The Advanced X-ray Timing Array (AXTAR) is a mission concept for X-ray timing
of compact objects that combines very large collecting area, broadband spectral
coverage, high time resolution, highly flexible scheduling, and an ability to
respond promptly to time-critical targets of opportunity. It is optimized for
submillisecond timing of bright Galactic X-ray sources in order to study
phenomena at the natural time scales of neutron star surfaces and black hole
event horizons, thus probing the physics of ultradense matter, strongly curved
spacetimes, and intense magnetic fields. AXTAR's main instrument, the Large
Area Timing Array (LATA) is a collimated instrument with 2-50 keV coverage and
over 3 square meters effective area. The LATA is made up of an array of
supermodules that house 2-mm thick silicon pixel detectors. AXTAR will provide
a significant improvement in effective area (a factor of 7 at 4 keV and a
factor of 36 at 30 keV) over the RXTE PCA. AXTAR will also carry a sensitive
Sky Monitor (SM) that acts as a trigger for pointed observations of X-ray
transients in addition to providing high duty cycle monitoring of the X-ray
sky. We review the science goals and technical concept for AXTAR and present
results from a preliminary mission design study.Comment: 19 pages, 10 figures, to be published in Space Telescopes and
Instrumentation 2010: Ultraviolet to Gamma Ray, Proceedings of SPIE Volume
773