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Session 99 - Blazars.
Display session, Thursday, January 16
We demonstrate a new way to search for blazars by correlating the positions of gamma ray sources from the Second EGRET Catalog (2EG) and polarized radio sources from the National Radio Astronomy Observatory Very Large Array Sky Survey (NVSS). Using the NVSS, we have investigated the radio polarization properties of blazars from Angel and Moore 1980 and concluded that blazars have a characteristic radio polarization at 1.4 GHz, P_1.4 > 1%. This is consistent with the conclusion of Angel and Moore that for most blazars, the polarization is significant, but generally weaker at radio than at optical wavelengths.
Our technique successfully re-confirms 13 of 18 known EGRET blazars using ``generous'' search radii and cuts of S_1.4 = 0.4 Jy and P_1.4 = 1%. When we apply the same procedure to unidentified and low-confidence identification sources of the 2EG, we find 12 possible associations, eight of which are unique to this work.
Of these eight, four identifications are possibly associated with optical counterparts. Furthermore, we have found four additional plausible associations for sources previously identified by Thompson et al.\ 1995 as AGN and suggest that their association of 2EG J1314+5151 with NVSS J1319+5148 is very unlikely since it has a steep spectrum.
Based on our success rate with previously identified gamma-ray AGN, we conclude that radio polarization properties are an important characteristic of blazars, and one which may be a particularly convenient characteristic in future work on blazar samples. Although in the past, primarily optical polarization and flat-spectrum properties were used to determine blazars, the existence of large, homogenous surveys makes radio polarization an important and potentially highly useful property to examine in the future.
This work has been supported by NASA contract NAG5-2163 (CGRO) to the Smithsonian Astrophysical Observatory.
Program listing for Thursday