Modeling the Surface X-ray Emission and Viewing Geometry of PSR J0821-4300 in Puppis A

TL;DR

This paper models the surface X-ray emission and viewing geometry of PSR J0821-4300, revealing hot-spot configurations, constraining angles, and providing insights into its magnetic field and temperature distribution.

Contribution

It introduces a detailed hot-spot model fitting the pulsar's spectrum and pulse profile, constraining geometry and magnetic field, and discusses implications for neutron star surface temperature distribution.

Findings

Hot-spot model explains double blackbody spectrum and pulse profile.

Constraints on hot-spot angles: (86°,6°) with errors, degenerate in two angles.

Upper limit on period derivative: Ṗ < 3.5×10⁻¹⁶, magnetic field B_s < 2×10¹¹ G.

Abstract

We show that a pair of thermal, antipodal hot-spots on the neutron star surface is able to fully account for the pulsar's double blackbody spectrum and energy-dependent pulse profile, including the observed 180 degree phase reversal at approximately 1.2 keV. By comparing the observed pulse modulation and phase to the model predictions, we strongly constrain the hot-spot pole (xi) and the line-of-sight (psi) angles with respect to the spin axis. For a nominal radius of R = 12 km and distance D = 2.2 kpc, we find (xi,psi) = (86d,6d), with 1-sigma error ellipse of (2d,1d); this solution is degenerate in the two angles. The best-fit spectral model for this geometry requires that the temperatures of the two emission spots differ by a factor of 2 and their areas by a factor of ~ 20. Including a cosine-beamed pattern for the emitted intensity modifies the result, decreasing the angles to (84d,3d); however this model is not statistically distinguishable from the isotropic emission case. We also present a new upper limit on the period derivative of Pdot < 3.5E-16 (2-sigma), which limits the global dipole magnetic field to B_s < 2.0E11 G, confirming PSR J0821-4300 as an "anti-magnetar." We discuss the results in the context of observations and theories of nonuniform surface temperature on isolated NSs of both weak and strong magnetic field. To explain the nonuniform temperature of PSR J0821-4300 may require a crustal field that is much stronger than the external, global dipole field.