Supernovae and radio transients in M 82

TL;DR

This paper reports optical and infrared observations of supernovae in M 82, identifying a low-luminosity type II-P supernova and analyzing a radio transient, with implications for progenitor masses and transient nature.

Contribution

It provides detailed photometry and spectroscopy of SN 2004am and investigates radio transients, linking supernovae to their progenitors and transient phenomena in M 82.

Findings

SN 2004am was a highly reddened type II-P supernova.

Progenitor mass of SN 2004am estimated at 12+7/-3 Msun.

Detected a transient possibly linked to a microquasar.

Abstract

We present optical and near-infrared (IR) photometry and near-IR spectroscopy of SN 2004am, the only optically detected supernova (SN) in M 82. These demonstrate that SN 2004am was a highly reddened type II-P SN similar to the low luminosity type II-P events such as SNe 1997D and 2005cs. We show that SN 2004am was located coincident with the obscured super star cluster M 82-L, and from the cluster age infer a progenitor mass of 12 +7/-3 Msun. In addition to this, we present a high spatial resolution Gemini-N K-band adaptive optics image of the site of SN 2008iz and a second transient of uncertain nature, both detected so far only at radio wavelengths. Using image subtraction techniques together with archival data from the Hubble Space Telescope, we are able to recover a near-IR transient source co-incident with both objects. We find the likely extinction towards SN 2008iz to be not more than Av ~ 10. The nature of the second transient remains elusive and we regard an extremely bright microquasar in M 82 as the most plausible scenario.