength data for future works. We find that the number count distribution of the X-ray point sources is well reproduced with a broken power-law model, while the best-fit model parameters are sensitive to the fitting range of the number count distribution. Finally, we find an excess of number density (a decrease of AGN fraction) at the central region of the cluster, which reflects the effect of dense environments on AGN triggers, a finding similar to those of other studies of galaxy clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/560/675
- Title:
- Chandra X-ray point sources in Cen A
- Short Name:
- J/ApJ/560/675
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from two Chandra X-ray Observatory observations of the X-ray point source population in the nearby radio galaxy Centaurus A (NGC 5128). Using a wavelet decomposition detection algorithm, we detect 246 individual point sources above a limiting luminosity of ~2*10^36^ergs/s, 82 of which are detected in both data sets where the fields of view overlap. Thirty-eight sources were detected in only one observation but were within the field of view of both pointings, implying considerable variability. We identify eight foreground stars in our observations. We also identify nine of the sources with known globular clusters in Centaurus A. All previously observed ROSAT sources within our field of view are detected.
- ID:
- ivo://CDS.VizieR/J/A+A/447/71
- Title:
- CHANDRA X-ray point sources in Cen A (NGC 5128)
- Short Name:
- J/A+A/447/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have studied the X-ray point source population of Centaurus A (NGC 5128) using data from four archival CHANDRA observations. We detected 272 point-like X-ray sources within a radius of 10' from the centre. Approximately half of these are CXB sources, with the remaining half being LMXBs. The spatial distribution of the LMXBs, both azimuthally averaged and 2D, is consistent with the distribution of the K-band light observed in the 2MASS survey. After correction for the incompleteness effect we constrain the LMXB luminosity function down to ~2x10^36^erg/s, much lower than previous studies of LMXBs in elliptical galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/602/231
- Title:
- Chandra X-ray point sources in nearby galaxies
- Short Name:
- J/ApJ/602/231
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed Chandra ACIS observations of 32 nearby spiral and elliptical galaxies and present the results of 1441 X-ray point sources that were detected in these galaxies. The total point-source X-ray (0.3-8.0keV) luminosity L_XP_ is well correlated with the B-band, K-band, and FIR+UV luminosities of spiral host galaxies and is well correlated with the B-band and K-band luminosities of elliptical galaxies. This suggests an intimate connection between L_XP_ and both the old and young stellar populations, for which K and FIR+UV luminosities are reasonable proxies for the galaxy mass M and star formation rate SFR.