Abstract for Proposal 088403
Probing the variable nature of a new Ultraluminous X-Ray Source in NGC 3621
A new ULX was recently discovered in the nearby galaxy NGC 3621 in the
archival XMM-Newton data, which shows extremely marked variability -
unique among the known ULXs - reminiscent of the so-called heartbeats,
a type of variability pattern observed in only a handful of systems. The
archival data yielded contradictory information on the nature of the
compact object powering XMM J111816.0-324910, partly due to the limited
quality of the data, and to the limited understanding of the heartbeat
phenomenon. We propose a Target of Opportunity observation of XMM
J111816.0-324910 for a total of 120ks, to obtain a better understanding
of the properties of J1118 by means of detailed spectral and timing
analysis. This ToO will be triggered based on approved Swift observations.
Details on Observing Strategy and Trigger Criteria
We will be monitoring 4XMM J111816.0--324910 weekly with Swift. We will
trigger the XMM observation proposed here as soon as possible should
J1118 reach a luminosity of 1.0E+39 ers/s in the Swift/XRT data). Once the
observation is triggered, the fastest reaction time would be desirable,
as the transient and variable nature of the target offers no guarantee
that a given state (therefore a certain luminosity) will be maintained
for a long period of time.