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Submitted by Anonymous on Wed, 04/15/2015 - 16:55

This page provides links to several documents describing the properties and operations of the Astrosat CZT Imager:


A basic overall description of the CZT Imager is to be found in the CZTI chapter of the Astrosat Handbook,  A comparative table of all the Astrosat science payloads may be found here...


Instrument details and performance:


The CZT Imager consists of an array of 64 CZT detector modules. Each detector module is surrounded by a collimator, on which a Coded Aperture Mask is placed. A calibration housing containing alpha tagged X-ray sources is inserted between the collimator assembly and the detector plane.  A veto layer sits under the CZT detector.  Apart from the coded mask at the top of the imager, two additional one-dimensional coded masks are mounted laterally on one of the sides of the calibration housing.  The dimensions and the arrangement of these different sections are described in the document providing CZTI Geometric Details.


The CZT detectors of the payload communicate to the satellite via a Processing Electronics (PE) module. Satellite interfaces like power, telemetry (TM), tele-command (TC), commands through the Bus Management Unit (BMU), Data handling system (BDH) are all routed through the PE.  This unit also handles interfaces with other satellite subsystems such as the Charged Particle Monitor (CPM) and the LAXPC clock. A description of the PE and the details of the onboard software may be found in the Onboard Software Document.


The performance of the CZTI observed during the Test and Calibration runs conducted on ground is described in the CZTI Calibration Document.


Polarization capability:


Simulations and laboratory tests show that the CZTI will have the capability to measure the X-ray polarization of bright hard X-ray sources.  The technique employed is the measurement of azimuthal distribution of Compton-scattered events.  The application of this to the CZTI and its expected performance are described in two publications:  Chattopadhyay et al (2014) Experimental Astronomy 37, 555  and  Vadawale et al (2015) Astronomy and Astrophysics, in press.


Data Analysis Pipeline and Software:


CZTI data received at the ground station will undergo several levels of processing on its way to being released for science applications.  Processing at Level 0 (Raw telemetry) and Level 1 (reorganization into payload-specific streams) will be done at the ground station.  Level 1 data will then be further processed at the Payload Operations Centre (POC) located at IUCAA, and the Level 1 data, along with Level 2 products, will be released for science use.  Software used for Level 2 pipeline will also be released to the users, who can use this to generate custom products.  A brief description of the functionality of the Level 2 data analysis software is presented in the CZTI Level2 software description document.  An explanation of various coordinate transformations used in the Level 2 software is provided here...


Apart from the level 2 products pipeline, the CZTI data will also pass through routine health monitoring and calibration during the data processing at the POC.  The software suite for this, which was also used for ground calibration, is described in the CZTI calibration data processing document.

The standard pipeline software mentioned above implements simple schemes, best suited to uncrowded fields.  Spectral analysis in the presence of multiple sources of comparable strength in the field of view requires more sophisticated techniques for a Coded Mask instrument.  One method under development by the CZTI team involves an iterative Bayesian reconstruction, a brief description of which is provided here...