110 research outputs found
ROXA: a new multi-frequency selected large sample of blazars with SDSS and 2dF optical spectroscopy
Context. Although Blazars are a small fraction of the overall AGN population
they are expected to be the dominant population of extragalactic sources in the
hard X-ray and gamma-ray bands and have been shown to be the largest
contaminant of CMB fluctuation maps. So far the number of known blazars is of
the order of several hundreds, but the forthcoming AGILE, GLAST and Planck
space observatories will detect several thousand of objects of this type. Aims.
In preparation for these missions it is necessary to identify new samples of
blazars to study their multi-frequency characteristics and statistical
properties. Methods. We compiled a sample of objects with blazar-like
properties via a cross-correlation between large radio (NVSS, ATCAPMN) and X-
ray surveys (RASS) using the SDSS-DR4 and 2dF survey data to spectroscopically
identify our candidates and test the validity of the selection method. Results.
We present the Radio - Optical - X-ray catalog built at ASDC (ROXA), a list of
816 objects among which 510 are confirmed blazars. Only 19% of the candidates
turned out to be certainly non-blazars demonstrating the high efficiency of our
selection method. Conclusions. Our catalog includes 173 new blazar
identifications, or about 10% of all presently known blazars. The relatively
high flux threshold in the X-ray energy band (given by the RASS survey)
preferentially selects objects with high fx / fr ratio leading to the discovery
of new High Energy Peaked BL Lac (HBLs). Our catalog therefore includes many
new potential targets for GeV-TeV observations.Comment: 19 pages, 3 figure, 2 table
Blazar Counterparts for 3EG Sources at -40 < decl. < 0: Pushing South Through the Bulge
Supplementing existing survey data with VLA observations, we have extended
ray counterpart identifications down to decl. = -40 using our
Figure of Merit approach. We find blazar counterparts for 70% of EGRET
sources above decl. = -40 away from the Galaxy. Spectroscopic
confirmation is in progress, and spectra for two dozen sources are
presented here. We find evidence that increased exposure in the bulge region
allowed EGRET to detect relatively faint blazars; a clear excess of non-blazar
objects in this region however argues for an additional (new) source class.Comment: ApJ accepte
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