The X-ray spectrum of the unusual neutron star X-ray binary SAX J2224.9+5421

We propose a 50ks XMMNewton observation of the unusual neutron star Xraybinary SAX J2224.9+5421. Our target was discovered by BeppoSAX/WFC when itexhibited a thermonuclear Xray burst. Followup observations aiming toconstrain the persistent emission were performed virgul8 h later and detected thesource at a 0.510 keV luminosity of L_Xvirgul1E33 erg/s. This is very peculiar sinceneutron star Xray binaries are generally considered to be in quiescence atluminosities of L_Xvirgul1E311E33 erg/s, while they display accretion outbursts withluminosities of L_Xvirgul1E341E38 erg/s. We propose for a detailed investigation ofthe Xray spectrum of SAX J2224.9+5421 to gain insight into its nature andextraordinary behavior. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]