Mass-loss rate estimation for the massive binary 4U 1538-52/QV Nor

Abstract

We present an analysis of archival RXTE data of the X- ray binary source 4U 1538−52/QV Nor. The RXTE ob- servatory made one complete binary cycle observation on January 1997 and 2001, respectively. The X-ray con- tinuum data are well described by an absorbed Nega- tive Positive power laws Exponentials (NPEX) compo- nent modified by an iron emission line at 6.4 keV and a cyclotron absorption line at 20 keV. Using a simple spher- ically symmetric wind model to describe the X-ray ab- sorption variations as a function of orbital phase, we in- ferred a wind mass-loss rate from the companion star of (1.3 − 2.5) × 10−6 M⊙/yr. Our results are consistent with those obtained by the Ginga X-ray observatory. We have also analyzed X-ray flux variations over the binary orbit and we have found a sharp increase at orbital phase 0.34 in both set of data. However, the increase at orbital phase 0.66 is significantly different in the two observa- tions.