Optical and X-ray outbursts of Be/X-ray binary system SAX J2103.5+4545

Abstract

Aims: The main goal of this study is to investigate the relationship between the optical and X-ray behaviours of the Be/X-ray binary system SAX J2103.5+4545. Methods: We present the relations between the Hα equivalent width, optical brightness and X-ray flux of the system, by analysing the optical photometric and spectroscopic observations together with the X-ray observations. Results: The X-ray outburst of the system occurred just after the optical outburst. The nearly symmetric Hα emission line profiles observed during the beginning of the optical outburst turn into asymmetric profiles with increased EWvalues during the dissipation of the Be disc. A correlation between the Hα emission line strength and the X-ray flux was found. The Hα line indicates the existence of an equatorial disc around the Be star. The Hα line changed from emission to absorption during the observation period. The observed double peaked HeI emission lines might come from the accretion disc of neutron star which is temporarily formed at the time of X-ray outburst. © ESO 2009.