Exploring compact objects through X-ray polarimetry

In this project proposal, new insights are sought on celestial compact objects, including mass-accreting neutron stars and black holes, as well as pulsars, through the novel technique of X-ray polarimetry.

Observations will be conducted in 2022 on the Northern Sky and in 2023/4 on the Southern Sky, using the second generation balloon-borne hard X-ray polarimetry mission, XL-Calibur.

The spectropolarimetric measurements (~15-80 keV) will be unique in the hard X-ray band, and provide an order-of-magnitude improvement in sensitivity compared to previous missions.

This proposal is highly timely, since there there is strong synergy with the IXPE satellite mission for soft X-ray polarimetry (2-8 keV) which is scheduled for launch late in 2021/early 2022.

While broadband observations are important for X-ray timing and spectral studies, they are essential for polarisation studies where the change of polarisation fraction and angle with energy, rather than the absolute values at specific energies, reveals the geometry and physical properties of the emission region.

In this application, funding is primarily sought for the recruitment of a Ph.D. student who will conduct spectropolarimetric observations of a sample of archetypical compact objects, including the Crab pulsar and Cygnus X-1.