Radio spectrum of W44: signatures of SNR/molecular clouds interaction

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

Capilla del Monte, Córdoba, Argentina, 18 al 22 de septiembre

Congreso; 49a Reunión Anual de la Asociación Argentina de Astronomía; 2006

Observatorio Astronomico de Cordoba

We report on the results of long wavelength observations of theGalactic supernova remnant (SNR) W44 (G34.7-0.4) carried out using the Very Large Array (VLA) at 74 MHz (~4 m) and 324 MHz (~1m). Several works have proposed that W44 is interacting with neighboring molecular clouds. The new images of W44, obtained with unprecedented sensitivity and resolution at these low radio frequencies, have allowed us to perform a detailed study of the spectrum. From the comparison of the new observations with archival VLA data at 1442 MHz, we find a straight spectrum between 74 and 1442 MHz (alpha~ -0.5) in most of the bright filamentary structure ofW44. Two clear exceptions to this spectral behavior are observed toward the southeast and west portions of the source: a positive spectral component (0.0<alpha <+0.4) discovered between 74 and 324 MHz toward the southeast and a concave down spectral region on the bright portion of the SNR limb to the west. In the investigated radio frequencies, no evidence for a spectral connection between the pulsar wind nebula created by PSR B1853+01 and the surrounding SNR radio shell, is observed.