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4U0115+63 is a recurrent transient X-ray pulsar in a moderately eccentric orbit with a Be-star companion, V635 Cas. Many outbursts from this system have been reported over the past twenty years; yet despite the apparent relation between optical outbursts from the companion star and subsequent X-ray transient events, the physical mechanism for the mass transfer in the system remains unclear. We will present the results of analysis of observations made using BATSE during the April 1991 outburst from this system. This outburst does not fit the pattern of three year recurrence intervals previously suggested by Whitlock et al., (1989). The orbital elements of the system have been updated and will be compared to the results from 1987 Ginga observations (Tamura et al., 1992) in which evidence was presented for apsidal motion.
This work was supported by a NASA Compton Gamma Ray Observatory Guest Investigator grant, NAG 5-2032.
