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1st of February 2024
An ATCA image showing a newly discovered faint radio source at the centre of the globular cluster 47 Tuc
Ultra-deep ATCA imaging of 47 Tucanae reveals a central compact radio source
by Paduano et al.
Paduano et al. present the results of an ultra-deep radio continuum survey, containing ∼480 hours of observations, of the Galactic globular cluster 47 Tucanae with the Australia Telescope Compact Array. This is the deepest radio image of a globular cluster, and the deepest image ever made with the Australia Telescope Compact Array. They identify ATCA J002405.702-720452.361, a faint (6 micro-jansky at 7.25 GHz), flat-spectrum radio source that is positionally coincident with the cluster centre and potentially associated with a faint X-ray source. No convincing optical counterpart was identified. The team used radio, X-ray, optical, and ultraviolet data to show that explanations involving a background active galactic nucleus, a chromospherically active binary, or a binary involving a white dwarf are unlikely. The most plausible explanations are that the source is an undiscovered millisecond pulsar or a weakly accreting black hole. If the X-ray source is associated with the radio source, the fundamental plane of black hole activity suggests a black hole mass in the range 54--6000 solar masses, indicating an intermediate-mass black hole or a heavy stellar-mass black hole. The image above is the 7.25 GHz radio image of 47 Tuc. The RMS noise level in this image is ∼790 nJy/beam. The core radius of 47 Tuc is shown by the dashed red circle.

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