Detection of an unresolved nuclear radio source in M31

Abstract

An unresolved radio source with a flux density of 28 +/- 5 microJy has been detected at the center of the galaxy M 31. This source coincides with the optical stellar nucleus and with a variable Einstein X-ray source but is only 1/300 as luminous as the Galactic center source Sgr A and one fifth as luminous as Sgr A^*^. Consequently, this object is the weakest known nuclear radio source. No evidence is found for radio emission from the remnant of supernova 1885A in M31. An upper limit of 15 microJy (3 σ has been determined for the flux density of this source, which is 1/15 the value for Tycho's SNR if it were at the same distance. 2. The right ascension (J2000) given in Table 1 for the radio nucleus is incorrect. The correct right ascension (J2000) is 00^h^42^m^44.329^s^ +/- 0.15".