8th HEAD Meeting, 8-11 September, 2004
Session 4 Jets and Blazars
Poster, Wednesday, September 8, 2004, 9:00am-10:00pm

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[4.25] Long Term Spectral Properties of Blazars in the Gamma-ray Region

G. Nandikotkur (University of Maryland, College Park), R. Mukherjee (Barnard College, Columbia University)

We have searched the entire EGRET archives (~ 9 years of data) and selected all blazars that were well observed and bright enough to enable spectral index extraction using power law models in the 30 MeV-10000 MeV range. The sample includes 8 flat spectrum radio quasars (FSRQ), 1 low frequency peaked BL Lac (LBL) and 1 high frequency peaked BL Lac (HBL). There is evidence of variability of spectral index with the gamma-ray flux (>100 MeV) in all of them, but the nature of correlation is not uniform across all blazars. While there is an overall hardening of spectral index with increasing flux for some of the blazars, there is no overall trend for the others inspite of variability. We will examine these results in the context of blazar-contribution to the extragalactic gamma-ray background.

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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.