- ID:
- ivo://CDS.VizieR/J/MNRAS/318/1073
- Title:
- Hard spectrum ROSAT sources. I.
- Short Name:
- J/MNRAS/318/1073
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of 147 serendipitous X-ray sources selected to have hard spectra ({alpha}<0.5) from a survey of 188 ROSAT fields. Such sources must be the dominant contributors to the X-ray background at faint fluxes. We have used Monte Carlo simulations to verify that our technique is very efficient at selecting hard sources: the survey has >=10 times as much effective area for hard sources as it has for soft sources above a 0.5-2keV flux level of 10^-14^erg/cm^2^/s. The distribution of best-fitting spectral slopes of the hard sources suggests that a typical ROSAT hard source in our survey has a spectral slope {alpha}~0. The hard sources have a steep number flux relation (dN/dS_{mu}_S^-{gamma}^ with a best-fitting value of {gamma}=2.72+/-0.12) and make up about 15 per cent of all 0.5-2keV sources with S>10^-14^erg/cm^2^/s. If their N(S) continues to fainter fluxes, the hard sources will comprise ~40 per cent of sources with 5x10^-15^<S<10^-14^erg/cm^2^/s. The population of hard sources can therefore account for the harder average spectra of ROSAT sources with S<10^-14^erg/cm^2^/s. They probably make a strong contribution to the X-ray background at faint fluxes and could be the solution to the X-ray background spectral paradox.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/PAZh/37/651
- Title:
- Hard X-ray bursts by INTEGRAL in 2003-2009
- Short Name:
- J/PAZh/37/651
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To find X-ray bursts from sources within the field of view of the IBIS/INTEGRAL telescope, we have analyzed all the archival data of the telescope available at the time of writing the paper (the observations from January 2003 to April 2009). We have detected 834 hard (15-25keV) X-ray bursts, 239 of which were simultaneously recorded by the JEM-X/INTEGRAL telescope in the standard X-ray energy range. More than 70% of all bursts (587 events) have been recorded from the well-known X-ray burster GX 354-0. We have found upper limits on the distances to their sources by assuming that the Eddington luminosity limit was reached at the brightness maximum of the brightest bursts.
- ID:
- ivo://CDS.VizieR/J/PAZh/32/508
- Title:
- Hard X-ray Bursts by INTEGRAL in 2003-2004
- Short Name:
- J/PAZh/32/508
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- All of the observations performed with the IBIS telescope onboard the INTEGRAL observatory during the first one and a half years of its in-orbit operation (from February 10, 2003, through July 2, 2004) have been analyzed to find X-ray bursts. The time history of the IBIS/ISGRI total count rate in the energy range 15-25keV revealed 1077 bursts of durations from 5 to 500s with a high statistical significance (over the entire period of observations, only one event could be detected by chance with a probability of 20%). A part from the events associated with cosmic gamma-ray bursts (detected in the field of view or passed through the IBIS shield), solar flares, and activity of the soft gamma repeater SGR 1806-20, we were able to localize 105 bursts and, with one exception, to identify them with previously known persistent or transient X-ray sources (96 were identified with known X-ray bursters). In one case, the burst source was a new burster in a low state that received the name IGR J17364-2711. Basic parameters of the localized bursts and their identifications are presented in the catalog of bursts. Curiously enough, 61 bursts were detected from one X-ray burster, GX 354-0. The statistical distributions of bursts in duration, maximum flux, and recurrence time have been analyzed for this source. Some of the bursts observed with the IBIS/ISGRI telescope were also detected by the JEM-X telescope onboard the INTEGRAL observatory in the standard X-ray energy range 3-20keV.
- ID:
- ivo://CDS.VizieR/J/PAZh/30/589
- Title:
- Hard X-ray catalog of Sagittarius arm
- Short Name:
- J/PAZh/30/589
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The images of the Sagittarius arm tangent obtained with the IBIS telescope of the INTEGRAL observatory in the energy range 18-120keV during their observations in the spring of 2003 are analyzed.
- ID:
- ivo://CDS.VizieR/J/AJ/125/2239
- Title:
- Hard X-ray emission from white dwarfs
- Short Name:
- J/AJ/125/2239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Inspired by the hard X-ray emission from WD 2226-210, the central star of the Helix Nebula, we have made a systematic search for similar sources by correlating the white dwarf catalog of McCook & Sion (1999, See Cat. <III/235>) and the ROSAT Position Senstive Proportional Counter (PSPC) point-source catalog of White et al. (2000, Cat. <IX/31>). We find 76 white dwarfs coincident with X-ray sources at a high level of confidence. Among these sources, 17 show significant hard X-ray emission at energies greater than 0.5keV. Twelve of these white dwarfs with hard X-ray emission are in known binary systems, in two of which the accretion of the close companion's material onto the white dwarf produces hard X-ray emission, and in the other 10 the late-type companions' coronal activity emits hard X-rays. One apparently single white dwarf is projected near an active galactic nucleus that is responsible for the hard X-ray emission. The remaining four white dwarfs and two additional white dwarfs with hard X-ray emission appear single.
- ID:
- ivo://CDS.VizieR/J/AJ/127/477
- Title:
- Hard X-ray emissions of white dwarfs
- Short Name:
- J/AJ/127/477
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have previously conducted a search for X-ray sources coincident with white dwarfs using the white dwarf catalog compiled by McCook & Sion (1999, Cat. <III/210>, <III/235>) and the ROSAT sources in the WGA (<IX/31>) Catalog (Paper I, O'Dwyer et al., 2003AJ....125.2239O). To include the white dwarfs discovered since 1999 and to include the X-ray sources detected in ROSAT Position Sensitive Proportional Counter (PSPC, <IX/30>) observations made with a boron filter, we have carried out another search using an updated list of white dwarfs and the final catalogs of the ROSAT PSPC observations with and without a boron filter. Forty-seven new X-ray sources convincingly coincident with white dwarfs are found and reported in this paper.
- ID:
- ivo://CDS.VizieR/J/ApJ/618/123
- Title:
- Hard X-ray-emitting AGNs
- Short Name:
- J/ApJ/618/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present X-ray and optical analysis of 188 active galactic nuclei (AGN) identified from 497 hard X-ray (f_2.0-8.0keV_>2.7x10-15ergs/cm^2^/s) sources in 20 Chandra fields (1.5{deg}^2^) forming part of the Chandra Multiwavelength Project (ChaMP). These medium depth X-ray observations enable us to detect a representative subset of those sources responsible for the bulk of the 28keV cosmic X-ray background. Brighter than our optical spectroscopic limit, we achieve a reasonable degree of completeness (77% of X-ray sources with counterparts r'<22.5 have been classified): broad emission-line AGNs (62%), narrow emission-line galaxies (24%), absorption line galaxies (7%), stars (5%), or clusters (2%).
- ID:
- ivo://CDS.VizieR/J/ApJS/207/19
- Title:
- Hard X-ray survey from Swift-BAT 2004-2010
- Short Name:
- J/ApJS/207/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the catalog of sources detected in 70 months of observations with the Burst Alert Telescope (BAT) hard X-ray detector on the Swift gamma-ray burst observatory. The Swift-BAT 70 month survey has detected 1171 hard X-ray sources (more than twice as many sources as the previous 22 month survey) in the 14-195 keV band down to a significance level of 4.8{sigma}, associated with 1210 counterparts. The 70 month Swift-BAT survey is the most sensitive and uniform hard X-ray all-sky survey and reaches a flux level of 1.03x10^-11^erg/s/cm2 over 50% of the sky and 1.34x10^-11^erg/s/cm2 over 90% of the sky. The majority of new sources in the 70 month survey continue to be active galactic nuclei, with over 700 in the catalog.
- ID:
- ivo://CDS.VizieR/J/ApJS/186/378
- Title:
- Hard X-ray survey from Swift-BAT 2004-2006
- Short Name:
- J/ApJS/186/378
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the catalog of sources detected in the first 22 months of data from the hard X-ray survey (14-195keV) conducted with the Burst Alert Telescope (BAT) coded mask imager on the Swift satellite. The catalog contains 461 sources detected above the 4.8{sigma} level with BAT. High angular resolution X-ray data for every source from Swift-XRT or archival data have allowed associations to be made with known counterparts in other wavelength bands for over 97% of the detections, including the discovery of ~30 galaxies previously unknown as active galactic nuclei and several new Galactic sources. A total of 266 of the sources are associated with Seyfert galaxies (median redshift z~0.03) or blazars, with the majority of the remaining sources associated with X-ray binaries in our Galaxy. This ongoing survey is the first uniform all-sky hard X-ray survey since HEAO-1 in 1977 (Fishman G.J., 1977IAUC.3134....1F). Since the publication of the nine-month BAT survey (Tueller, 2008, Cat. <J/ApJ/681/113>) we have increased the number of energy channels from four to eight and have substantially increased the number of sources with accurate average spectra. The BAT 22 month catalog is the product of the most sensitive all-sky survey in the hard X-ray band, with a detection sensitivity (4.8{sigma}) of 2.2x10^-11^erg/cm^2^/s (1mCrab) over most of the sky in the 14-195keV band.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A70
- Title:
- Hard X-ray view of the soft excess in AGN
- Short Name:
- J/A+A/588/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An excess of X-ray emission below 1keV, called soft excess, is detected in a large fraction of Seyfert 1-1.5s. The origin of this feature remains debated, as several models have been suggested to explain it, including warm Comptonization and blurred ionized reflection. In order to constrain the origin of this component, we exploit the different behaviors of these models above 10keV. Ionized reflection covers a broad energy range, from the soft X-rays to the hard X-rays, while Comptonization drops very quickly in the soft X-rays. We present here the results of a study done on 102 Seyfert 1s (Sy 1.0, 1.2, 1.5 and NLSy1) from the Swift BAT 70-Month Hard X-ray Survey catalog. The joint spectral analysis of Swift/BAT and XMM-Newton data allows a hard X-ray view of the soft excess that is present in about 80% of the objects of our sample. We discuss how the soft-excess strength is linked to the reflection at high energy, to the photon index of the primary continuum and to the Eddington ratio. In particular, we find a positive dependence of the soft excess intensity on the Eddington ratio. We compare our results to simulations of blurred ionized-reflection models and show that they are in contradiction. By stacking both XMM-Newton and Swift/BAT spectra per soft-excess strength, we see that the shape of reflection at hard X-rays stays constant when the soft excess varies, showing an absence of link between reflection and soft excess. We conclude that the ionized-reflection model as the origin of the soft excess is disadvantaged in favor of the warm Comptonization model in our sample of Seyfert 1s.
