Abstract for Proposal 090284

Truncated Accretion Disks in Black Hole Binaries

We request 80 ks of XMM-Newton and 40 ks of NuSTAR time to trigger Target of Opportunity (ToO) observations of a new or known black hole transient during the end of its outburst, after the source has entered the low-hard state. We aim to obtain high signal-to-noise data during this fainter phase in order to measure the level of disk truncation using X-ray reflection spectroscopy. We will also provide measurements for the disk inclination, ionization and iron abundance. These observations will provide crucial constraints to support a large-scale data analysis program for these sources.

Details on Observing Strategy and Trigger Criteria
We will closely monitor both Swift-BAT and MAXI observations for known or new sources. For any source that shows a clear transition to the soft state, we will trigger once there is evidence of a decay phase and return to the hard state (typically indicated by a clear increase in the Swift BAT flux). Based on the history of known BHBs (typically 2-3 outbursts per year are observed), we expect roughly 1-2 sources to display a full outburst within the next cycle, setting a conservative triggering probably of 50%.