On the radio properties of the intermediate-mass black hole candidate
  ESO 243-49 HLX-1
  We present follow-up radio observations of ESO 243-49 HLX-1 from 2012 using
the Australia Telescope Compact Array (ATCA) and the Karl G. Jansky Very Large
Array (VLA). We report the detection of radio emission at the location of HLX-1
during its hard X-ray state using the ATCA. Assuming that the `Fundamental
Plane' of accreting black holes is applicable, we provide an independent
estimate of the black hole mass of $M_{\rm{BH}}\leq2.8^{+7.5}_{-2.1} \times
10^{6}$ M$_{\odot}$ at 90% confidence. However, we argue that the detected
radio emission is likely to be Doppler-boosted and our mass estimate is an
upper limit. We discuss other possible origins of the radio emission such as
being due to a radio nebula, star formation, or later interaction of the flares
with the large-scale environment. None of these were found adequate. The VLA
observations were carried out during the X-ray outburst. However, no new radio
flare was detected, possibly due to a sparse time sampling. The deepest,
combined VLA data suggests a variable radio source and we briefly discuss the
properties of the previously detected flares and compare them with microquasars
and active galactic nuclei.
