Abstract
We present the result of a Chandra ACIS observation of the pulsar PSR B1853+01 and its associated pulsar wind nebula (PWN), embedded in the supernova remnant W44. A hard-band ACIS map cleanly distinguishes the PWN from the thermal emission of W44. The nebula is extended in the north-south direction, with an extent about half that of the radio emission. Morphological differences between the X-ray and radio images are apparent. Spectral fitting reveals a clear difference in spectral index between the hard emission from PSR B1853+01 (Γ ~ 1.4) and the extended nebula (Γ ~ 2.2). The more accurate values for the X-ray flux and spectral index are used to refine estimates for PWN parameters, including magnetic field strength, the average Lorentz factor γ of the particles in the wind, the magnetization parameter σ, and the ratio k of electrons to other particles.