Low frequency radio observations of SN 2011dh and the evolution of its post-shock plasma properties

We present late time, low frequency observations of SN 2011dh made using the Giant Metrewave Radio Telescope (GMRT). Our observations at $325 rm MHz$, $610 rm MHz$ and $1280 rm MHz$ conducted between $93-421 rm days$ after the explosion supplement the millimeter and centimeter wave observations conducted between $4-15 rm days$ after explosion using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and extensive radio observations ($ 1.0-36.5 rm GHz$) conducted between $16-93 rm days$ after explosion using Jansky Very Large Array (JVLA). We fit a synchrotron self absorption model (SSA) to the $610 rm MHz$ and $1280 rm MHz$ radio light curves. We use it to determine the radius ($R_{rm p}$) and magnetic field ($B_{rm p}$) at $173$ & $323$ days after the explosion. A comparison of the peak radio luminosity $L_{rm op}$, with the product of the peak frequency $ u_{rm p}$ and time to peak $t_{rm p}$ shows that the supernova evolves between the epochs of CARMA, JVLA and GMRT observations. It shows a general slowing down of the expansion speed of the radio emitting region on a timescale of several hundred days during which the shock is propagating through a circumstellar medium set up by a wind with a constant mass loss parameter, $dot M/v_{rm w}$. We derive the mass loss parameter ($A_{star}$) based on $610 rm MHz$ and $1280 rm MHz$ radio light curves, which are found to be consistent with each other within error limits.