- ID:
- ivo://CDS.VizieR/J/A+A/443/103
- Title:
- X-ray properties of NGC 300. I.
- Short Name:
- J/A+A/443/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray properties of NGC 300 point sources, extracted from 66ks of XMM-Newton data taken in 2000 December and 2001 January. A total of 163 sources were detected in the energy range of 0.3-6kev. We report on the global properties of the sources detected inside the D_25_ optical disk, such as the hardness ratio and X-ray fluxes, and on the properties of their optical counterparts found in B, V, and R images from the 2.2m MPG/ESO telescope. Furthermore, we cross-correlate the X-ray sources with SIMBAD, the USNO-A2.0 catalog, and radio catalogues.
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- ID:
- ivo://CDS.VizieR/J/ApJS/194/7
- Title:
- X-ray properties of O and B stars in Carina
- Short Name:
- J/ApJS/194/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the L_X-L_BOL ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(L_X/L_BOL) is 7.26 for single objects, with a dispersion of only 0.21dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the L_X-L_BOL ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the L_X-L_BOL ratio in the medium (1.0-2.5keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared with "normal" O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest among these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes.
- ID:
- ivo://CDS.VizieR/J/MNRAS/422/494
- Title:
- X-ray properties of optically selected ETGs
- Short Name:
- J/MNRAS/422/494
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the X-ray properties of 393 optically selected early-type galaxies (ETGs) over the redshift range of z~~0.0-1.2 in the Chandra Deep Fields (CDFs). To measure the average X-ray properties of the ETG population, we use X-ray stacking analyses with a subset of 158 passive ETGs (148 of which were individually undetected in X-ray). This ETG subset was constructed to span the redshift ranges of z=0.1-1.2 in the ~~4Ms CDF-South and ~~2Ms CDF-North and z=0.1-0.6 in the ~~250ks Extended-CDF-South where the contribution from individually undetected active galactic nuclei (AGN) is expected to be negligible in our stacking.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/122
- Title:
- X-ray properties of PHL1811 analogs and WLQs
- Short Name:
- J/ApJ/805/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an X-ray and multiwavelength study of 33 weak emission-line quasars (WLQs) and 18 quasars that are analogs of the extreme WLQ, PHL1811, at z~0.5-2.9. New Chandra 1.5-9.5ks exploratory observations were obtained for 32 objects while the others have archival X-ray observations. Significant fractions of these luminous type 1 quasars are distinctly X-ray weak compared to typical quasars, including 16 (48%) of the WLQs and 17 (94%) of the PHL 1811 analogs with average X-ray weakness factors of 17 and 39, respectively. We measure a relatively hard ({Gamma}=1.16^+0.37^_-0.32_) effective power-law photon index for a stack of the X-ray weak subsample, suggesting X-ray absorption, and spectral analysis of one PHL 1811 analog, J1521+5202, also indicates significant intrinsic X-ray absorption. We compare composite Sloan Digital Sky Survey spectra for the X-ray weak and X-ray normal populations and find several optical-UV tracers of X-ray weakness, e.g., FeII rest-frame equivalent width (REW) and relative color. We describe how orientation effects under our previously proposed "shielding-gas" scenario can likely unify the X-ray weak and X-ray normal populations. We suggest that the shielding gas may naturally be understood as a geometrically thick inner accretion disk that shields the broad line region from the ionizing continuum. If WLQs and PHL 1811 analogs have very high Eddington ratios, the inner disk could be significantly puffed up (e.g., a slim disk). Shielding of the broad emission-line region by a geometrically thick disk may have a significant role in setting the broad distributions of CIV REW and blueshift for quasars more generally.
- ID:
- ivo://CDS.VizieR/J/ApJ/677/401
- Title:
- Xray properties of protostars in ONC
- Short Name:
- J/ApJ/677/401
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The origin and evolution of the X-ray emission in very young stellar objects (YSOs) are not yet well understood because it is very hard to observe YSOs in the protostellar phase. Using COUP data, we study the X-ray properties of stars in the ONC in different evolutionary classes: luminosities, hydrogen column densities N_H_, effective plasma temperatures, and time variability are compared to understand if the interaction between the circumstellar material and the central object can influence the X-ray emission. We have assembled the deepest and most complete photometric catalog of objects in the ONC region from the UV to 8um using data from the HST Treasury Program; deep and almost simultaneous UBVI and JHK images taken, respectively, with WFI at ESO 2.2m and ISPI at CTIO 4m telescopes; and Spitzer IRAC imaging. We select high-probability candidate Class 0-I protostars, a sample of "bona fide" Class II stars, and a set of Class III stars with IR emission consistent with normal photospheres. Our principal result is that Class 0-Ia objects are significantly less luminous in X-rays, in both the total and hard bands, than the more evolved Class II stars with mass larger than 0.5M_{sun}_; the latter show X-ray luminosities similar to those of Class 0-Ib stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/713/L11
- Title:
- X-ray properties of Seyfert 1 galaxies
- Short Name:
- J/ApJ/713/L11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use publicly available XMM-Newton data to systematically compare the hard X-ray photon indices, {Gamma}_2-10keV_, and the iron K{alpha} emission lines of narrow- and broad-line Seyfert 1 (NLS1 and BLS1) galaxies. We compile a flux-limited (f_2-10keV_>=1x10^-12^erg/s/cm^2^) sample including 114 radio-quiet objects, with the 2-10keV luminosity ranging from 10^41^ to 10^45^erg/s. 86 out of these 114 AGNs are included in the CAIXA catalogue (Bianchi et al. 2009, Cat. J/A+A/495/421). The redshift range of the present sample is z<0.37, with only seven objects having z>0.2.
- ID:
- ivo://CDS.VizieR/J/A+A/475/959
- Title:
- X-ray properties of young stellar objects
- Short Name:
- J/A+A/475/959
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To study the X-ray properties of young stellar objects (YSOs), we analyze an exceptionally sensitive Chandra dataset of the Coronet cluster in the CrA star-forming region, achieving a limiting luminosity of L_X,min_~5x10^26^erg/s for lightly absorbed sources. This dataset represents one of the most sensitive X-ray observations ever obtained of a star-forming region. The X-ray data are used to investigate the membership status of tentative members of the region, to derive plasma temperatures and X-ray luminosities of the YSOs, and to investigate variability on the timescale of several years. 46 of the 92 X-ray sources in the merged Chandra image can be identified with optical or near/mid-infrared counterparts. X-ray emission is detected from all of the previously known optically visible late-type (spectral types G to M) stellar cluster members, from five of the eight brown dwarf candidates, and from nine embedded objects ("protostars") with class 0, class I, or flat-spectrum spectral-energy distributions (SEDs) in the field of view. While the Herbig Ae/Be stars TY CrA and R CrA, a close companion of the B9e star HD 176386, and the F0e star T CrA are detected, no X-ray emission is found from any of the Herbig-Haro (HH) objects or the protostellar cores without infrared source. We find indications for diffuse X-ray emission near R CrA/IRS 7.
- ID:
- ivo://CDS.VizieR/J/A+A/434/385
- Title:
- X-ray/radio data of high energy peaked BL Lacs
- Short Name:
- J/A+A/434/385
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The fully identified complete sample including 150 extreme HBL BL Lacs is presented in Table 1 where we give the source name built with the catalog identification code SHBL (where S stands for "Sedentary" survey and HBL for High energy peaked BL Lacs) and the arcsecond precision optical coordinates of the source taken from the APM and COSMOS on-line services; we give also the RASS name, the X-ray flux (0.1-2.4keV), the radio flux (20cm, from the NVSS survey), and the optical apparent V magnitude (from APM and COSMOS) respectively; we give the redshift when available and the reference for the optical identification. In Table 2 we report properties for five bright elliptical galaxies/low luminosity HBLs in the original sample of high fX/fr sources of Paper I (Giommi et al., 1999MNRAS.310..465G). In Table 3 the 19 rejected emission line AGNs together with their properties are presented.
- ID:
- ivo://CDS.VizieR/J/ApJ/779/133
- Title:
- X-ray & radio fluxes of unassociated 2FGL sources
- Short Name:
- J/ApJ/779/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Fermi Gamma-Ray Space Telescope has been detecting a wealth of sources where the multiwavelength counterpart is either inconclusive or missing altogether. We present a combination of factors that can be used to identify multiwavelength counterparts to these Fermi unassociated sources. This approach was used to select and investigate seven bright, high-latitude unassociated sources with radio, UV, X-ray, and {gamma}-ray observations. As a result, four of these sources are candidates to be active galactic nuclei, and one to be a pulsar, while two do not fit easily into these known categories of sources. The latter pair of extraordinary sources might reveal a new category subclass or a new type of {gamma}-ray emitter. These results altogether demonstrate the power of a multiwavelength approach to illuminate the nature of unassociated Fermi sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/396/2011
- Title:
- X-ray+Radio sources in XBootes
- Short Name:
- J/MNRAS/396/2011
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the goal of investigating the nature and the environment of the faint radio sources (at mJy level), here are presented results of X-ray identifications of Faint Imaging Radio Survey at Twenty centimetres (FIRST) in the 9deg^2^ Bootes field of the National Optical Astronomy Observatory (NOAO) Deep Wide Field Survey (NDWFS), using data from the Chandra XBootes survey. A total of 92 (10 per cent) FIRST radio sources are identified above the X-ray flux limit f_X_)(0.5-7)keV=8x10^-15^erg/s/cm^2^, and 79 optical counterparts are common to both the radio and X-ray sources. Spectroscopic identifications [obtained from the Sloan Digital Sky Survey (SDSS) survey] were available for 22 sources (27 per cent).
