XMM-Newton Observations of IGR J00291+5934: Signs of a Thermal Spectral Component during Quiescence

Abstract

We present X-ray observations of the transient accretion-powered millisecond pulsar IGR J00291 +5934 during quiescence. IGR J00291 + 5934 is the first source among accretion-powered millisecond pulsars to show signs of a thermal component in its quiescent spectrum. Fitting this component with a neutron star atmosphere or a blackbody model we obtain soft temperatures (-64 and-110 eV, respectively). As in other sources of this class a hard spectral component is also present, comprising more than 60% of the unabsorbed 0.5-10 keV flux. Interpreting the soft component as cooling emission from the neutron star, we can conclude that the compact object can be spun up to millisecond periods by accreting only ≤0.2 M7odot;. © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.