1995A&A...293L..29M

The optical companion (V2116 Oph) of the X-ray pulsar GX 1+4 was observed on 1994 April 14 in the Hα region using the coude spectrograph and a CCD detector on the 1.9-m tdescope at Mount Stromlo Observatory. This observation formed part of an ongoing periodical monitoring of this source. A 3.5-fold increase in the Hα line intensity was seen at this time, compared to normal levels. The observed flux remained 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 the BATSE detectors on board CGRO indicated the presence of a 10 day long interval of X-ray flaring activity in GX 1+4, which ended 2-3days prior to our observation of high Her flux. We argue that enhanced Hα emission most likely results from the reprocessing of soft X-rays produced in the accretion disk around the neutron star in this symbiotic 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.