A puzzling event during the X-ray emission of the binary system GX 1+4

Abstract

We report on a long X-ray observation of the slow-rotating binary pulsar GX 1+4. BeppoSAX observed, in the 0.1-200 keV energy range, an event in which the source flux dropped for almost a day, and then recovered. During this event only the highenergy emission was found to be pulsed and the pulsations were shifted in phase of ∼ 0.2. The spectrum during the event was well fitted by a Compton-reflection model. A broad iron line at ∼ 6.55 keV was present outside of the event, where instead two narrow emission lines at ∼ 6.47 keV and ∼ 7.05 keV were detected. The pulse profile was highly variable as a function of both energy and time. We interpret this low-flux event as an occultation of the direct X-ray emission, due to the increase of a torus-like accretion disk; we then discuss similarities between this source and the recently discovered highly absorbed INTEGRAL sources.