EXOSAT observations of a quasar PKS 2135-147

Abstract

A study of X-ray emission from the low polarization quasar, PKS 2135-147 (PHL 1657), is presented based on the Exosat observations carried out on two occasions separated by a week in 1984. There is little evidence for any variations in the X-ray intensity on hourly time scales during either of the two observations. About 30 percent change in the soft X-ray (0.1-2 keV) intensity is, however, observed over a week. The observed X-ray spectral data is best fitted by a power law with a photon index Γ of 1.6±0.4 (error bars are with 90 percent confidence), and a line of sight column density consistent with the 21 cm observations. There is neither a detection of any significant low energy absorption within the quasar nor is there any evidence for soft X-ray excess.