An Algorithm to Calibrate and Correct the Response to Unpolarized Radiation of the X-Ray Polarimeter Onboard IXPE
John Rankin, Fabio Muleri, Allyn F. Tennant, Matteo Bachetti, E. Costa, Alessandro Di Marco, Sergio Fabiani, Fabio La Monaca, P. Soffitta, Antonino Tobia, A. Trois, Fei Xie, L. Baldini, Niccolò Di Lalla, Alberto Manfreda, Stephen L. O’Dell, M. Perri, Simonetta Puccetti, Brian D. Ramsey, C. Sgró, Martin C. Weisskopf
Abstract
Abstract The Gas Pixel Detector (GPD) is an X-ray polarimeter to fly onboard IXPE and other missions. To correctly measure the source polarization, the response of IXPE’s GPDs to unpolarized radiation has to be calibrated and corrected. In this paper, we describe the way such response is measured with laboratory sources and the algorithm to apply such correction to the observations of celestial sources. The latter allows to correct the response to polarization of single photons, therefore allowing great flexibility in all the subsequent analysis. Our correction approach is tested against both monochromatic and nonmonochromatic laboratory sources and with simulations, finding that it correctly retrieves the polarization up to the statistical limits of the planned IXPE observations.