EGRET Observations of the Gamma-Ray Source 2CG 135+01

The COS-B source 2CG 135+01 has been observed by the EGRET instrument on six different occasions during the first three phases of the Compton Observatory Mission (May 16, 1991 - 4 October 1994). Although the source is always present, there is evidence for time variations correlated with the elliptical binary system GT 0236+610. Spectral determinations on the time scale of a few days suggest a hardening associated with periastron passage compared with the quiescent case. This may be an indication of shoch acceleration at the boundary between the interacting winds of the binary companions. This supports a model first suggested by Maraschi and Treves in 1981 and refined and expanded by Tavani in 1995.