GeV Gamma-Ray Variability from the TeV Blazar PKS 2155-304
W. Thomas Vestrand
P. Sreekumar
J. Gregory Stacy
Abstract
We present EGRET observations of a major outburst of GeV gamma-ray
emission from the BL Lac PKS 2155-304. During those observations the
> 100 MeV flux exceeded the upper limit for the preceding
PKS 2155-304 observation by a factor of five and the highest flux previously
measured by a factor of three. The > 100 MeV gamma-ray flux also showed
evidence for variability on a timescale of 3.5 days. An outburst of
TeV gamma-rays was also detected contemporaneously from PKS 2155-304 by a ground-based
imaging Cherenkov telescope. ToO x-ray observations with RXTE and BeppoSAX, that were
initiated by the detection of the GeV outburst, found the x-ray
emission to be at the highest flux levels yet observed. Unlike the
major TeV/x-ray outbursts detected from Mrk 421 and Mrk 501, PKS
2155-304 therefore shows strong associated variability at GeV
energies. We briefly discuss the implications for our understanding of
TeV blazars.
File translated from TEX by TTH, version 2.32.
On 2 Aug 1999, 16:04.