A MULTIFREQUENCY RADIO STUDY OF THE SUPERNOVA REMNANT HB9

We present a new radio map of HB9 at 232 MHz made at the Beijing Astro nomical Observatory. We also present previously unpublished maps at 15 1 MHz, from the new Cambridge Low-Frequency Synthesis Telescope Survey , and at 3750 MHz, from the Effelsberg Telescope. These radio maps are compared with previously published maps at 408, 1420, and 2695 MHz, t hus providing the most complete frequency coverage for a spectral inde x study of a supernova remnant to date. Spectral index maps are constr ucted using the running T-T plot method. Several properties of spectra l index behavior are determined. The mechanisms which can most natural ly account for the observed behavior are: variable thermal electron de nsity near the rim causing variable low frequency absorption and spect ral flattening; and variable magnetic field near the rim and a curved electron spectrum causing variable high frequency steepening near the rim. A high spectral index region is likely associated with extended e mission from 4C46.09.