The Stellar X-Ray Polarimeter (SXRP) is the only orbiting X-ray polarimeter currently scheduled to be flown. It will be the only instrument available in the next decade able to extend x-ray observations to the full parameter space of the radiation. The primary processes which lead to polarized x-ray emission are non-thermal radiation and electron scattering of thermal x-rays in non spherically symmetric geometries. The degree and position angle of polarization from a source is highly dependent on the geometry of some feature of the source, (the feature can be the magnetic field, the scattering disk, etc.). Thus, polarization measurements provide a direct probe of the source geometry. Because the SXRP provides unique information about x-ray emission, it will enable us to make important statements about the properties of a variety of astrophysical sources.
Binary X-ray pulsars X-ray polarimetry will allow the study of the accretion geometry at the polar caps of magnetized neutron stars. Using the scattering polarimeter of the SXRP, we will be able to measure the x-ray polarization of Her X-1 in five pulse phase bins and three energy bins with an average minimum detectable polarization of 5 distinguish between the pencil and fan beam geometries. In addition, we will be able to measure the average polarization of a number of other X-ray binaries (Cen X-3, GX1+4, 4U1626-67, ...) to a level of a few percent in individual 105 second observations.
Supernovae remnants The only statistically significant (19 sigma) measurement of X-ray polarization of an astrophysical object was the 19 which verified the synchrotron nature of the emission. SXRP can extend this measurement to other supernova remnants.
Accretion disk sources
Compton scattering from an accretion disk can lead to X-ray polarization. Polarimetry can provide information on the disk geometry.
Black hole candidates Inertial frame dragging around a rotating black hole (Lense-Thirring effect) can lead to a polarization vector that rotates with energy. Observation of such an effect could lend support the presence of a black hole and test a previously untested prediction of general relativity.
Radio pulsars X-rays from radio pulsars are believed to be due to a synchrotron radiation. The emission mechanism for optical pulses is unknown. X-ray polarization measurements would allow a comparison with optical measurements, providing information on the optical emission mechanism.
Soft X-ray transients A large fraction of soft X-ray transients are black hole candidates. X-ray polarization measurements could help determine the nature of these sources.