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. Two observations of the pulsar taken 6 days apart yield an upper limit on its spin-down rate of Ṗ < 7 × 10 s s and no evidence for binary orbital motion. The implied energy loss rate is Ė < 2 × 10 ergs s, surface magnetic field strength is Bp < 3 × 10 12 G, and 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 kTBB = 0.44±0.03 keV, radius RBB ≈ 0.9 km, and Lbol = 3.7×10 33 ergs s 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, Ėc ≈ 4 × 10 36 ergs s. The age discrepancy implies that its Ė has always been below Ėc, perhaps a distinguishing property of the CCOs. Alternatively, the X-ray spectrum of PSR J1852+0040 suggests a low-luminosity AXP, but the weak inferred Bp field is incompatible with a magnetar theory of its X-ray luminosity. So far, we cannot exclude accretion from a fall-back 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. Subject headings: stars: neutron — pulsars: (CXOU J185238.6+004020, PSR J1852+0040) — supernova remnants: individual (Kes 79)