The New Gamma-ray Pulsar PSR J2229+6114, its Pulsar Wind Nebula, and Comparison with the Vela Pulsar

Abstract

With a period of 51.6 ms and spin-down power 2.2x10^{37} erg s^{-1}, PSR J2229+6114 is a compelling identification for the EGRET source 3EG J2227+6122 in which error circle it resides. Striking features of the Chandra X-ray image are an incomplete elliptical arc and a possible jet, similar to the structures that dominate the appearance of the Vela PWN. Approximately 70% of the 2-10 keV X-ray emission comes from a centrally peaked, diffuse nebula of radius 100" with a power-law spectrum of photon index 1.45 +/- 0.19. The pulsar itself has a marginally harder spectrum with photon index 0.99 +/- 0.27. For an assumed distance of 3 kpc the ratio of X-ray luminosity to spin-down power of PSR J2229+6114 is only 8 x 10^{-5}. We discuss a model in which such inefficient X-ray emission is the signature of a highly magnetized pulsar wind that prevents an internal MHD shock, at the location of the X-ray arc, from strongly compressing the flow. The incomplete X-ray arc is consistent with beaming from a relativistic equatorial outflow, while a surrounding radio shell is probably the forward shock in the surrounding ISM. An MeV source at this location was previously detected by the COMPTEL experiment on CGRO. This, plus the flat X-ray spectrum in the 2-10 keV band, suggests that PSR J2229+6114 is one of the brightest pulsars at 1 MeV, even while it is inconspicuous at radio through X-ray wavelengths, and as steep as the Crab above 100 MeV. The apparent variety of broad-band spectra displayed by high-energy pulsars bolsters the theory that rotation-powered pulsars dominate the unidentified Galactic EGRET source population.