# Observational Constraints on Late-Time Radio Rebrightening of GRB-Supernovae

## TL;DR

This study searches for late-time radio rebrightening in three GRB-associated supernovae, constraining their remnant emission and surrounding medium density, and finds no significant rebrightening decades after explosion.

## Contribution

It provides the first deep limits on late-time radio emission from these supernovae, constraining models of SN remnant evolution and surrounding medium density.

## Key findings

- No detectable late-time radio rebrightening observed.
- Placed upper limits on radio luminosity 10-18 years post-explosion.
- Derived constraints on the density of the circumstellar medium.

## Abstract

We present a search for late-time rebrightening of radio emission from three supernovae (SNe) with associated gamma-ray bursts (GRBs). It has been previously proposed that the unusually energetic SNe associated with GRBs should enter the Sedov-Taylor phase decades after the stellar explosion, and this SN "remnant" emission will outshine the GRB radio afterglow and be detectable at significant distances. We place deep limits on the radio luminosity of GRB 980425/SN 1998bw, GRB 030329/SN 2003dh and GRB 060218/SN 2006aj, 10-18 years after explosion, with our deepest limit being $L_{\nu}$ $< 4 \times 10^{26}$ erg s$^{-1}$ Hz$^{-1}$ for GRB 980425/SN 1998bw. We put constraints on the density of the surrounding medium for various assumed values of the microphysical parameters related to the magnetic field and synchrotron-emitting electrons. For GRB 060218/SN 2006aj and GRB 980425/SN 1998bw, these density limits have implications for the density profile of the surrounding medium, while the non-detection of GRB 030329/SN 2003dh implies that its afterglow will not be detectable anymore at GHz frequencies.