SIMBAD references

In this Letter we discuss the recently discovered radio transient in the nuclear region of M82. It has been suggested that this source is an X-ray binary, which, given the radio flux density, would require an X-ray luminosity, L_X∼ 6 {x} 10⁴² erg/s if it were a stellar mass black hole that followed established empirical relations for X-ray binaries. The source is not detected in the analysis of the X-ray archival data. Using a 99 per cent confidence level upper limit we find that L_X ≤ 1.8 {x} 10³⁷ and 1.5 {x} 10³⁷ erg/s, using power law and disc blackbody models, respectively. The source is thus unlikely to be a traditional microquasar, but could be a system similar to SS 433, a Galactic microquasar with a high ratio of radio to X-ray luminosity.