AN X-RAY CORRELATED H-ALPHA FLARE IN GX-1+4

The optical companion (V2116 Oph) of the X-ray pulsar GX 1+4 was obser ved on 1994 April 14 in the H alpha region using the coude spectrograp h and a CCD detector on the 1.9-m telescope at Mount Stromlo Observato ry. This observation formed part of an ongoing periodical monitoring o f this source. A 3.5-fold increase in the H alpha line intensity was s een at this time, compared to normal levels. The observed flux remaine d 20 per cent above the ambient level during a subsequent observation made on 1994 May 12. An analysis of the daily X-ray data obtained by t he BATSE detectors on board CGRO indicated the presence of a 10 day lo ng interval of X-ray flaring activity in GX 1+4, which ended 2-3 days prior to our observation of high H alpha flux. We argue that enhanced H alpha emission most likely results from the reprocessing of soft X-r ays produced in the accretion disk around the neutron star in this sym biotic binary. This is the first time that a simultaneous optical and X-ray event has been reported in this system, confirming V2116 Oph as the companion to GX 1+4.