Relativistic Iron Line Emission from the Neutron Star Low‐Mass X‐Ray Binary 4U 1636‐536

Abstract

We present an analysis of XMM-Newton and RXTE data from three observations of the neutron star LMXB 4U 1636-536. The X-ray spectra show clear evidence of a broad, asymmetric iron emission line extending over the energy range 4-9 keV. The line profile is consistent with relativistically broadened Fe Kα emission from the inner accretion disk. The Fe Kα line in 4U 1636-536 is considerably broader than the asymmetric iron lines recently found in other neutron star LMXBs, which indicates a high disk inclination. We find evidence that the broad iron line feature is a combination of several Kα lines from iron in different ionization states.