SIMBAD references

With a goal of searching for accreting intermediate-mass black holes (IMBHs), we report the results of ultra-deep Jansky Very Large Array radio continuum observations of the cores of three Galactic globular clusters: M15, M19, and M22. We reach rms noise levels of 1.5-2.1 µJy/beam at an average frequency of 6 GHz. No sources are observed at the center of any of the clusters. For a conservative set of assumptions about the properties of the accretion, we set 3σ upper limits on IMBHs from 360 to 980 M _☉. These limits are among the most stringent obtained for any globular cluster. They add to a growing body of work that suggests either (1) IMBHs ≳ 1000 M_☉ are rare in globular clusters or (2) when present, IMBHs accrete in an extraordinarily inefficient manner.