Speaker
Description
Measurements of polarization of the X-ray emission in accreting neutron stars probe the particle acceleration region and can distinguish between fan-beam and pencil-beam approximations of the geometry of the accretion column.
In Dec 29th 2018, NASA’s hard X-ray polarimetry mission X-Calibur was launched on a 2.5-day stratospheric balloon flight from McMurdo station in Antarctica. During the campaign, X-Calibur observed the high-mass X-ray binary GX 301-2 in a rare flaring state at orbital phase ~0.35, close to apastron, resulting in a clear detection of GX 301-2 in the hard X-ray band. The ability of X-Calibur to measure the azimuthal scattering angle of the incoming X-rays resulted in a measurement of a 22% +/- 14% polarization fraction of the hard X-ray emission form GX 301-2 during the main peak of its 685s-long pulse profile. The measured polarization agrees better with fan-beam emission predictions (~20%) than pencil beam scenarios (~0%).
We will report on the results of the X-Calibur observations of GX 301-2 including a 15-60 keV light curve, hard X-ray energy spectrum, phase-resolved analysis, and constraints on linear polarization. We will also present contemporaneous observations of GX 301-2 in the soft X-ray band with the Neil Gehrels Swift observatory and NICER X-ray telescope that show significant variability of the shape of the pulse profile during the flaring event. We will conclude with a discussion of how neutron star, accretion, and fundamental physics can be constrained with future deeper polarimetric observations of accreting X-ray pulsars.
