EXOSAT Observations of the X-Ray Binary Pulsar 4U 1538-52

Abstract

Results are reported from a temporal and spectral analysis performed on four EXOSAT observations, part of which were taken from the EXOSAT archive, carried out during March and August 1984. In the first observation an absorbing episode was detected, which may be attributed to an inhomogeneity in the stellar wind of QV Nor; the scale height of this blob is 2 x 10 exp 9 - 2 x 10 exp 10 cm, assuming a blob velocity of 100-1000 km/s, of the same kind of inhomogeneities observed in the Vela X-1 system. On the basis of an eclipse transition time of about 0.06 d, a scale height of about 1.5 x 10 exp 11 cm is confirmed for the atmosphere of the optical counterpart. The source exhibits prominent aperiodic time variability: the frequency spectra for the two observations out of eclipse are well fitted by a power law plus a constant, with a slope of 1.63 +/- 0.09 and 1.73 +/- 0.07 for the March 17 and August 10 observations, respectively.