Abstract Details

Name: Madhuri Siriprolu
Affiliation: Indian Institute of Science, UR Rao Satellite Centre
Conference ID: ASI2020_512
Title : Optimisation of Photoelectric Polarimeter for Medium Energy X-rays.
Authors and Co-Authors : Madhuri S.(1,2), Koushal V.(1), Radhakrishna V.(1) 1. Space Astronomy Group, UR Rao Satellite Centre, Bangalore. 2. Indian Institute of Science, Bangalore.
Abstract Type : Oral
Abstract Category : Instrumentation and Techniques
Abstract : X-ray polarimetry gives an insight about the various physical processes responsible for emission of X-rays like particle acceleration mechanisms, scattering geometries, strength of magnetic and gravitational fields. Polarimetric possibilities in Soft X-ray band (2-10 keV) had been widely explored so far with the GEM (Gas Electron Multiplier) based detectors in low Z gas mixtures. By extending this possibility to higher energy X-rays, polarization measurements from hard X-ray sources like accretion powered pulsars, black holes can be made. A hard X-ray polarimeter, sensitive up to few tens of keV, is also suitable to measure polarization from Solar Flares. We propose to design a GEM based Medium Energy Polarimeter (MEP) in the energy range 10-30keV based on TPC (Time Projection Chamber) principle. In TPC, image of electron cloud produced by photoelectron is deduced from 1D strip readout and time sampling of the induced signal from the arriving electrons on the strips. The photoelectron emission direction derived from the electron cloud image is used to estimate the polarization direction. ANSYS and GARFIELD simulations are carried out for the selection of gas mixture that covers the full energy range. Optimization of drift parameters like drift velocity, drift field, drift gap, pressure of the gas is carried out to cover the full energy range, arriving at a compromise between polarimetric performance and quantum efficiency at higher energies. Further, the track selection is being employed in reconstruction methods to maximize the sensitivity of the polarimeter. A hardware attempt will be done at URSC to test the results.