Date post: | 16-Mar-2018 |
Category: |
Documents |
Upload: | truongnguyet |
View: | 221 times |
Download: | 1 times |
INTRODUCTION to ASTROSAT
S N Tandon, IUCAA(Meeting : Adaptive Optics with Moderate‐sizes Telescopes,
August 22‐25, 2011, IUCAA, Pune)
Plan of the Talk
• Idea: multi‐wavelength observatory• Overall Specifications etc., Orbit• The Instruments• Ultraviolet imaging telescope (UVIT)• Schedule, Availability of observing time
Idea …
• Proposal for a satellite with wide coverage in X‐ray band, and in Ultraviolet originated before year 2000
• By ~ 2004 the idea was converted to definite parameters of the payloads.
S/C Orbit
• Height ~ 600 km: good life ‐‐ > 5 yrs• Inclination from equator 8‐10 deg. – low background, minimise effect of SAA
• Mass of S/C : ~ 1500 kg• Pointing accuracy: < 0.05 deg• Tracking: < 0.5”/s, and jitter < 0.3” rms
SpecificationsUVIT SXT LAXPC CZTI SSM
Detector photon counting X-ray CCD(at the focal plane)
Proportional counter CdZnTe detector array Position-sensitive proportional counter
Imaging / non-imaging
imaging imaging non-imaging Imaging imaging
Optics Twin Ritchey-Chretian Conical foil (~Wolter-I) mirrors
Collimator 2- D coded mask 1- D coded mask
Bandwidth 130-180 nm FUV200-300 nm NUV
320-550 nm
0.3 - 8 keV 3 - 100 keV 10 - 100 keV 2 – 10 keV
Geometric Area (cm2)
~ 880 250 10800 1000 ? 180
EffectiveArea (cm2)
15-50 (depends on filter) [email protected] keV200@1-2 keV
50@6 keV
6000 @5-30 keV2000 @ 100 keV
1000 (E>10 keV)?(mask -transmission?)
~40 @ 2 keV90 @ 5 keV (Xe gas) (mask -transmission?)
Sp. Res. 15-1000 A 2.5% at 6 keV 12% at 22 keVV
10% at 60 keV 19% at 6 keV
Field 28’ dia 0.350 (FWHM) 10 x 10 170 x 170 60 x 900
Angular Resolution
1.8 arcsec 3 - 4 arcmin(HPD)
~(1-5) arcmin (in scan mode only)
8 arcmin ~10 arcmin
Time res. 10 ms ~ 100 ms 10 microsec 1 ms 1 ms
Sensitivity( Obs. Time)
20th magnitude(5(200s) in FUV
10 microCrab(5 ) (10000 s)
0.1 milliCrab(3 (1000 s)
milliCrab(5 (10000s)
~30 milliCrab(3) ( 300s)
SXT
• Focussing Telescope• Wolter Type I • Reflectors: Nested layers of Conical Gold‐coated Al foils
• CCD for detecting X‐rays• Read rate ~ 1 s for the full frame, ~ 0.1 s for partial frame
• FWHM for point sources: ~ 3’
7 October 2011 8
Wolter Type I Optics: Principle
Angle of Incidence~ 90 deg
Au coated Al foils
CCD
SXT: FM Optics – Entrance Aperture
7 October 2011 9
SXT Structure with Optics (EQM) : in Container
7 October 2011 10
Optics
Deck Interface ting
7 October 2011 12
Effective Area of SXT (Telescope + FPCA)
7 October 2011 13
SXT::CCD Data (Eng. CCD +TIFR Electronics)5.9 and 6.4 keV peaks
Si escape peaks3.70 and 4.15 keV
Isolated pixels only
Resolution ~150 eV(2.5% at 6 keV)
LAXPC
• Three large proportional counters filled with Xe‐CH4 mixture at 1500 Torr pressure
• 0.05 mm thick mylar cover • Collimators limit field of view to ~1 deg • Gas purified during the long life in the orbit
LAX –Proportional Counter
VETO Wires To rejectbackground
Wires to detect X-rays: 5 Layers
LAX‐PC
Collimator
Energy Resolution:: LAXPC
LAXPC‐ Eff. Area
Modes of LAXPC
• Event mode I: records amplitude, time, and layer of each pulse ‐ a photon could give pulses in two layers
• Event mode II: as above but amplitude is not recorded
• Broad‐band Counting Mode: Histogram of Counts vs Pulse height is recorded for each layer; time bin can be few ms to few s
• Fast Count Mode: Counts in top layer every 160 microsec in four bands of pulse‐amplitude
CZT Imager
• Imaging with a coded mask and multi‐pixel CZT detector arrays
• Field 17 x 17 deg and 6 x 6 deg• Energy range: 10 – 100 keV• Area of detector arrays ~ 1000 sq cm (eff. Area ~ 50% ?)
• Angular resolution 8’• Time resolution 1 ms• CsI anticoincidence for rejection of ackground
Size - 484 x 484 x 600 mmWeight - 50 kgCollimators - 6 x 6 Degree, 17 x 17 DegreeShield Material – Tantalum + Aluminum (Passive shielding)
Power- 50 Watts
Four Identical Quadrants
CZT Imager
Array of 2.4 X 2.4 mm CSIDetectors
CsI anti-coincidence detectorto reject background
?
Scanning Sky monitor (SSM) 1-D coded mask position-sensitive proportional
counter • Design Specs
• Energy range 2-10 keV• Energy resolution 19% in 10 keV• Effective area: at 2 keV ~ 40 sq cm, at 5 keV ~ 90 sq cm
(transmission of the mask??) • Angular resolution 10’• Time resolution 1 ms• Field of view ~ 6° X 90° min • Sensitivity ~30 mCrab (10 min. integ.)
• Mass ~ 52 kg• Power (raw) : ~ 49W
Rotating platform
SSM1SSM3 or boom camera
Detector
Scanning Sky Monitor
Amplifiers Front end logic(1No.)
SSM2
UVIT
• Two telescopes, each of ~ 375 mm aperture• 3‐Channels: 130‐180 nm, 200‐300 nm, and 320‐550 nm
• Selection of filters in each channel• Slitless spect. in 130‐180 nm and 200‐300 nm,with a resolution ~ 100
• Intensified CMOS Photon count Imagers
UVIT
PRIMARY MIRROR
SECONDARY MIRROR
DOORS/SUN-SHIELDS
FiltersDetector
FUNCTIONAL SPECs of UVIT
• FIELD OF VIEW: ~ 28’• SELECTABLE FILTERS : ~ 100 A AND ~ 500 A• SPECTROSCOPY : ~ 100 res. in FUV/NUV• TEMPORAL RESOLUTION/
ACCURACY : ~ 5 ms• OBSERVING MODE : STARE • Peak Effective Area: ~ 15 sq cm in 130‐180 nm, and
~ 50 sq c in the other channels • SPATIAL RESOLUTION : <1.8 “ in UV
OPTICAL LAYOUT ‐‐ FUV CHANNELf/12 Cassegrain, ~ 380 mm aperture
/grating
OPTICAL LAYOUT – NUV & VISf/12 Cassegrain, ~ 380 mm aperture
/grating
PHOTO‐CATHODE & MCP
DETECTOR MODULECMOS-IMAGEREach 25 micron pixelis ~ 3” x 3”
Fibre-taper~ 3 : 1
Tip/Tilt effect
• Typical total exposure is 1000 s• Drifts etc. in 1000 s can be > 10”• In one second drift is < 0.2”
find aspect every second with UVIT • Jitter ( < 1 Hz? ) can be 0.3” rms, and
its effect is estimated by gyro signals• Take individual exposures of < 0.1 s• Estimate relative aspect every 0.1 s• Shift and add all the short exposures
Schedule
• Launch expected 3rd quarter 2012• 6 months for performance verification• 6 months guaranteed time for instrument teams
Observation TimeInstruments PV Phase
(6months)Guaranteed Time (next 6 months)
First Year Regular
observations
Second year Regular
observations
Third year Regular
observations X-ray Inst. Teams
67% 4 months 32.5% 20% -
UVIT Teams 33% 2 months 17.5% 10% -Indian proposals
- - 35% 45% 65%
International proposals
- - - 10% 20%
Canadian Team
- - 5% 5% 5%
LU Team - - 3% 3% 3%TOO - - 5% 5% 5%Calibration time
- - 2% 2% 2%
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 kgCollimators - 6 x 6 Degree, 17 x 17 DegreeShield Material – Tantalum + Aluminum (Passive shielding)
Power- 50 Watts
Four Independent Quadrants