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

BL Lacertae was detected by the EGRET instrument on the Compton Gamma Ray Observatory at the 10.2 sigma level with an average flux of (171 +/- 42) x 10(-8) photons cm(-2) s(-1), at energies greater than 100 MeV, during the optical outburst of 1997 July. This flux is more than 4 times the previously highest level. Within the July 15-22 observation there was a dramatic factor of 2.5 increase in the gamma-ray Aux on July 18.75-19.08, apparently preceding, by several hours, a brief optical flare, The gamma-ray flux decreased to its previous level within 8 hr, and the optical flux decreased to its prior level in less than 2 hr. The gamma-ray photon spectral index of 1.68 +/- 0.12 indicates that the spectrum during the 7 day observation was harder than the previous detection.