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 < 7 × 10 -14 s s -1 and no evidence for binary orbital motion. The implied energy loss rate is < 2 × 10 36 ergs s -1 , the surface magnetic field strength is B p < 3 × 10 12 G, and the spin-down age is τ > 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 ≈ 0.9 km, and L bol = 3.7 × 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, c ≈ 4 × 10 36 ergs s -1 . The age discrepancy implies that its has always been below 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 B p 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.