Abstract for Proposal 094410

Searching for tightly-bound, transient X-ray binaries in the Galactic Center

We propose XMM ToO observations of new X-ray transients to be detected by the dailySwift/XRT monitoring in the central ~50 pc region of our Galaxy. As demonstratedfor one of the black hole transients, XMM can probe a population of tightly boundX-ray binaries (with short orbital periods < 12 hours) in the vicinity of Sgr A*,as predicted by recent N-body simulations and X-ray outburst history data.In addition, XMM can resolve Fe atomic features with the EPIC CCD spectrometers,including narrow Fe absorption lines formed in accretion disk winds fromhighly-inclined X-ray transients. The proposed XMM observations will provideimportant X-ray data allowing us to explore X-ray binary formation in the Galactic Center.

Details on Observing Strategy and Trigger Criteria
Our collaboration monitors the Galactic Center with Swift/XRT daily. Upon Swift/XRT detection of a new X-ray transient above Lx ~ 10^35 erg/s. We will trigger XMM observation as long as it falls into the XMM's visibility windows. We do not observe any of the six known NS-LMXBs within 25 arcmin from Sgr A* (e.g., AXJ J1745-2901). Historically, every 3 years on average, Swift has detected an X-ray transient that satisfies our criteria, i.e. a bright and long outburst that overlaps with the XMM?s visibility window.