Discovery of a 105 ms X-ray pulsar in Kesteven 79: On the nature of compact central objects in supernova remnants

We report the discovery of 105 ms X-ray pulsations from the compact central object (CCO) in the supernova remnant Kes 79 using data acquired with the Newton X-Ray Multi-Mirror Mission (XMM-Newton). Two observations of the pulsar taken 6 days apart yield an upper limit on its spin-down rate of. P < 7 x 10(-14) s s(-1) and no evidence for binary orbital motion. The implied energy loss rate is. E < 2 x 10(36) ergs s(-1), the surface magnetic field strength is B-p < 3 x 10(12) G, and the spin-down age is tau > 24 kyr. The latter exceeds the remnant's estimated age, suggesting that the pulsar was born spinning near its current period. The X-ray spectrum of PSR J1852+ 0040 is best characterized by a blackbody model of temperature kT(BB) = 0: 44 +/- 0: 03 keV, radius R-BB approximate to 0.9 km, and L-bol = 3.7 x 10(33) ergs s(-1) at d = 7.1 kpc. The sinusoidal light curve is modulated with a pulsed fraction of > 45%, suggestive of a small hot spot on the surface of the rotating neutron star. The lack of a discernible pulsar wind nebula is consistent with an interpretation of PSR J1852+ 0040 as a rotation-powered pulsar whose spin- down luminosity falls below the empirical threshold for generating bright wind nebulae,. E-c approximate to 4 x 10(36) ergs s(-1). The age discrepancy implies that its. E has always been below. E-c, perhaps a distinguishing property of the CCOs. Alternatively, the X-ray spectrum of PSR J1852+ 0040 suggests a low-luminosity anomalous X-ray pulsar (AXP), but the weak inferred Bp field is incompatible with a magnetar theory of its X-ray luminosity. We cannot exclude accretion from a fallback disk. The ordinary spin parameters discovered from PSR J1852+ 0040 highlight the difficulty that existing theories of isolated neutron stars have in explaining the high luminosities and temperatures of CCO thermal X-ray spectra.