  LOFT-P is a concept for a NASA Astrophysics Probe-Class (<$1B) X-ray timing
mission, based on the LOFT concept originally proposed to ESAs M3 and M4 calls.
LOFT-P requires very large collecting area (>6 m^2, >10x RXTE), high time
resolution, good spectral resolution, broad-band spectral coverage (2-30 keV),
highly flexible scheduling, and an ability to detect and respond promptly to
time-critical targets of opportunity. It addresses science questions such as:
What is the equation of state of ultra dense matter? What are the effects of
strong gravity on matter spiraling into black holes? It would be optimized for
sub-millisecond timing to study phenomena at the natural timescales of neutron
star surfaces and black hole event horizons and to measure mass and spin of
black holes. These measurements are synergistic to imaging and high-resolution
spectroscopy instruments, addressing much smaller distance scales than are
possible without very long baseline X-ray interferometry, and using
complementary techniques to address the geometry and dynamics of emission
regions. A sky monitor (2-50 keV) acts as a trigger for pointed observations,
providing high duty cycle, high time resolution monitoring of the X-ray sky
with ~20 times the sensitivity of the RXTE All-Sky Monitor, enabling
multi-wavelength and multi-messenger studies. A probe-class mission concept
would employ lightweight collimator technology and large-area solid-state
detectors, technologies which have been recently greatly advanced during the
ESA M3 study. Given the large community interested in LOFT (>800 supporters,
the scientific productivity of this mission is expected to be very high,
similar to or greater than RXTE (~2000 refereed publications). We describe the
results of a study, recently completed by the MSFC Advanced Concepts Office,
that demonstrates that LOFT-P is feasible within a NASA probe-class mission
budget.
