  We present the results of long-term monitoring of the X-ray emission from the
ultraluminous X-ray source XMMUJ122939.9+075333 in the extragalactic globular
cluster RZ2109. The combination of the high X-ray luminosity, short term X-ray
variability, X-ray spectrum, and optical emission suggest that this system is
likely an accreting black hole in a globular cluster. To study the long-term
behavior of the X-ray emission from this source, we analyze both new and
archival Chandra and XMM-Newton observations, covering 16 years from 2000 to
2016. For all of these observations, we fit extracted spectra of RZ2109 with
xspec models. The spectra are all dominated by a soft component, which is very
soft with typical fit temperatures of T $\simeq$ 0.15 keV. The resulting X-ray
fluxes show strong variability on short and long timescales. We also find that
the X-ray spectrum often shows no significant change even with luminosity
changes as large as a factor of five.
