Abstract Details
| Name: Madhuri Siriprolu Affiliation: Indian Institute of Science Conference ID: ASI2018_1662 Title : Development and Studies on TPC GEM X-ray Polarimeter Authors and Co-Authors : Radhakrishna V.(1), Koushal V.(1), Meena.G(1), Monoj Bug(1), Anand Jain(1) 1.Space Astronomy Group, ISRO Satellite Center, Bangalore. Abstract Type : Contributed Talk Abstract Category : Instrumentation and Techniques Abstract : Large number of X-ray sources are expected to emit linearly polarized radiation either due to the emission processes (for example, synchrotron radiation) or due to the interaction of primary (un-polarized) photons with the matter surrounding them. We are developing a Gas Electron Multiplier (GEM) based X-ray polarimeter (E. Costa et.al., Nature 2011), which is an active area of interest for future astronomy missions, due to its higher sensitivity. This polarimeter works in soft X-ray band, and the X-ray photons in this range predominantly interact through photoelectric absorption. In this polarimeter, the aim is to generate an image of electron cloud produced along the photoelectron track and to reconstruct the photoelectron emission direction. We will present the design of GEM based X-ray polarimeter based on Time Projection Chamber (TPC) principle (J.K. Black et.al., NIMA 581 (2007)). In TPC, image of electron cloud produced by photoelectron is deduced from 1D strip readout and time sampling of the arriving electrons. The direction of emission of photoelectron is used to estimate the polarization direction. The emission direction is extracted from the projected 2D electron cloud image. It is observed that, we obtain tracks of varied length, size and distribution for different operating parameters. Hence, a detailed analysis of these tracks is essential in reconstructing the photoelectron emission angle. We adopted three different methods for reconstruction: Method of moments (R. Bellazzini et.al.,SPIE 4843(2003)), Estimating the photon interaction point (Baumgartner et.al.,SPIE 8443(2012)) and Improved method using variance/skewness conditions (Iwakiri et.al.,NIMA 838(2016)). These methods are being compared for different tracks and are analyzed taking into consideration each detailed case study and selection criteria are set. As a result, we propose a hybrid method which combines all these methods and optimizes the reconstruction, which can maximize the sensitivity of the polarimeter. |