BeppoSAX observations of the X-ray binary pulsar GX 1+4

摘要

We present here the timing and spectral properties of BeppoSAX observations of the binary X-ray pulsar GX 1+4 carried out in August 1996, March 1997, and August 2000. In the middle of the August 2000 observation, the source was in a rare low intensity state that lasted for about 30 hours. Though the source does not show pulsations in the soft X-ray band (1.0–5.5 keV) during the extended low state, pulsations are detected in 5.5–10.0 keV energy band of the MECS detector and in hard X-ray energy bands (15–150 keV) of the PDS instrument. Broad-band (1.0–150 keV) pulse averaged spectroscopy reveals that the best-fit model comprises of a Comptonized continuum along with an iron K emission line. A strong iron K emission line is detected for the first time in GX 1+4 during the extended low state of 2000 observation. The optical depth and temperature of the Comptonizing plasma are found to be identical during the high and low intensity states whereas the hydrogen column density and the temperature of the seed photons are higher during the low state.