We have used the Very Large Array (VLA) to search for radio emission from the globular cluster G1 (Mayall-II) in M31. G1 has been reported by Gebhardt et al. to contain an intermediate-mass black hole (IMBH) with a mass of ∼2 × 104 M⊙. Radio emission was detected within an arcsecond of the cluster center with an 8.4 GHz power of 2 × 10 15 W Hz-1. The radio/X-ray ratio of G1 is a few hundred times higher than that expected for a high-mass X-ray binary in the cluster center, but is consistent with the expected value for accretion onto an IMBH with the reported mass. A pulsar wind nebula is also a possible candidate for the radio and X-ray emission from G1; future high-sensitivity VLBI observations might distinguish between this possibility and an IMBH. If the radio source is an IMBH, and similar accretion and outflow processes occur for hypothesized ∼1000 M⊙ black holes in Milky Way globular clusters, they are within reach of the current VLA and should be easily detectable by the Expanded VLA when it comes on line in 2010.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
- Accretion, accretion disks
- Galaxies: individual (M31)
- Globular clusters: individual (G1)
- Radio continuum: galaxies