CZT Imager of ASTROSAT - Indian Institute of · PDF fileCZT Imager of ASTROSAT A. R. Rao UV...
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CZT Imager of ASTROSAT
A. R. RaoUV AND MULTIWAVELENGTH ASTRONOMY
WITH ASTROSAT, 2006 Sep 27 – 29, IIA , Bangalore
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Multi-wavelength studies (UV to X-rays)spectra, variability
Periodic and aperiodic variabilityBroad band XBroad band X--ray spectroscopyray spectroscopy
nonnon--thermal components, thermal components, cyclotron linescyclotron lines
SurveysAll-sky, Galactic plane, deep
Astrosat Science Objectives
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Cygnus X-1: Spectral components
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Wide band spectrum of a black hole candidate
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CZT: Hard X-ray detector of the future …..
Good energy resolutionGood efficiencyPixelated :
Moderate imagingBackground estimationAvoids source confusion
Background reductionGood spectroscopic detector
Note: Used up to now only as a gamma-ray imager
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Science requirements
Area comparable to recent high energy spectroscopic detectors (HEXTE; PDS : 800 cm2).
Emphasis on spectroscopyEnergy resolution < 5 % @ 60 keVIndividual pixel handling/ calibrationBackground reductionUse the pixel for bgd. estimation etc.Minimum mass
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CZT Module
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CZT Module characterization
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Specifications…Area 1024 cm 2 (+/- 20%)Pixels 16384
Pixel size 2.5 mm X 2.5 mm (5 mm thick)
Read-out ASIC based (128 chips of 128 channels)
Imaging method Coded Aperture Mask (CAM)
Field of View 17 X 17 deg2 (CAM) - > 100 keV5 X 5 (25 – 100 keV)1 X 1 (5 – 25 keV)
Angular resolution 8 arcmin (21 arcmin geometric)
Energy resolution 5% @ 100 keV
Energy range 5 – 100 keVUp to 1 MeV (Photometric)
Sensitivity 0.5 mCrab (5 sig; 10 4 s)
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Design considerations
Active Compton Background rejectionSimple shield – minimize massCollimator to reduce DCXRBQuadrant-wiseCooling requirements
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Major components
CZT detectors CsI(Tl) – anticoincidenceCollimator/ Coded Aperture MaskAlha-tagged sourceData handling system
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Background Reduction
New “Phoswich”combination ….
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CAM assem bly
Colimator hsg. assembly
Calibration hsg. assem bly
Mother board assembly
Details of a Quadrant
Detector Box Assembly
Size - 484 x 484 x 600 mm
Weight - 50 K gm
Collimators - 6 x 6 Degree, 17 x 17 DegreeGraded Shield Material – Tantalum + Aluminum (For Passive shielding)
Power- 50 Watts
Four Independent QuadrantsFour Independent Quadrants
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CZT BackgroundCZT Background
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Response to a point source
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Expected Count rates (per second; per quadrant)
Diffuse Cosmic backgroundCalibration source
10100
Crab Nebula (5 keV threshold) 200
Crab Nebula (10 keV threshold) 100
Veto triggered events 250
Maximum expected event rate 1000
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Output for each X-ray event
Trigger 1 bitPixel Address 16 bitsADC output 12 bits
Multi-hit 1 bitVeto trigger 1 bit
Veto ADC output 8 bitsALPHA trigger 1 bit
Total 39 bits + trigger
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House keeping data+5 V ; +10 V;
Veto HV ;Alpha voltage Temperature 1,2,3,4
Counter data:< E1; E1 – E2; > E2
Alpha, Veto Two Software Counters (< E1; E1-E2)
LLD = 5 KeV; E1 = 40 keV; E2 = 100 keV
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Detector
FPGA+RAM
Asynchronous to
Synchronous
80C32 based data handling
system
DUAL PORT RAM
DUAL PORT RAM
DUAL PORT RAM
80C86 based data handling
system
FPGAHBT
DATATO SSR
Tele command & power interface
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Conclusions ….
Individual event transfer (50 Mbytes per orbit) Continuous calibrationActive and passive shieldingGood energy spectrum of sources > 1 mCrab (about 1000 sources)Galactic X-ray binaries, transients, GRBs, Seyfert galaxies, blazars ….