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The Evolution of Swift/BAT Blazars and the Origin of the MeV Background
We use three years of data from the Swift/Burst Alert Telescope (BAT)survey to select a complete sample of X-ray blazars above 15 keV.This sample comprises 26 flat-spectrum radio quasars (FSRQs) and 12 BLLacertae (BL Lac) objects detected over a redshift range of 0.03 < z< 4.0. We use this sample to determine, for the first time in the15-55 keV band, the evolution of blazars. We find that, contrary tothe Seyfert-like active galactic nuclei (AGNs) detected by BAT, thepopulation of blazars shows strong positive evolution. This evolution iscomparable to the evolution of luminous optical quasi-stellar objects(QSOs) and luminous X-ray-selected AGNs. We also find evidence for anepoch dependence of the evolution as determined previously forradio-quiet AGNs. We interpret both these findings as a strong linkbetween accretion and jet activity. In our sample, the FSRQs evolvestrongly, while our best fit shows that BL Lac objects might not evolveat all. The blazar population accounts for 10%-20% (depending on theevolution of the BL Lac objects) of the cosmic X-ray background (CXB) inthe 15-55 keV band. We find that FSRQs can explain the entire CXBemission for energies above 500 keV solving the mystery of thegeneration of the MeV background. The evolution of luminous FSRQs showsa peak in redshift (zc = 4.3 ± 0.5) which is largerthan the one observed in QSOs and X-ray-selected AGNs. We argue thatFSRQs can be used as tracers of massive elliptical galaxies in the earlyuniverse.
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
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