Phase‐resolved Spectroscopy of the Vela Pulsar withXMM‐Newton

Abstract

The ~104 yr old Vela Pulsar represents the bridge between the young Crab-like and the middle-aged rotation-powered pulsars. Its multiwavelength behavior is due to the superposition of different spectral components. We take advantage of the unprecedented harvest of photons collected by XMM-Newton to assess the Vela Pulsar spectral shape and to study the pulsar spectrum as a function of its rotational phase. As for the middle-aged pulsars Geminga, PSR B0656+14, and PSR B1055-52 (the ``Three Musketeers''), the phase-integrated spectrum of Vela is well described by a three-component model, consisting of two blackbodies (Tbb = [1.06 ± 0.03] × 106 K, Rbb = 5.1 km, TBB = 2.16 × 106 K, RBB = 0.73 km) plus a power law (γ = 2.2). The relative contributions of the three components are seen to vary as a function of the pulsar rotational phase. The two blackbodies have a shallow ~7%-9% modulation. The cooler blackbody, possibly related to the bulk of the neutron star surface, has a complex modulation, with two peaks per period, separated by ~0.35 in phase, the radio pulse occurring exactly in between. The hotter blackbody, possibly originating from a hot polar region, has a nearly sinusoidal modulation, with a single, broad maximum aligned with the second peak of the cooler blackbody, trailing the radio pulse by ~0.15 in phase. The nonthermal component, magnetospheric in origin, is present only during 20% of the pulsar phase and appears to be opposite to the radio pulse. XMM-Newton phase-resolved spectroscopy unveils the link between the thermally emitting surface of the neutron star and its charge-filled magnetosphere, probing emission geometry as a function of the pulsar rotation. This is a fundamental piece of information for future three-dimensional modeling of the pulsar magnetosphere.