Observations of the bright radio transient in M82: a new radio supernova?

ATel #2060; R. J. Beswick, T. W. B. Muxlow, A. Pedlar (JBCA, Manchester), D. Fenech (UCL), R. Fender, T. Maccarone (Southampton)
on 27 May 2009; 12:15 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Rob Beswick (Robert.Beswick@manchester.ac.uk)

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We report MERLIN radio observations of the recently announced radio transient and supernova candidate in M82. The radio transient was first detected on 2008 March 24 and reported by Brunthaler et al 2009 (ATEL#2020 & arXiv:0904.2388). Analysis of MERLIN observations taken between 1200UT 1st May and 1600UT 3rd May 2008 4994MHz shows the source to have a mean flux density of 117mJy. Over the duration of this observation the flux density of the new source increased from ~113mJy to ~119mJy. Using these high resolution observations (50mas) we measure the position of this new transient source to be at R.A. = 09h55m51s.5510., Decl. =+69o40'45".788. (equinox 2000.0; +/- 0".05 in each coordinate). Subsequent MERLIN observations, also at 4994MHz, show the flux density of this source has reduced to 28.5(+/- 2) mJy (observed 2009 April 30th to May 2nd using a 3-telescope subset of the MERLIN array) and 30.6 (+/- 1) mJy (2009 May 13th to 16th using the full MERLIN array). Previous observations at 4.7GHz with MERLIN on 3rd June 2007 and very deep observations at 4994MHz in April 2002 (Fenech et al 2009, MNRAS, 394, 1384) show no radio source at this position >0.3mJy/bm and >45microJy/bm (both 3-sigma) respectively. These observations along with those of Brunthaler et al., are consistent with this transient being a new radio SNe, and that our observations in May 2008 probably observed this source before it reached its initial radio peak at 4994MHz. Further radio observations of this source are underway.