The Absence of Radio Emission from the Globular Cluster G1

James CA Miller-Jones, some graduate students Eight Others, Thomas Maccarone

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The detections of both X-ray and radio emission from the cluster G1 in M31 have provided strong support for existing dynamical evidence for an intermediate-mass black hole (IMBH) of mass (1.8 ± 0.5) × 104 M ⊙ at the cluster center. However, given the relatively low significance and astrometric accuracy of the radio detection, and the non-simultaneity of the X-ray and radio measurements, this identification required further confirmation. Here we present deep, high angular resolution, strictly simultaneous X-ray and radio observations of G1. While the X-ray emission (L X = 1.74+0.53 -0.44 × 1036 (d/750 kpc)2 erg s-1 in the 0.5-10 keV band) remained fully consistent with previous observations, we detected no radio emission from the cluster center down to a 3σ upper limit of 4.7 μJy beam-1. Our favored explanation for the previous radio detection is flaring activity from a black hole low-mass X-ray binary (LMXB). We performed a new regression of the "Fundamental Plane" of black hole acti
Original languageEnglish
Pages (from-to)L1
JournalAstrophysical Journal Letters
StatePublished - Aug 2012


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