A DETAILED X-RAY INVESTIGATION OF PSR J2021+4026 AND THE γ-CYGNI SUPERNOVA REMNANT

Abstract

We have investigated the field around the radio-quiet $\\gamma$-ray pulsar,\nPSR J2021+4026, with a ~140 ks XMM-Newton observation and a ~56 ks archival\nChandra data. Through analyzing the pulsed spectrum, we show that the X-ray\npulsation is purely thermal in nature which suggests the pulsation is\noriginated from a hot polar cap with $T\\sim3\\times10^{6}$ K on the surface of a\nrotating neutron star. On the other hand, the power-law component that\ndominates the pulsar emission in the hard band is originated from off-pulse\nphases, which possibly comes from a pulsar wind nebula. In re-analyzing the\nChandra data, we have confirmed the presence of bow-shock nebula which extends\nfrom the pulsar to west by ~10 arcsec. The orientation of this nebular feature\nsuggests that the pulsar is probably moving eastward which is consistent with\nthe speculated proper motion by extrapolating from the nominal geometrical\ncenter of the supernova remnant (SNR) G78.2+2.1 to the current pulsar position.\nFor G78.2+2.1, our deep XMM-Newton observation also enables a study of the\ncentral region and part of the southeastern region with superior photon\nstatistics. The column absorption derived for the SNR is comparable with that\nfor PSR J2021+4026, which supports their association. The remnant emission in\nboth examined regions are in an non-equilibrium ionization state. Also, the\nelapsed time of both regions after shock-heating is apparently shorter than the\nSedov age of G78.2+2.1. This might suggest the reverse shock has reached the\ncenter not long ago. Apart from PSR J2021+4026 and G78.2+2.1, we have also\nserendipitously detected an X-ray flash-like event XMM J202154.7+402855 from\nthis XMM-Newton observation.\n