- ID:
- ivo://CDS.VizieR/J/MNRAS/274/1194
- Title:
- Optical Identifications of ROSAT EUV Sources
- Short Name:
- J/MNRAS/274/1194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Optical identifications for 195 EUV sources located in the ROSAT Wide Field Camera all-Sky survey are presented. We list 69 previous unknown EUV-emitting white dwarfs, 114 active stars, 7 new magnetic cataclysmic variables and 5 active galaxies. Several of the white dwarfs have resolved M-type companions, while five are unresolved white dwarf/M-star pairs. Finding charts are given for the optical counterparts.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/127/2579
- Title:
- Optical ident. of BATC Sky Survey X-ray sources
- Short Name:
- J/AJ/127/2579
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical candidates for 75 X-ray sources in a 1deg^2^ overlapping region with the 1997 medium-deep ROSAT survey by Molthagen et al. (1996, Cat. <J/A+AS/126/509>). These candidates are selected using the multicolor CCD imaging observations made for the T329 field of the Beijing-Arizona-Taiwan-Connecticut (BATC) Sky Survey, which uses the NAOC 0.6/0.9m Schmidt telescope with 15 intermediate-band filters covering the wavelength range 3360-9745{AA}. These X-ray sources are relatively faint (CR<<0.2ct/s) and thus are mostly not included in the ROSAT Bright Source Catalogue; they also remain as X-ray sources without optical candidates in a previous identification program carried out by the Hamburg Quasar Survey (1998, <J/A+AS/128/507> and 1999, <J/A+AS/134/483>).
- ID:
- ivo://CDS.VizieR/J/A+A/414/487
- Title:
- Optically bright AGN in ROSAT-FSC
- Short Name:
- J/A+A/414/487
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To build a large, optically bright, X-ray selected AGN sample we have correlated the ROSAT-FSC (<IX/29>) catalogue of X-ray sources with the USNO (<I/252>) catalogue limited to objects brighter than O=16.5 and then with the APS (<VII/214>) database. Each of the 3212 coincidences was classified using the slitless Hamburg spectra. 493 objects were found to be extended and 2719 starlike. Using both the extended objects and the galaxies known from published catalogues we built up a sample of 185 galaxies with O(APS)<17.0mag, which are high-probability counterparts of RASS-FSC X-ray sources. 130 galaxies have a redshift from the literature and for another 34 we obtained new spectra. The fraction of Seyfert galaxies in this sample is 20%. To select a corresponding sample of 144 high-probability counterparts among the starlike sources we searched for very blue objects in an APS-based color-magnitude diagram. Forty-one were already known AGN and for another 91 objects we obtained new spectra, yielding 42 new AGN, increasing their number in the sample to 83. This confirms that surveys of bright QSOs are still significantly incomplete. On the other hand we find that, at a flux limit of 0.02ct/s and at this magnitude, only 40% of all QSOs are detected by ROSAT.
- ID:
- ivo://CDS.VizieR/J/A+A/424/545
- Title:
- Optically faint obscured quasars
- Short Name:
- J/A+A/424/545
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Virtual Observatory (VO) tools to identify optically faint, obscured (i.e., type 2) active galactic nuclei (AGN) in the two Great Observatories Origins Deep Survey (GOODS) fields. By employing publicly available X-ray and optical data and catalogues we discover 68 type 2 AGN candidates.
- ID:
- ivo://CDS.VizieR/J/ApJ/678/1127
- Title:
- Optical photometry of GRB 070610
- Short Name:
- J/ApJ/678/1127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- GRB 070610 is a typical high-energy event with a duration of 5s. Yet within the burst localization we detect a highly unusual X-ray and optical transient, Swift J195509.6+261406. We see high-amplitude X-ray and optical variability on very short timescales even at late times. Using near-infrared imaging assisted by a laser guide star and adaptive optics, we identified the counterpart of Swift J195509.6+261406. Late-time optical and near-infrared imaging constrain the spectral type of the counterpart to be fainter than a K-dwarf, assuming it is of Galactic origin. It is possible that GRB 070610 and Swift J195509.6+261406 are unrelated sources. However, the absence of a typical X-ray afterglow from GRB 070610 in conjunction with the spatial and temporal coincidence of the two motivate us to suggest that the sources are related. The closest (imperfect) analog to Swift J195509.6+261406 is V4641 Sgr, an unusual black hole binary. We suggest that Swift J195509.6+261406 along with V4641 Sgr define a subclass of stellar black hole binaries-the fast X-ray novae. We further suggest that fast X-ray novae are associated with bursts of gamma rays. If so, GRB 070610 defines a new class of celestial gamma-ray bursts and these bursts dominate the long-duration GRB demographics.
- ID:
- ivo://CDS.VizieR/J/AJ/128/1483
- Title:
- Optical properties of the CLASXS X-ray sample
- Short Name:
- J/AJ/128/1483
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present photometric and spectroscopic observations of the X-ray sources detected in the wide-area, moderately deep Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest field. We have B, V, R, I, and z' photometry for 521 (99%) of the 525 sources in the X-ray catalog and spectroscopic redshifts for 271 (52%), including 20 stars. We do not find evidence for redshift groupings of the X-ray sources, like those found in the Chandra Deep Field surveys, because of the larger solid angle covered by this survey. We separate the X-ray sources by optical spectral type and examine the colors, apparent and absolute magnitudes, and redshift distributions for the broad-line and nonbroad-line active galactic nuclei. Combining our wide-area survey with other Chandra and XMM-Newton hard X-ray surveys, we find a definite lack of luminous, high accretion rate sources at z<1, consistent with previous observations that showed that supermassive black hole growth is dominated at low redshifts by sources with low accretion rates.
- ID:
- ivo://CDS.VizieR/J/ApJ/895/114
- Title:
- Optical, radio and X-ray properties for 113 QSOs
- Short Name:
- J/ApJ/895/114
- Date:
- 16 Mar 2022 00:19:12
- Publisher:
- CDS
- Description:
- We investigate whether the correlation between the hard X-ray photon index ({Gamma}) and accretion rate for super-Eddington accreting quasars is different from that for sub-Eddington accreting quasars. We construct a sample of 113 bright quasars from the Sloan Digital Sky Survey Data Release 14 quasar catalog, with 38 quasars as the super-Eddington subsample and 75 quasars as the sub-Eddington subsample. We derive black hole masses using a simple-epoch virial mass formula based on the H{beta} lines, and we use the standard thin disk model to derive the dimensionless accretion rates (M) for our sample. The X-ray data for these quasars are collected from the Chandra and XMM-Newton archives. We fit the hard X-ray spectra using a single power-law model to obtain {Gamma} values. We find a statistically significant (R_S_=0.43, p=7.75x10^-3^) correlation between {Gamma} and M for the super-Eddington subsample. The {Gamma}-M correlation for the sub-Eddington subsample is also significant, but weaker (R_S_=0.30, p=9.98x10^-3^). Linear regression analysis shows that {Gamma}=(0.34{+/-}0.11)log(M)+(1.71{+/-}0.17) and {Gamma}=(0.09{+/-}0.04)log(M)+(1.93{+/-}0.04) for the super- and sub-Eddington subsamples, respectively. The {Gamma}-M correlations of the two subsamples are different, suggesting different disk-corona connections in these two types of systems. We propose one qualitative explanation of the steeper {Gamma}-M correlation in the super-Eddington regime that involves larger seed photon fluxes received by the compact coronae from the thick disks in super-Eddington accreting quasars.
- ID:
- ivo://CDS.VizieR/J/ApJS/191/124
- Title:
- Optical spectroscopy of ECDF-S X-ray sources
- Short Name:
- J/ApJS/191/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a program to acquire high-quality optical spectra of X-ray sources detected in the Extended-Chandra Deep Field-South (E-CDF-S) and its central 2Ms area. New spectroscopic redshifts, up to z=4, are measured for 283 counterparts to Chandra sources with deep exposures (t~2-9hr per pointing) using multi-slit facilities on both VLT (VIMOS) and Keck (DEIMOS), thus bringing the total number of spectroscopically identified X-ray sources to over 500 in this survey field. Since our new spectroscopic identifications are mainly associated with X-ray sources in the shallower 250ks coverage, we provide a comprehensive catalog of X-ray sources detected in the E-CDF-S including the optical and near-infrared counterparts, determined by a likelihood routine, and redshifts (both spectroscopic and photometric), that incorporate published spectroscopic catalogs, thus resulting in a final sample with a high fraction (80%) of X-ray sources having secure identifications. Our redshift catalog includes 17 type-2 QSOs at 1<~z<~3.5. Based on our deepest (9 hr) VLT/VIMOS observation, we identify "elusive" optically faint galaxies (Rmag~25) at z~2-3 based upon the detection of interstellar absorption lines (e.g., OII+SiIV, CII], CIV).
- ID:
- ivo://CDS.VizieR/J/ApJ/833/149
- Title:
- Opt/NIR obs. of M31N 2008-12a 2015 eruption
- Short Name:
- J/ApJ/833/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption 10 times, including yearly eruptions from 2008 to 2014. With a measured recurrence period of P_rec_=351+/-13days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground- and space-based follow-up programs. In this paper we present the 2015 detection, visible to near-infrared photometry and visible spectroscopy, and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2m (Hawaii) discovered the 2015 eruption, estimated to have commenced at August 28.28+/-0.12UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities ~13000km/s, possibly collimated outflows. Photometric and spectroscopic observations of the eruption provide strong evidence supporting a red giant donor. An apparently stochastic variability during the early supersoft X-ray phase was comparable in amplitude and duration to past eruptions, but the 2013 and 2015 eruptions show evidence of a brief flux dip during this phase. The multi-eruption Swift/XRT spectra show tentative evidence of high-ionization emission lines above a high-temperature continuum. Following Henze+ (2015A&A...582L...8H), the updated recurrence period based on all known eruptions is P_rec_=174+/-10days, and we expect the next eruption of M31N 2008-12a to occur around 2016 mid-September.
- ID:
- ivo://CDS.VizieR/J/AJ/152/11
- Title:
- Orbits of four triple stars
- Short Name:
- J/AJ/152/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Each of the nearby triple systems HIP 7601, 13498, 23824, and 113597 (HD 10800, 18198, 35877, 217379) consist of solar-type dwarfs with comparable masses, where all three components are resolved spectrally, while the outer pairs are resolved both visually and spectrally. These stars are relatively young (between 100 and 600Myr) and chromospherically active (X-ray sources), although they rotate slowly. I determine the spectroscopic orbits of the inner subsystems (periods 19.4, 14.1, 5.6, 20.3days) and the orbits of the outer systems (periods 1.75, 51, 27, 500years, respectively). For HIP 7601 and 13498, the combined spectro-interferometric outer orbits produce direct measurement of the masses of all of the components, allowing for a comparison with stellar models. The 6708{AA} lithium line is present and its strength is measured in each component individually by subtracting the contributions of the other components. The inner and outer orbits of HIP 7601 are nearly circular, likely co-planar, and have a modest period ratio of 1:33. This study contributes to the characterization of hierarchical multiplicity in the solar neighborhood and provides data for testing stellar evolutionary models and chronology.