NEW RADIO AND OPTICAL STUDY OF THE SUPERNOVA REMNANT W44

We present new optical images of the supernova remnant (SNR) W44 in th e H alpha and [S II] lines covering the entire source for the first ti me. We also report on improved radio image of W44 at 1442.5 MHz, obtai ned after the reprocessing of existing VLA data, A spectral index alph a of -0.4 was derived for the whole source, without indication of sign ificant spectral variations between 0.3 and 1.4 GHz across the remnant , Accurate multiwavelength comparisons were made based on existing obs ervations of W44 in the different spectral regimes. We find excellent correlation between optical and radio emission along the northwest bor der of the remnant, suggesting that the optical radiation is originati ng through radiative cooling of the shocked gas immediately behind the shock front. Some diffuse optical emission is also observed towards t he interior of W44, with no clear radio counterpart. We confirm that o ver most of the source, the bright X-ray emission corresponds with reg ions of low radio brightness. At the northern border of the remnant, d iffuse X-ray emission exactly overlaps the radio and optical radiation . From the study of the immediate environs of W44 we conclude that the remnant is interacting with molecular clouds along the eastern border , Such a scenario is compatible with the filamentary structure of W44, the excitation of OH masers and the apparent lack of optical emission along the eastern border. To the north, an extended atomic cloud surr ounds the remnant, although the interaction is not evident in this cas e. (C) 1997 American Astronomical Society.