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

Abstract

The COS B source 2CG 135+01 has been observed by the EGRET instrument on 10 different occasions during the first ~52 months of the Compton Gamma Ray Observatory mission. The source is detected in all but one of the observations. For that one, the exposure was inadequate. The only likely source that is spatially coincident with the gamma-ray position is the radio source GT 0236+610/LS I +61°303. However, there is no compelling evidence for time variations in the gamma-ray emission associated with the radio outbursts from GT 0236+610. Spectral determinations on a timescale of a few days also give no strong evidence for a spectral variation associated with the radio emission of GT 0236+610. Such fluctuations might be expected based on models involving a compact object in an elliptical binary orbit about a massive star. The search for correlations simultaneous with the 8.4 GHz radio outbursts were supported by coordinated observations with the Madrid Deep Space Network during one of the exposures and by Green Bank Interferometer observations on two others. Although there is some possible variability in the gamma-ray flux, it is not clear that it is related to the radio phasing.