Abstract Details
| Name: Mithun N P S Affiliation: Physical Research Laboratory, Ahmedabad Conference ID: ASI2017_444 Title : In-flight Spectral Calibration of AstroSat CZT Imager Authors and Co-Authors : S. V. Vadawale (PRL), T. Chattopadhyay (PRL, Penn State Univ.), A. R. Rao (TIFR), D. Bhattacharya (IUCAA), A. Vibhute (IUCAA), V. B. Bhalerao (IUCAA), S. Sreekumar (VSSC) Abstract Type : Oral Abstract Category : Instrumentation and Techniques Abstract : Cadmium Zinc Telluride Imager (CZTI) on-board AstroSat is an imaging and spectroscopic instrument in the hard X-ray energy range of 20-200 keV. In CZTI, an array of pixellated CZT detector modules constitute the detecting element and coded aperture mask is employed for imaging as well as for simultaneous background measurement for spectroscopy. Extensive ground calibration was done to characterize the instrument response prior to the launch. Here we present the methodology employed in spectral extraction and response generation and the improvements in various aspects of the instrument spectral calibration using in-flight calibration observations. In CZTI, background subtracted source spectrum is obtained by using mask-weighting algorithm suitably adapted for peculiarities of the instrument like unequal pixel area. The mask-weighting method is very sensitive to source location relative to mask and detectors, hence we make use of this to measure the alignment of coded-mask with respect to the detector plane with multiple observations of bright sources like Crab. Background subtraction by mask-weighting is dependent on measurement of non-uniformity of background counts in the detector plane and multiple blank sky observations are used to obtain this. Detector gain is continuously monitored using on-board calibration source and these spectra are used to fine tune the pixel wise gain correction factors which were determined from ground calibration. After incorporating these improvements in response, crab spectrum was fitted with canonical power law model to verify the response matrix. Further deviations were empirically modeled to arrive at effective area correction factors for each quadrant of CZTI. |