Relativistic Iron Line Emission from the Neutron Star Low-mass X-ray Binary 4u 1636-536

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 K-α emission from the inner accretion disk. The Fe K-α 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 K-α lines from iron in different ionization states. Subject headings: accretion, accretion disks — binaries: close — stars: individual (4U 1636-536) — stars: neutron — X-rays: binaries — X-rays: stars