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

Abstract

We present late time, low frequency observations of SN 2011dh made using the Giant Metrewave Radio Telescope (GMRT). Our observations at $325\mathrm{MHz}$, $610\mathrm{MHz}$ and $1280\mathrm{MHz}$ conducted between $93-421\mathrm{days}$ after the explosion supplement the millimeter and centimeter wave observations conducted between $4-15\mathrm{days}$ after explosion using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and extensive radio observations ($1.0-36.5\mathrm{GHz}$) conducted between $16-93\mathrm{days}$ after explosion using Jansky Very Large Array (JVLA). We fit a synchrotron self absorption model (SSA) to the $610\mathrm{MHz}$ and $1280\mathrm{MHz}$ radio light curves. We use it to determine the radius ($R_{\mathrm{p}}$) and magnetic field ($B_{\mathrm{p}}$) at $173$ \& $323$ days after the explosion. A comparison of the peak radio luminosity $L_{\mathrm{op}}$, with the product of the peak frequency $\hat{I}{½}_{\mathrm{p}}$ and time to peak $t_{\mathrm{p}}$ 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, $\dot{M}/v_{\mathrm{w}}$. We derive the mass loss parameter ($A_{\star }$) based on $610\mathrm{MHz}$ and $1280\mathrm{MHz}$ radio light curves, which are found to be consistent with each other within error limits.

9 pages, 2 tables and 6 figures. Under review. Comments are welcome