2016ApJ...825..134M

Pulsar wind nebulae (PWNe) provide unique opportunities to study relativistic pulsar winds and their interaction with the surrounding medium. G63.7+1.1 is an intriguing supernova remnant studied so far only at radio wavelengths and classified as a PWN candidate based on its nonthermal radio emission. We present the first X-ray study of G63.7+1.1, obtained with XMM-Newton and the Chandra X-ray Observatory, with the goal of detecting and studying the candidate PWN in X-rays and searching for the neutron star candidate. The peak of the X-ray emission lies approximately 1.'2 from the peak of the 21 cm continuum emission and is offset from the center of the X-ray nebula. The diffuse X-ray emission is irregularly shaped (4.'2 x 3.'2), unlike the nearly symmetric 8'-diameter radio nebula. Its X-ray spectrum is fit with a power-law model, yielding a photon index of {1.75}_{-0.3}^{+0.4} , a column density of (1.6±0.5) x 10²²/cm2, and an X-ray luminosity of ∼2 x 10³³ erg/s (0.5-10.0 keV) at a kinematic distance of 6 kpc. Several point-like sources were detected within the limit of the X-ray nebula. We present a study of their spectra, identifying 3XMM J194753.4+274357 (CXO J194753.3+274351) as a candidate for the location of the neutron star powering the nebula. Located in a dense environment, we estimate that G63.7+1.1 is old enough (>=8 kyr) for the reverse shock to have interacted with the PWN. This, together with the large size estimated from radio studies (∼14 pc) and the offset between the radio and X-ray peaks, suggests an evolved nebula, with the radio nebula being a "relic" PWN.