New VLA low frequency observations of the SNR W44

CASTELLETTI G., DUBNER G.; BROGAN C.; KASSIM N. E.

Simposio; 35th COSPAR Scientific Assembly; 2004

COSPAR

The bright supernova remnant W44 has been imaged at 74 and 330 MHz using the VLA at unprecedented levels of angular resolution and sensitivity at these long wavelengths. Full three-dimensional wide field imaging techniques that take into account the non-coplanarity of the array at these low frequencies have been used to achieve high dynamic range images. Combining our new low frequency images with existing VLA data at 1.4 GHz, we investigate spectral index variations across the remnant. In particular, we utilize changes in the observed synchrotron radio spectrum near the pulsar PSR B1853+01, in the interior of W44, to that at the remnant´s periphery, to explore differences in the  energy spectra of the different particle populations. Previous X-ray observations of W44 carried out with Einstein, EXOSAT, ROSAT, and ASCA instruments have revealed that the X-ray emission is  confined inside the radio continuum shell and is mostly thermal in origin. Recent Chandra studies have shown that the associated pulsar wind nebula is extended in the north-south direction with an extent about half that of the radio emission. Also, the Chandra observations revealed a noticeable difference in spectral index between the hard emission from the pulsar (gamma  ~1.4) and the nebula (gamma ~2.2). A comparison between the new radio results and the X-ray data will also be presented.