Observations of a Correlated Gamma-Ray and Optical Flare for BL Lacertae

Abstract

The latest observations of BL Lacertae with the EGRET instrument on CGRO show that the gamma-ray flux was four times higher than the previous detection. Within the 1997 July 15-22 observation there was a dramatic factor of 2.5 increase in the gamma-ray flux, with a sharp peak of about 8 hours, and apparently preceding a brief optical flare by several hours. The gamma-ray photon spectral index was significantly harder than that for the previous detection.