Polarization in the inner region of pulsar wind nebulae

¹ Astronomy Department, University of California at Berkeley, 601Campbell Hall, 94720 Berkeley, CA, USA e-mail: niccolo@astron.berkeley.edu
² Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E.Fermi 2, 50125 Firenze, Italy
³ INAF - Osservatorio Astrofisico di Arcetri, Largo E.Fermi 5, 50125 Firenze, Italy

Received: 20 June 2005
Accepted: 27 July 2005

Abstract

We present here the first effort to compute synthetic synchrotron polarization maps of Pulsar Wind Nebulae (PWNe). Our goal is to highlight how polarization can be used as an additional diagnostic tool for the flow structure in the inner regions of these nebulae. Recent numerical simulations suggest the presence of flow velocities ~ in the surroundings of the termination shock, where most of the high energy emission comes from. We construct polarization maps taking into account relativistic effects like Doppler boosting and position angle swing. The effect of different bulk velocities is clarified with the help of a toy-model consisting of a uniformly emitting torus. We also present a map based on recent numerical simulations of the entire nebula and compare it with presently available data. The comparison with upcoming high resolution observations could provide new insight into the inner structure of the nebula and put constraints on the geometrical properties of the magnetic field.