Does the Blazar Gamma-ray Spectrum Harden with Increasing Flux?-What We Learned From EGRET

Details Does the Blazar Gamma-ray Spectrum Harden with Increasing Flux?-What We Learned From EGRET Does the Blazar Gamma-ray Spectrum Harden with Increasing Flux?-What We Learned From EGRET

Jul 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aipc..921..353n&link_type=abstract

THE FIRST GLAST SYMPOSIUM. AIP Conference Proceedings, Volume 921, pp. 353-354 (2007).

Computer Science

Performance

Gamma-Ray Sources, Gamma-Ray Bursts, Active And Peculiar Galaxies And Related Systems, X- And Gamma-Ray Telescopes And Instrumentation

Scientific paper

The Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO) discovered gamma-ray emission from more than 67 blazars during its nine-year lifetime. We conducted an exhaustive search of the EGRET archives and selected all the blazars that have been observed multiple times and were bright enough to enable a spectral analysis using standard power-law models. The sample consists of 18 flat-spectrum radio quasars (FSRQs), 6 low-frequency-peaked BL Lacs (LBLs) and 2 high-frequency-peaked BL Lacs (HBL). We do not detect any clear pattern in the variation of spectral index with flux. Some of the blazars do not show any statistical evidence for variability. The spectrum hardens with increasing flux in a few cases. There is also evidence for a flux-hardness anticorrelation at low fluxes in five blazars. The well observed blazars (3C 279, 3C 273, PKS 0528+134, PKS 1622-297, PKS 0208-512) do not show any overall trend in the spectral dependence on flux but the sample shows a mixture of hard and soft states. Our analysis uses the EGRET skymaps that were regenerated to include changes in performance during the mission.

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