Physics & Astronomy Principal Research Scientist Herman Marshal, MIT Kavli Institute: "The Future of X-Ray Polarimetry in Astronomy"

I will present several projects to measure the X-ray polarizations of astronomical sources over the next 5-10 years. Previous observations were obtained in the 1970s for bright Galactic sources such as X-ray binaries and the Crab Nebula using a Bragg reflection from graphite crystals, limiting the measurements to 2.6 and 5.2 keV. Recently, a few detections have been reported using Compton scattering at hard X-rays. A newly approved NASA mission is the Imaging X-ray Polarization Explorer (IXPE). It would operate in the 2-8 keV range and is expected to launch in late 2020. It has an imaging capability, with a resolution of about a half arc-minute, and should detect X-ray polarizations as low as 1-5 percent for a dozen or more active galaxies, supernova remnants, neutron stars and X-ray binaries during a mission lifetime of a few years. I will describe the instrument and a few of the science goals. I will also describe a design for a sounding rocket-based polarimeter to work in the 0.2-0.6 keV band. The method uses gratings developed at MIT and multilayer coated mirrors. Potential targets include active galaxies, isolated neutron stars, and nearby black hole binaries in outburst. The configuration is extensible to orbital use, possibly to be combined with other instruments to provide a bandpass from 0.2 to 50 keV.