Observations of the Transient X-Ray Pulsar EXO 2030+375

The transient X-ray pulsar EXO 2030+375 has outburst nearly every periastron passage of its eccentric (e=0.419) 46 day orbit for the last 10 years. RXTE PCA observations in 1996 July indicate an unusual outburst structure, with an initial spike preceeding periastron, followed by the main outburst, lasting ~> 10 days. This structure closely resembles 2S 1845-024 in which the spike is interpreted as passage of the pulsar through its companion's circumstellar envelope from an inclined orbit. Infrared measurements indicate the companion's disk is becoming denser, which should translate to a change from global spin-down to spin-up. We propose monitoring observations of EXO 2030+375 to confirm the initial spike as a recurrent feature and to look for a reversal in the global trend.