The Pulsar Wind Nebula Around PSR B1853+01 in the Supernova Remnant W44

We present radio observations of a region in the vicinity of the young pulsarPSR B1853+01 in the supernova remnant W44. The pulsar is located at the apex ofan extended feature with cometary morphology. We argue on the basis of itsmorphology and its spectral index and polarization properties that this is asynchrotron nebula produced by the spin down energy of the pulsar. The geometryand physical parameters of this pulsar-powered nebula and W44 are used toderive three different measures of the pulsar's transverse velocity. A range ofestimates between 315 and 470 km/s are derived, resulting in a typical value of375 km/s. The observed synchrotron spectrum from radio to X-ray wavelengths isused to put constraints on the energetics of the nebula and to derive theparameters of the pulsar wind.Comment: ApJ Let (in press