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) 60@0.5 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