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17841. X-rays from the star-forming complex W40
ID:
ivo://CDS.VizieR/J/ApJ/725/2485
Title:
X-rays from the star-forming complex W40
Short Name:
J/ApJ/725/2485
Date:
21 Oct 2021
Publisher:
CDS
Description:
The young stellar cluster illuminating the W40 HII region, one of the nearest massive star-forming regions, has been observed with the ACIS detector on board the Chandra X-ray Observatory. Due to its high obscuration, this is a poorly studied stellar cluster with only a handful of bright stars visible in the optical band, including three OB stars identified as primary excitation sources. We detect 225 X-ray sources, of which 85% are confidently identified as young stellar members of the region. Two potential distances of the cluster, 260pc and 600pc, are used in the paper.
17842. X-rays in the Orion nebula cluster
ID:
ivo://CDS.VizieR/J/ApJ/584/911
Title:
X-rays in the Orion nebula cluster
Short Name:
J/ApJ/584/911
Date:
21 Oct 2021
Publisher:
CDS
Description:
A recent observation of the Orion Nebula Cluster with the ACIS instrument on board the Chandra X-Ray Observatory detected 1075 sources, 525 of which are pre-main-sequence (PMS) stars with measured bulk properties such as bolometric luminosities, masses, ages, and disk indicators. Nearly half of these stars have photometrically measured rotational periods. This provides a uniquely large and well-defined sample to study the dependence of magnetic activity on bulk properties for stars descending the Hayashi tracks.
17843. X-rays obs. in 8 young open star clusters
ID:
ivo://CDS.VizieR/J/other/JApA/34.393
Title:
X-rays obs. in 8 young open star clusters
Short Name:
J/other/JApA/34.
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a detailed investigation of X-ray source contents of eight young open clusters with ages between 4 to 46Myr using archival X-ray data from XMM-Newton. The probable cluster memberships of the X-ray sources have been established on the basis of multi-wavelength archival data, and samples of 152 pre-main sequence (PMS) low mass (<2M_{sun}_), 36 intermediate mass (2-10M_{sun}_) and 16 massive (>10M_{sun}_) stars have been generated. X-ray spectral analyses of high mass stars reveal the presence of high temperature plasma with temperature <2keV, and mean L_X_/L_bol_ of 10^-6.9^. In the case of PMS low mass stars, the plasma temperatures have been found to be in the range of 0.2keV to 3keV with a median value of ~1.3keV, with no significant difference in plasma temperatures during their evolution from 4 to 46Myr. The X-ray luminosity distributions of the PMS low mass stars have been found to be similar in the young star clusters under study. This may suggest a nearly uniform X-ray activity in the PMS low mass stars of ages ~4--14Myr. These observed values of L_X)/L_bol_ are found to have a mean value of 10^-3.6^+/-0.4, which is below the X-ray saturation level. The L_X_/L_bol_ values for the PMS low mass stars are well correlated with their bolometric luminosities, that implies its dependence on the internal structure of the low mass stars. The difference between the X-ray luminosity distributions of the intermediate mass stars and the PMS low mass stars has not been found to be statistically significant. Their L_X_/L_bol_ values, however have been found to be significantly different from each other with a confidence level greater than 99.999% and the strength of X-ray activity in the intermediate mass stars is found to be lower compared to the low mass stars. However, the possibility of X-ray emission from the intermediate mass stars due to a low mass star in close proximity of the intermediate mass star can not be ruled out.
17844. X-Ray source properties for NGC 2207/IC 2163
ID:
ivo://CDS.VizieR/J/ApJ/797/91
Title:
X-Ray source properties for NGC 2207/IC 2163
Short Name:
J/ApJ/797/91
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comprehensive study of the total X-ray emission from the colliding galaxy pair NGC 2207/IC 2163, based on Chandra, Spitzer, and GALEX data. We detect 28 ultraluminous X-ray sources (ULXs), 7 of which were not detected previously because of X-ray variability. Twelve sources show significant long-term variability, with no correlated spectral changes. Seven sources are transient candidates. One ULX coincides with an extremely blue star cluster (B-V=-0.7). We confirm that the global relation between the number and luminosity of ULXs and the integrated star-formation rate (SFR) of the host galaxy also holds on local scales. We investigate the effects of dust extinction and age on the X-ray binary (XRB) population on subgalactic scales. The distributions of N_X_ and L_X_ are peaked at L_IR_/L_NUV_~1, which may be associated with an age of ~10 Myr for the underlying stellar population. We find that approximately one-third of the XRBs are located in close proximity to young star complexes. The luminosity function of the XRBs is consistent with that typical for high-mass XRBs and appears unaffected by variability. We disentangle and compare the X-ray diffuse spectrum with that of the bright XRBs. The hot interstellar medium dominates the diffuse X-ray emission at E<~1 keV and has a temperature kT=0.28_-0.04_^+0.05^ keV and intrinsic 0.5-2 keV luminosity of 7.9x10^40^ erg/s, a factor of ~2.3 higher than the average thermal luminosity produced per unit SFR in local star-forming galaxies. The total X-ray output of NGC 2207/IC 2163 is 1.5x10^41^ erg/s, and the corresponding total integrated SFR is 23.7 M_{sun}_/yr.
17845. X-ray sources around G12.82-0.02
ID:
ivo://CDS.VizieR/J/ApJ/665/1297
Title:
X-ray sources around G12.82-0.02
Short Name:
J/ApJ/665/1297
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a Chandra X-ray observation of G12.82-0.02, a shell-like radio supernova remnant coincident with the TeV gamma-ray source HESS J1813-178. We resolve the X-ray emission from the colocated Advanced Satellite for Cosmology and Astrophysics (ASCA) source into a point source surrounded by structured diffuse emission that fills the interior of the radio shell. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula.
17846. X-ray sources close to 3C 295 galaxy cluster
ID:
ivo://CDS.VizieR/J/A+A/484/303
Title:
X-ray sources close to 3C 295 galaxy cluster
Short Name:
J/A+A/484/303
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a detailed analysis of the overdensity of X-ray sources close to the 3C 295 galaxy cluster (z=0.46) to assess whether it is associated with a filament of the large-scale structure of the Universe. We obtained optical spectra of the optical counterparts of eleven sources associated with the filament, finding that one is at z=0.474. This is a type 1 AGN at 1.5' from the cluster center. We found three more sources with a redshift in the range 0.37/0.53. We extracted the stacked X-ray spectrum of 47 X-ray sources belonging to the putative filament.
17847. X-ray sources <1 degree from Seyfert galaxies
ID:
ivo://CDS.VizieR/J/A+A/319/18
Title:
X-ray sources <1 degree from Seyfert galaxies
Short Name:
J/A+A/319/18
Date:
21 Oct 2021
Publisher:
CDS
Description:
Archived PSPC observations of 26 Seyfert galaxies have been analyzed for bright X-ray sources out to the full extent of the field (< about 50'). Of all Seyferts known this represents a sample 88% complete to B_T_=10mag, 74% complete to 11mag and 50% complete to 12mag. Using the same reduction algorithm, 14 fields centered on stars at high galactic latitudes have been used as control fields. Excluding the two brightest Seyferts, a subset of 24 Seyferts with corrected apparent magnitude between 8.04<B^o,i^_T_<12.90mag show a minimum excess of 46 bright X-ray sources generally distributed between 10 and 25' from the target galaxy. The significances of association of these sources with the Seyferts in the median brightness range are as high as 7.4-sigma.
17848. X-ray sources in A194 and A1060
ID:
ivo://CDS.VizieR/J/PASJ/58/931
Title:
X-ray sources in A194 and A1060
Short Name:
J/PASJ/58/931
Date:
21 Oct 2021
Publisher:
CDS
Description:
Two nearby clusters of galaxies, A194 (z=0.018) and A1060 (z=0.0114), have been analyzed for their X-ray point-source properties with XMM-Newton EPIC-PN data. A multi-band source detection technique was applied to both of the clusters, resulting in 46 sources from the A194 field and 32 sources from the A1060 field, respectively. The cumulative log(N)-log(S) for a flux limit of F_X_>=1x10^-14^erg/cm^2^/s was calculated and compared with that of the Lockman Hole. A ~3{sigma} excess of X-ray sources was found for the cluster regions.
17849. X-ray sources in CMa OB1
ID:
ivo://CDS.VizieR/J/A+A/609/A127
Title:
X-ray sources in CMa OB1
Short Name:
J/A+A/609/A127
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Canis Major OB1 association has an intriguing scenario of star formation, especially in the region called Canis Major R1 (CMa R1) traditionally assigned to a reflection nebula, but in reality an ionized region. This work is focussed on the young stellar population associated with CMa R1, for which our previous results from ROSAT, optical, and near-infrared data had revealed two stellar groups with different ages, suggesting a possible mixing of populations originated from distinct star formation episodes. The X-ray data allow the detected sources to be characterized according to hardness ratios, light curves, and spectra. Estimates of mass and age were obtained from the 2MASS catalogue and used to define a complete subsample of stellar counterparts for statistical purposes. A catalogue of 387 XMM-Newton sources is provided, of which 78% are confirmed as members or probable members of the CMa R1 association. Flares (or similar events) were observed for 13 sources and the spectra of 21 bright sources could be fitted by a thermal plasma model. Mean values of fits parameters were used to estimate X-ray luminosities. We found a minimum value of log(L_X_[erg/s])=29.43, indicating that our sample of low-mass stars (M*<=0.5 M_{sun}_), which are faint X-ray emitters, is incomplete. Among the 250 objects selected as our complete subsample (defining our "best sample"), 171 are found to the east of the cloud, near Z CMa and dense molecular gas, of which 50% of them are young (<5Myr) and 30% are older (>10Myr). The opposite happens to the west, near GU CMa, in areas lacking molecular gas: among 79 objects, 30% are young and 50% are older. These findings confirm that a first episode of distributed star formation occurred in the whole studied region ~10Myr ago and dispersed the molecular gas, while a second, localized episode (<5Myr) took place in the regions where molecular gas is still present.
17850. X-ray sources in Cyg OB2 region
ID:
ivo://CDS.VizieR/J/ApJS/184/84
Title:
X-ray sources in Cyg OB2 region
Short Name:
J/ApJS/184/84
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalogue of 1696 X-ray sources detected in the massive star forming region (SFR) Cygnus OB2 and extracted from two archival Chandra observations of the center of the region. A deep source extraction routine, exploiting the low background rates of Chandra observations was employed to maximize the number of sources extracted. Observations at other wavelengths were used to identify low count-rate sources and remove likely spurious sources. Monte Carlo simulations were also used to assess the authenticity of these sources. X-ray spectra were fitted with thermal plasma models to characterize the objects and X-ray light curves were analyzed to determine their variability. We used a Bayesian technique to identify optical or near-IR counterparts for 1501 (89%) of our sources, using deep observations from the INT Photometric H-alpha Survey, the Two Micron All Sky Survey, and the UKIRT Infrared Deep Sky Survey-Galactic plane Survey. 755 (45%) of these objects have six-band r', H-alpha, i', J, H, and K optical and near-IR photometry. From an analysis of the Poisson false-source probabilities for each source we estimate that our X-ray catalogue includes <1% of false sources, and an even lower fraction when only sources with optical or near-IR associations are considered. A Monte Carlo simulation of the Bayesian matching scheme allows this method to be compared to more simplified matching techniques and enables the various sources of error to be quantified. The catalogue of 1696 objects presented here includes X-ray broad band fluxes, model fits, and optical and near-IR photometry in what is one of the largest X-ray catalogue of a single SFR to date. The high number of stellar X-ray sources detected from relatively shallow observations confirms the status and importance of Cygnus OB2 as one of our Galaxy's most massive SFRs.

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