YOUNG CRAB-LIKE PULSARS AND LUMINOUS X-RAY SOURCES IN STARBURSTS AND OPTICALLY DULL GALAXIES

摘要

Recent Chandra observations of nearby galaxies have revealed a number of ultraluminous X-ray sources (ULXs) with super-Eddington luminosities, away from the central regions of nonactive galaxies. The nature of these sources is still debated. We argue that a fraction of them could be young, Crab-like pulsars, the X-ray luminosity of which is powered by rotation. We use the pulsar birth parameters estimated from radio pulsar data to compute the steady state pulsar X-ray luminosity distribution as a function of the star formation rate (SFR) in the galaxy. We find that ～10% of optically dull galaxies are expected to have a source withL_x approx> 10~(39) ergs s~(-1), while starburst galaxies should each have several of these sources. We estimate that the X-ray luminosity of a few percent of galaxies is dominated by a single bright pulsar with L_x approx> 10~(39) ergs s~(-1) roughly independently of its SFR. We discuss observational diagnostics that can help distinguish the young pulsar population in ULXs.