Radio studies of supernovae 1979C, 1986J and 2006X with LOFAR

TL;DR

This study uses LOFAR radio observations to analyze supernovae SN 1979C, SN 1986J, and SN 2006X, revealing their long-term radio evolution, constraining circumstellar environments, and demonstrating LOFAR's capabilities in supernova research.

Contribution

First LOFAR observations of these supernovae providing new insights into their radio evolution and circumstellar environments, with detailed modeling and imaging.

Findings

SN 1979C detected with flux density 4.6 mJy nearly 40 years postexplosion

SN 1986J imaged with flux density 6.77 mJy at 0.146 GHz

Constraints on circumstellar density for SN 2006X and spectral analysis of SN 1986J

Abstract

We present LOw Frequency ARray (LOFAR) studies of supernovae SN 1979C, SN 1986J, and SN 2006X, focusing on new observations from the LOFAR Two-metre Sky Survey (LoTSS) and the International LOFAR Telescope (ILT). For Type Ia SN 2006X, we derive a 3$\sigma$ upper limit of 0.7 mJy at 0.146 GHz, and using radio emission models based on the CS15DD2 explosion model, we constrain the circumstellar density to $n_{\rm H} \lesssim 10$ cm$^{-3}$ for the microphysical parameters $\epsilon_{\rm rel} = \epsilon_{\rm B} = 0.01$. SN 1979C is clearly detected in the LoTSS image with a flux density of $4.6 \pm 0.36$ mJy nearly 40 years postexplosion. Modeling its radio evolution suggests a steep flux decay ($F_{\nu} \propto t^{-2.1}$) between 22 and 42 years, a break in the spectrum near 1.5 GHz possibly due to synchrotron cooling, a progenitor mass of $\sim 13$ solar masses, and a progressive steepening with velocity for the density slope of the supernova ejecta. Our findings for SN 1979C contradict scenarios involving central compact object emission, and we obtain X-ray temperatures close to those derived from recent observations. For SN 1986J, we present the first ILT image showing a flux density of $6.77\pm0.2$ mJy at 0.146 GHz. The spectral index of the shell emission is found to be $0.66\pm0.03$, consistent with previous estimates, although variations at low frequencies warrant further investigation. Our results highlight the power of LOFAR for studying long-term radio evolution in supernovae.