- ID:
- ivo://CDS.VizieR/J/MNRAS/323/757
- Title:
- Deep X-Ray Radio Blazar Survey (DXRBS). II.
- Short Name:
- J/MNRAS/323/757
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have searched the archived, pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the WGACAT X-ray data base with several publicly available radio catalogues, restricting our candidate list to serendipitous X-ray sources with a flat radio spectrum ({alpha}_r_<=0.70, where S_{nu}_~{nu}^-{alpha}^). his makes up the Deep X-ray Radio Blazar Survey (DXRBS). Here we present new identifications and spectra for 106 sources, including 86 radio-loud quasars, 11 BL Lacertae objects, and nine narrow-line radio galaxies. Together with our previously published objects and already-known sources, our sample now contains 298 identified objects: 234 radio-loud quasars [181 flat-spectrum quasars: FSRQ ({alpha}_r_<=0.50) and 53 steep-spectrum quasars: SSRQ], 36 BL Lacs and 28 narrow-line radio galaxies. Redshift information is available for 96 per cent of these. Thus our selection technique is ~90 per cent efficient at finding radio-loud quasars and BL Lacs. Reaching 5-GHz radio fluxes ~50mJy and 0.1-2.0keV X-ray fluxes a few W10-14erg/cm^2^/s, DXRBS is the faintest and largest flat-spectrum radio sample with nearly complete (~85 per cent) identification.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/817/103
- Title:
- Definitive Swift/XRT LC of Swift J164449.3+573451
- Short Name:
- J/ApJ/817/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On 2011 March 28, the Swift Burst Alert Telescope triggered on an object that had no analog in over six years of Swift operations. Follow-up observations by the Swift X-ray Telescope (XRT) found a new, bright X-ray source covering three orders of magnitude in flux over the first few days, that was much more persistent (and variable) than gamma-ray burst afterglows. Ground-based spectroscopy found a redshift of 0.35, implying extremely high luminosity, with integrated isotropic-equivalent energy output in the X-ray band alone exceeding 10^53^erg in the first two weeks after discovery. Strong evidence for a collimated outflow or beamed emission was found. The observational properties of this object are unlike anything ever before observed. We interpret these unique properties as the result of emission from a relativistic jet produced in the aftermath of the tidal disruption of a main sequence star by a massive black hole (BH) in the center of the host galaxy. The source decayed slowly as the stellar remnants were accreted onto the BH, before abruptly shutting off. Here we present the definitive XRT team light curve for Swift J164449.3+573451 and discuss its implications. We show that the unabsorbed flux decayed roughly as a t^-1.5^ power law up to 2012 August 17. The steep turnoff of an order of magnitude in 24 hr seems to be consistent with the shutdown of the jet as the accretion disk transitioned from a thick disk to a thin disk. Swift continues to monitor this source in case the jet reactivates.
- ID:
- ivo://CDS.VizieR/J/ApJS/202/14
- Title:
- Diffuse OVII and OVIII emission from XMM
- Short Name:
- J/ApJS/202/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an all-sky catalog of diffuse OVII and OVIII line intensities, extracted from archival XMM-Newton observations. This catalog supersedes our previous catalog (Henley et al., 2010, Cat. J/ApJS/187/388), which covered the sky between l=120{deg} and l=240{deg}. We attempted to reduce the contamination from near-Earth solar wind charge exchange (SWCX) emission by excluding times of high solar wind proton flux from the data. Without this filtering, we were able to extract measurements from 1868 observations. With this filtering, nearly half of the observations became unusable, and only 1003 observations yielded measurements. The OVII and OVIII intensities are typically ~2-11 and <~3 photons/cm^2^/s/sr (line unit, L.U.), respectively, although much brighter intensities were also recorded. Our data set includes 217 directions that have been observed multiple times by XMM-Newton. The time variation of the intensities from such directions may be used to constrain SWCX models.
- ID:
- ivo://CDS.VizieR/J/AJ/155/81
- Title:
- Diffuse X-ray-emitting gas in major mergers
- Short Name:
- J/AJ/155/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using archived data from the Chandra X-ray telescope, we have extracted the diffuse X-ray emission from 49 equal-mass interacting/merging galaxy pairs in a merger sequence, from widely separated pairs to merger remnants. After the removal of contributions from unresolved point sources, we compared the diffuse thermal X-ray luminosity from hot gas (L_X_(gas)) with the global star formation rate (SFR). After correction for absorption within the target galaxy, we do not see a strong trend of L_X_(gas)/SFR with the SFR or merger stage for galaxies with SFR>1 M_{sun}_/yr. For these galaxies, the median L_X_(gas)/SFR is 5.5x10^39^ ((erg/s)/M_{sun}_/yr), similar to that of normal spiral galaxies. These results suggest that stellar feedback in star-forming galaxies reaches an approximately steady-state condition, in which a relatively constant fraction of about 2% of the total energy output from supernovae and stellar winds is converted into X-ray flux. Three late-stage merger remnants with low SFRs and high K-band luminosities (L_K_) have enhanced L_X_(gas)/SFR; their UV/IR/optical colors suggest that they are post-starburst galaxies, perhaps in the process of becoming ellipticals. Systems with L_K_<10^10^ L_{sun}_ have lower L_X_(gas)/SFR ratios than the other galaxies in our sample, perhaps due to lower gravitational fields or lower metallicities. We see no relation between L_X_(gas)/SFR and Seyfert activity in this sample, suggesting that feedback from active galactic nuclei is not a major contributor to the hot gas in our sample galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/569/689
- Title:
- Distant cluster hunting. II.
- Short Name:
- J/ApJ/569/689
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and analyze the optical and X-ray catalogs of moderate-redshift cluster candidates from the ROSAT Optical X-Ray Survey, or ROXS. The survey covers the sky area contained in the fields of view of 23 deep archival ROSAT PSPC pointings, 4.8 square degrees. The cross-correlated cluster catalogs were constructed by comparing two independent catalogs extracted from the optical and X-ray bandpasses, using a matched-filter technique for the optical data and a wavelet technique for the X-ray data. We cross-identified cluster candidates in each catalog.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A56
- Title:
- Distant clusters of galaxies in the 2XMM/SDSS
- Short Name:
- J/A+A/607/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galaxy clusters at high redshift are important to test cosmological models and models for the growth of structure. They are difficult to find in wide-angle optical surveys, however, leaving dedicated follow-up of X-ray selected candidates as one promising identification route. We aim to increase the number of galaxy clusters beyond the SDSS-limit, z~0.75. We compiled a list of extended X-ray sources from the 2XMMp catalogue within the footprint of the Sloan Digital Sky Survey. Fields without optical counterpart were selected for further investigation. Deep optical imaging and follow-up spectroscopy were obtained with the Large Binocular Telescope, Arizona (LBT), of those candidates not known to the literature. From initially 19 candidates, selected by visually screening X-ray images of 478 XMM-Newton observations and the corresponding SDSS images, 6 clusters were found in the literature. Imaging data through r,z filters were obtained for the remaining candidates, and 7 were chosen for multi-object (MOS) spectroscopy. Spectroscopic redshifts, optical magnitudes, and X-ray parameters (flux, temperature, and luminosity) are presented for the clusters with spectroscopic redshifts. The distant clusters studied here constitute one additional redshift bin for studies of the L-T relation, which does not seem to evolve from high to low redshifts. The selection method of distant galaxy clusters presented here was highly successful. It is based solely on archival optical (SDSS) and X-ray (XMM-Newton) data. Out of 19 selected candidates, 6 of the 7 candidates selected for spectroscopic follow-up were verified as distant clusters, a further candidate is most likely a group of galaxies at z~1.21. Out of the remaining 12 candidates, 6 were known previously as galaxy clusters, one object is a likely X-ray emission from an AGN radio jet, and for 5 we see no clear evidence for them to be high-redshift galaxy clusters.
- ID:
- ivo://CDS.VizieR/J/MNRAS/392/1509
- Title:
- Distribution of AGNs in galaxy clusters
- Short Name:
- J/MNRAS/392/1509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the X-ray point source populations in 182 Chandra images of galaxy clusters at z>0.1 with exposure time >10ks, as well as 44 non-cluster fields. The analysis of the number and flux of these sources, using a detailed pipeline to predict the distribution of non-cluster sources in each field, reveals an excess of X-ray point sources associated with the galaxy clusters. A sample of 148 galaxy clusters at 0.1<z<0.9 , with no other nearby clusters, shows an excess of 230 cluster sources in total, an average of ~1.5 sources per cluster. The lack of optical data for these clusters limits the physical interpretation of this result, as we cannot calculate the fraction of cluster galaxies hosting X-ray sources. However, the fluxes of the excess sources indicate that over half of them are very likely to be active galactic nuclei (AGN), and the radial distribution shows that they are quite evenly distributed over the central 1Mpc of the cluster, with almost no sources found beyond this radius. We also use this pipeline to successfully reproduce the results of previous studies, particularly the higher density of sources in the central 0.5Mpc of a few cluster fields, but show that these conclusions are not generally valid for this larger sample of clusters. We conclude that some of these differences may be due to the sample properties, such as the size and redshift of the clusters studied, or a lack of publications for cluster fields with no excess sources. This paper also presents the basic X-ray properties of the galaxy clusters, and in subsequent papers in this series the dependence of the AGN population on these cluster properties will be evaluated.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A157
- Title:
- Dolidze 25 Chandra/ACIS-I X-ray sources
- Short Name:
- J/A+A/650/A157
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The dispersal of protoplanetary disks sets the timescale available for planets to assemble, and thus it is one of the fundamental parameters in theories of planetary formation. Disk dispersal is determined by several properties of the central star, the disk itself, and the surrounding environment. In particular, the metallicity of disks may impact their evolution, even if to date controversial results exist: in low-metallicity clusters disks seem to rapidly disperse, while in the Magellanic Clouds some evidence supports the existence of accreting disks few tens of Myrs old. In this paper we study the dispersal timescale of disks in Dolidze 25, the young cluster in proximity of the Sun with lowest metallicity, with the aim of understanding whether disk evolution is impacted by the low-metallicity of the cluster. We have analyzed Chandra/ACIS-I observations of the cluster and combined the resulting source catalog with existing optical and infrared catalogs of the region. We selected the disk-bearing population in a 1 degree circular region centered on Dolidze~25 from criteria based on infrared colors, and the disk-less population within a smaller central region among the X-ray sources with OIR counterpart. In both cases, criteria are applied to discard contaminating sources in the foreground/background. We have derived stellar parameters from isochrones fitted to color-magnitude diagrams. We derived a disk fraction of about 34% and a median age of the cluster of 1.2Myrs. To minimize the impact of incompleteness and spatial inhomogeneity of the list of members, we restricted this calculation to stars in a magnitude range where our selection of cluster members is fairly complete and by adopting different cuts in stellar masses. By comparing this estimate with existing estimates of the disk fraction of clusters younger than 10Myrs, our study suggests that the disk fraction of Dolidze 25 is lower than what is expected from its age alone. Even if our results are not conclusive given the intrinsic uncertainty on stellar ages estimated from isochrones fitting to color-magnitude diagrams, we suggest that disk evolution in Dolidze 25 may be impacted by the environment. Given the poor O star population and low stellar density of the cluster, it is more likely that disks dispersal timescale is dictated more by the low metallicity of the cluster rather than external photoevaporation or dynamical encounters.
- ID:
- ivo://CDS.VizieR/J/other/RAA/14.1135
- Title:
- Doppler factor for a Fermi blazar sample
- Short Name:
- J/other/RAA/14.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We selected 457 blazars (193 flat spectrum radio quasars, 61 low-synchrotron peaked blazars, 69 intermediate-synchrotron peaked blazars and 134 high-synchrotron peaked blazars) from the second Fermi-LAT catalog (2FGL) of {gamma}-ray sources, which have X-ray observations. We calculated the lower limits for their Doppler factors, {delta}_{gamma}_, and compared the lower limits with the available Doppler factors and the apparent superluminal velocities in the literature.
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/1561
- Title:
- DR 21 Chandra source catalogue
- Short Name:
- J/MNRAS/437/1561
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have studied the young low-mass pre-main sequence (PMS) stellar population associated with the massive star-forming region DR 21 by using archival X-ray Chandra observations and by complementing them with existing optical and infrared (IR) surveys. The Chandra observations have revealed for the first time a new highly extincted population of PMS low-mass stars previously missed in observations at other wavelengths. The X-ray population exhibits three main stellar density peaks, coincident with the massive star-forming regions, being the DR 21 core the main peak. The cross-correlated X-ray/IR sample exhibits a radial 'Spokes-like' stellar filamentary structure that extends from the DR 21 core towards the northeast. The near-IR data reveal a centrally peaked structure for the extinction, which exhibits its maximum in the DR 21 core and gradually decreases with the distance to the N-S cloud axis and to the cluster centre. We find evidence of a global mass segregation in the full low-mass stellar cluster, and of a stellar age segregation, with the youngest stars still embedded in the N-S cloud, and more evolved stars more spatially distributed. The results are consistent with the scenario where an elongated overall potential well created by the full low-mass stellar cluster funnels gas through filaments feeding stellar formation. Besides the full gravitational well, smaller scale local potential wells created by dense stellar sub-clusters of low-mass stars are privileged in the competition for the gas of the common reservoir, allowing the formation of massive stars. We also discuss the possibility that a stellar collision in the very dense stellar cluster revealed by Chandra in the DR 21 core is the origin of the large-scale and highly energetic outflow arising from this region.