The Orbit of the Binary X-Ray Pulsar 4U 1538−52 from [ITAL]Rossi X-Ray Timing Explorer[/ITAL] Observations

Abstract

Improved orbital parameters of the high-massbinary X-ray pulsar 4U 1538-52 have been derived from high count ratedata obtained from the Rossi X-Ray Timing Explorer. Pulse-timinganalysis yields an eccentricity of 0.174+/-0.015, a periastron at64 deg +/-9 deg, and evidence of orbital decay withP orb /P orb = (-2.9 +/- 2.1) � 10 -6 yr -1.