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2701. Chandra X-ray observation of Gum 31
ID:
ivo://CDS.VizieR/J/A+A/564/A120
Title:
Chandra X-ray observation of Gum 31
Short Name:
J/A+A/564/A120
Date:
21 Oct 2021
Publisher:
CDS
Description:
Gum 31 is a prominent, but still rather poorly studied HII region around the stellar cluster NGC 3324 at the northwestern periphery of the Carina nebula complex. Our aim was to reveal and characterize the young stellar population in Gum 31. An X-ray survey is the only efficient way to identify young stars in this region with extremely high galactic field-star contamination that can avoid the strong biases of infrared excess selected samples of disk-bearing young stars. We used the Chandra observatory to perform a deep (70ks) X-ray observation of the Gum 31 region and detected 679 X-ray point sources. This extends and complements the X-ray survey of the central Carina nebula regions performed in the Chandra Carina Complex Project (CCCP). Using deep near-infrared images from our recent VISTA survey of the Carina nebula complex, our comprehensive Spitzer point-source catalog, and optical archive data, we identify counterparts for 75% of these X-ray sources.
2702. Chandra X-ray observations in Eagle Nebula. I.
ID:
ivo://CDS.VizieR/J/ApJ/654/347
Title:
Chandra X-ray observations in Eagle Nebula. I.
Short Name:
J/ApJ/654/347
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present and analyze the first high-resolution X-ray images ever obtained of the Eagle Nebula star-forming region. On 2001 July 30 the Chandra X-Ray Observatory obtained a 78ks image of the Eagle Nebula (M16) that includes the core of the young galactic cluster NGC 6611 and the dark columns of dust and cold molecular gas in M16 known as the "Pillars of Creation". We find a total of 1101 X-ray sources in the 17'x17' ACIS-I field of view. Most of the X-ray sources are low-mass pre-main-sequence or high-mass main-sequence stars in this young cluster. A handful of hard X-ray sources in the pillars are spatially coincident with deeply embedded young stellar objects seen in high-resolution near-infrared images recently obtained with the VLT (McCaughrean & Andersen, 2002A&A...389..513M). In this paper, we focus on the 40 X-ray sources in and around pillars 14 at the heart of the Eagle Nebula. None of the X-ray sources are associated with the evaporating gaseous globules (EGGs) first observed by Hester and coworkers) in HST WFPC2 images of M16, implying either that the EGGs do not contain protostars or that the protostars have not yet become X-ray active. Eight X-ray counts are coincident with the Herbig-Haro object HH 216, implying logLX~30.0.
2703. Chandra X-ray observations of M81
ID:
ivo://CDS.VizieR/J/ApJS/144/213
Title:
Chandra X-ray observations of M81
Short Name:
J/ApJS/144/213
Date:
21 Oct 2021
Publisher:
CDS
Description:
A Chandra X-Ray Observatory ACIS-S imaging observation is used to study the population of X-ray sources in the nearby Sab galaxy M81 (NGC 3031). A total of 177 sources are detected with 124 located within the D_25_ isophote to a limiting X-ray luminosity of ~3x10^36^erg/s. Source positions, count rates, luminosities in the 0.3-8.0 keV band, limiting optical magnitudes, and potential counterpart identifications are tabulated. Spectral and timing analysis of the 36 brightest sources are reported including the low-luminosity active galactic nucleus, SN 1993J, and the Einstein-discovered ultraluminous X-ray source X6.
2704. Chandra X-ray observations of M71
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.
2705. Chandra X-ray observations of NGC 2516
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.
2706. Chandra X-ray observations of NGC 1316
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).
2707. Chandra X-ray observations of NGC 2024
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.
2708. Chandra X-ray observations of SDSS-DR5 QSOs
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.
2709. Chandra X-ray Observatory Data Archive
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.
2710. Chandra X-ray point sources in Abell 133
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.

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