Spin-Down Measurement of PSR J1852+0040 in Kesteven 79: Central Compact Objects as Anti-Magnetars

Using XMM-Newton and Chandra , we achieved phase-connected timing of the 105 ms X-ray pulsar PSR J1852+0040 that provides the first measurement of the spin-down rate of a member of the class of central compact objects (CCOs) in supernova remnants. We measure , and find no evidence for timing noise or variations in X-ray flux over 4.8 year. In the dipole spin-down formalism, this implies a surface magnetic field strength B s = 3.1 × 10 10 G, the smallest ever measured for a young neutron star, and consistent with being a fossil field. In combination with upper limits on B s from other CCO pulsars, this is strong evidence in favor of the "anti-magnetar" explanation for their low luminosity and lack of magnetospheric activity or synchrotron nebulae. While this dipole field is small, it can prevent accretion of sufficient fall-back material so that the observed X-ray luminosity of L x = 5.3 × 10 33 ( d /7.1 kpc) 2 erg s −1 must instead be residual cooling. The spin-down luminosity of PSR J1852+0040, erg s −1 , is an order of magnitude smaller than L x . Fitting of the X-ray spectrum to two blackbodies finds small emitting radii, R 1 = 1.9 km and R 2 = 0.45 km, for components of kT 1 = 0.30 keV and kT 2 = 0.52 keV, respectively. Such small, hot regions are ubiquitous among CCOs, and are not yet understood in the context of the anti-magnetar picture because anisotropic surface temperature is usually attributed to the effects of strong magnetic fields.