Flux density variations of radio sources in M82 over the last 3 decades

TL;DR

This study monitors radio sources in M82 over three decades, revealing that most supernova remnants have stable flux densities, while a few show variations likely caused by environmental changes.

Contribution

It provides a long-term analysis of flux density variations in M82's radio sources, identifying new sources and characterizing their variability over different timescales.

Findings

Most SNRs in M82 have constant flux densities (~95%).

Two sources exhibit short and medium-term flux variations.

New sources, including a supernova and a transient, were detected.

Abstract

This paper presents the results of the 2009-2010 monitoring sessions of the starburst galaxy M82, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN) at 5GHz and e-MERLIN at 6GHz. Combining several 5GHz MERLIN epochs to form a map with 33.0 uJy/bm noise level, 52 discrete sources, mostly supernova remnants and HII regions, are identified. These include three objects which were not detected in the 2002 5GHz MERLIN monitoring session: supernova SN2008iz, the transient source 43.78+59.3, and a new supernova remnant shell. Flux density variations, in the long (1981 to 2010), medium (2002 to 2010) and short (2009 to 2010) term, are investigated. We find that flux densities of SNRs in M82 stay constant in most of the sample (~95%). In addition, aside from SN2008iz and the well-known variable source 41.95+57.5, two sources display short and medium term variations over the period 2009-2010. These sources being among the most compact SNR in M82, these flux density variations could be due to changes in the circumstellar and interstellar medium in which the shocks travel.