Soria et al. study the late-time evolution of the compact Type IIb supernova SN 2001ig in the spiral galaxy NGC 7424, with new and unpublished archival data from the ATCA and ASKAP. More than two decades after the SN explosion, its radio luminosity is showing a substantial re-brightening: it is now two orders of magnitude brighter than expected from the standard model of a shock expanding into a uniform circumstellar wind. This suggests that the SN ejecta have reached a denser shell, perhaps compressed by the fast wind of the Wolf-Rayet progenitor or expelled centuries before the final stellar collapse.

The image above shows the flux density of SN 2001ig at 2.4 GHz, 4.85 GHz and 8.55 GHz, based on ATCA observations, compared with a canonical evolution model. The pre-CABB ATCA data from 2001–2003 were taken at central frequencies of 2.4 GHz (red datapoints and dashed line model), 4.85 GHz (magenta datapoints and dash-dotted line model) and 8.55 GHz (blue datapoints and dotted line model), with a bandwidth of 128 MHz. The CABB era data from 2013, 2021 and 2024 were taken at central frequencies of 2.1 GHz, 5.5 GHz and 9 GHz and then rescaled to 2.4 GHz, 4.85 GHz and 8.55 GHz for the purposes of this plot. The bandwidth of the 2013, 2021 and 2024 measurements is 2 GHz. MJD (Modifed Julian Day) 52246 corresponds to the likely supernova explosion date of 2001 December 3.