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Abstract: The hard X-ray polarimeter POLAR aims to measure the linear polarization ofthe 50-500 keV photons arriving from the prompt emission of gamma-ray burstsGRBs. The position in the sky of the detected GRBs is needed to determinetheir level of polarization. We present here a method by which, despite of thepolarimeter incapability of taking images, GRBs can be roughly localized usingPOLAR alone. For this purpose scalers are attached to the output of the 25multi-anode photomultipliers MAPMs that collect the light from the POLARscintillator target. Each scaler measures how many GRB photons produce at leastone energy deposition above 50 keV in the corresponding MAPM. Simulations showthat the relative outputs of the 25 scalers depend on the GRB position. Adatabase of very strong GRBs simulated at 10201 positions has been produced.When a GRB is detected, its location is calculated searching the minimum of thechi2 obtained in the comparison between the measured scaler pattern and thedatabase. This GRB localization technique brings enough accuracy so that theerror transmitted to the 100% modulation factor is kept below 10% for GRBs withfluence Ftot \geq 10^-5 erg cm^-2 . The POLAR localization capability willbe useful for those cases where no other instruments are simultaneouslyobserving the same field of view.



Author: E. Suarez-Garcia, D. Haas, W. Hajdas, G. Lamanna, C. Lechanoine-Leluc, R. Marcinkowski, A. Mtchedlishvili, S. Orsi, M. Pohl, N. P

Source: https://arxiv.org/







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