The pulsar wind nebula in G11.2-0.3

We present an X-ray and radio study of the wind nebula surrounding the central pulsar PSR J1811-1925 in the supernova remnant G11.2-0.3. Using high-resolution data obtained with the Chandra X-Ray Observatory and with the VLA radio telescope, we show the X-ray and radio emission is asymmetric around the pulsar, despite the latter's central position in the very circular shell. The new X-ray data allow us to separate the synchrotron emission of the pulsar wind nebula from the surrounding thermal emission and that from the pulsar itself. On the basis of X-ray data from two epochs, we observe temporal variation of the location of X-ray hot spots near the pulsar, indicating relativistic motion. We compare thermal emission observed within the shell, which may be associated with the forward shock of the pulsar wind nebula, to thermal emission from a nearby portion of the remnant shell, the temperature of which implies an expansion velocity consistent with the identification of the remnant with the historical event of 386 A.D. The measured X-ray and radio spectral indices of the nebula synchrotron emission are found to be consistent with a single synchrotron cooling break. The magnetic field implied by the break frequency is anomalously large, given the apparent size and age of the nebula, if a spherical morphology is assumed but is consistent with a bipolar morphology.