Hard X-ray behaviour of Her X-1 during second main-on after the anomalous low state

Tata Institute of Fundamental Research, Mumbai, India

Corresponding author: ravi@tifr.res.in

Received: 16 July 2002
Accepted: 13 February 2003

Abstract

The binary X-ray pulsar Her X-1 shows a variety of time variations both in luminosity and its pulse features. For the first time an about 600 days long anomalous low state was seen in the light curve of ASM on board RXTE during the period MJD 51200-51800. We observed the source in the 20–200 keV energy band during its second main-on in the post anomalous state on November 21, 2000. The source was found to be extremely bright at high energies and a total of 26 000 photons from the source were detected during the 35 min snapshot observation. The cyclotron absorption line at ~34 keV and its second harmonics were clearly detected in the data. We present the spectral details and discuss its implication in terms of the geometrical properties of the source.