AAS 204th Meeting, June 2004
Session 23 Radio and X-ray Studies of AGN
Oral, Monday, May 31, 2004, 2:00-3:30pm, 603/605/607

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[23.01] Gamma-ray Blazars: A Multiwavelength Study

D. Sowards-Emmerd (Stanford, SLAC), R. W. Romani (Stanford), P. F. Michelson (Stanford, SLAC), J. S. Ulvestad (NRAO)

We have implemented a new method of identifying candidate blazar counterparts for gamma-ray sources from the Third EGRET (3EG) catalog, selecting flat spectrum radio sources, many with X-ray counterparts. This method was originally applied to all of the northern 3EG sources (\vertb\vert > 10 degrees). Subsequently, we extended the survey south to decl. = -40 degrees, creating a small 8.4 GHz VLA A-array survey targeting flat spectrum radio sources in the area covered by 3EG error boxes. Optical spectroscopy of candidates was obtained using the Hobby-Eberly Telescope. This survey has found dozens of new counterparts, increasing the fraction of 3EG sources (\vertb\vert > 10 degrees) with blazar identifications to nearly 70%. These new counterparts include sources extending to nearly double the redshift of the most distant 3EG IDs. Of equal interest, we find a subset of the 3EG catalog without any plausible blazar counterparts according to our selection criteria, which may represent a new population of gamma-ray emitters.

In preparation for the GLAST mission, we have also created a radio/X-ray selected sample with properties similar to the 3EG countparts, but outside the 3EG error contours. Further, in an effort to extend detection of gamma-ray sources below the 3EG threshold, we have developed a new technique to quantify the significance of variable gamma-ray flux at candidate positions. For example, the non-3EG selected radio candidates have a small but significant excess of flux over the random background. Finally, based on this work, we comment on the number of sources we expect GLAST to detect.

DSE acknowledges support by SLAC under DOE contract DE-AC03-76SF00515.

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