  We present the current results of an investigation into M51 ULX-7, using
archival data from XMM-Newton, Chandra and NuSTAR, and optical and radio data
from HST and VLA. The source has a consistently hard power-law X-ray spectrum
and high short-term variability. This is unusual variability behaviour for a
ULX, as we would expect highly variable ULXs to have soft energy spectra. The
power spectrum features a break at ~1e-3 Hz, from low frequency spectral index
alpha=0.1 to high frequency spectral index alpha=0.8, analogous to the low
frequency break found in power spectra of black holes accreting in the low/hard
state. We do not observe a corresponding high frequency break, however taking
the white noise level as a frequency lower limit of the break, we can calculate
a black hole mass upper limit of 9.12e4 solar masses, assuming that the ULX is
in the low/hard state. While there is no radio detection, we find a flux
density upper limit of 87 micro-Jy/beam. Using the X-ray/radio fundamental
plane, we calculate a black hole mass upper limit of 1.95e5 solar masses.
Therefore, this ULX is consistent with being an IMBH accreting in the low/hard
state.
