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ASTROSAT: India's First Multi-Wavelength Space Observatory for Astrophysical Research

ASTROSAT, India’s first dedicated astronomical mission, launched by ISRO, offers a multi-wavelength approach for studying the universe. With a mass of 1.55 tons and operating in a near-equatorial orbit, it integrates various advanced instruments, including UV/Optical telescopes and large area X-ray detectors. Collaboratively built by ISRO and key institutions like TIFR, the mission enhances our ability to conduct simultaneous observations across multiple wavelengths, paving the way for breakthroughs in astrophysical research and providing invaluable data on cosmic phenomena.

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ASTROSAT: India's First Multi-Wavelength Space Observatory for Astrophysical Research

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  1. ASTROSAT: A Multi-Wavelength Satellite 1st Dedicated Indian Astronomical Mission ISRO Satellite Centre (ISAC), Bangalore Tata Institute of Fundamental Research, Mumbai University of Leicester Indian Institute of Astrophysics (IIA), Bangalore Inter-University Centre for Astronomy & Astrophysics (IUCAA), Pune. Canadian Space Agency Raman Research Institute, Bangalore Vikram Sarabhai Space Centre, Trivandrum X-RAY UV/Opt G.C.Stewart Berlin

  2. ASTROSAT(1.55 tons  600 kms, nearly equatorial orbit by PSLV, 3 gyros and 2 star trackers for attitude control by reaction wheel system with a Magnetic torquer ) 2 UV(+Opt ) Imaging Telescopes 3 Large Area Xenon Proportional Counters Soft X-ray Telescope Radiator Plates For SXT and CZT CZTI Scanning Sky Monitor (SSM) Folded Solar panels G.C.Stewart Berlin

  3. UVIT: Two Telescopes • f/12 RC Optics • Focal Length: 4756mm • Diameter: 38 cm • Simultaneous Wide Angle ( ~ 28’) images in FUV (130-180 nm) in one and NUV (180-300 nm) & VIS (320-530 nm) in the other • MCP based intensified CMOS detectors • Spatial Resolution : 1.8” • Sensitivity in FUV: mag. 20 in 1000 s • Temporal Resolution ~ 30 ms, full frame ( < 5 ms, small window ) • Gratings for Slit-less spectroscopy in FUV & NUV • R ~ 100 G.C.Stewart Berlin

  4. G.C.Stewart Berlin

  5. UVIT: filters G.C.Stewart Berlin

  6. GALEX UVIT FoV (Circular dia) 1.24 degrees 27 arc-min No. of bands 2 (NUV, FUV) 2 channels (NUV, FUV) + Vis Filters in NUV NIL 5 filters Filters in FUV NIL 5 filters [multiple colour-colour diagrams] Spectroscopy Grism Grating Resolution R ~ 100-120 R ~ 100 No. of grism/grating 1 per band 2 per band Angular resolution 4.5-6.0 arcsec 1.8 arc-sec (FWHM) Saturation < 10 mag < 8.0 mag (neutral density filter) [can image fields with bright objects] Time resolution ~ 10 milli-sec ~ 5.0 milli-sec (window mode) ~ 30 milli-sec full field G.C.Stewart Berlin

  7. Large Area Xenon Proportional Counter (LAXPC): Characteristics Energy Range : 3-80 keV (50 m Mylar window, 2 atm. of 90 % Xenon + 10 % Methane) Effective Area : 6000 cm² (@ 20 keV) Energy Resolution : ~10% FWHM at 22 keV Field of View : 1° x 1° FWHM (Collimator : 50µ Sn + 25µ Cu + 100µ Al ) Blocking shield on sides and bottom : 1mm Sn + 0.2 mm Cu Timing Accuracy : 10 μsec in time tagged mode (oven-controlled oscillator). Onboard purifier for the xenon gas G.C.Stewart Berlin

  8. LAXPC: Effective Area G.C.Stewart Berlin

  9. Large Area X-ray Proportional Counter (LAXPC) G.C.Stewart Berlin

  10. LAXPC: Collimator G.C.Stewart Berlin

  11. CZT Imager characteristics G.C.Stewart Berlin

  12. CZT-Imager with a coded mask (Qualification Model) G.C.Stewart Berlin

  13. CZT Detector 4 cm X 4 cm HV Connector Connectors CZT crystal Thermal conductor Thermal conductor ASIC G.C.Stewart Berlin

  14. SXT Characteristics Telescope Length: 2465 mm (Telescope + camera + baffle + door) Top Envelope Diameter: 386 mm Focal Length: 2000 mm Epoxy Replicated Gold Mirrors on Al substrates in conical Approximation to Wolter I geometry. Radius of mirrors: 65 - 130 mm; Reflector Length: 100 mm Reflector thickness: 0.2 mm (Al) + Epoxy (~50 microns) + gold (1400 Angstroms) Minimum reflector spacing: 0.5 mm No. of reflectors: 320 (40 per quadrant) Detector (Swift Heritage): E2V CCD-22 600 x 600 Field of view : 41.3 x 41.3 arcmin PSF: 3 – 4 arcmins Sensitivity(expected): few x 10-14 cgs (1 cps/mCrab) G.C.Stewart Berlin

  15. Soft X-ray Telescope G.C.Stewart Berlin

  16. Four Fe-55 calibration (corner) sources • One Fe 55 calibration door source • Optical Blocking Filter • CCD Assy. including TEC • PCB with front-end electronics G.C.Stewart Berlin

  17. SXT Engineering and Flight Models G.C.Stewart Berlin

  18. Astrosat SXT FM FPCA in Thermal Vacuum Chamber at Birmingham University G.C.Stewart Berlin

  19. G.C.Stewart Berlin

  20. CCD Performance Nominal • Noise ~6 – 10 e- • Resolution at Mn ~157 eV (Lab Electronics) G.C.Stewart Berlin

  21. SXT CCD (Eng.) Data with TIFR built Electronics Isolated pixels only 5.9 and 6.4 keV peaks Resolution ~140 eV Si escape peaks 3.70 and 4.15 keV G.C.Stewart Berlin

  22. Door and Corner X-ray Calibration Sources Optical LED Image G.C.Stewart Berlin

  23. SXT Effective Area vs. Energy (after subtraction of shadowing effects due to holding structure) G.C.Stewart Berlin

  24. Scanning Sky Monitor (SSM) • Detector : 3 x Proportional counters with resistive anodes • Ratio of signals on either ends of anode gives position. • Energy Range : 2 - 10 keV • Position resolution : 1.5 mm • Field of View : 10o x 90o (FWHM) • Sensitivity : 30 mCrab (5 min integration) • Time resolution : 1 ms • Angular resolution : ~ 10 arc min G.C.Stewart Berlin

  25. Status • Engineering Environmental Tests almost complete • Flight Model Construction Well Advanced (UVIT detectors and SXT CCD camera complete) • Spacecraft Assembly begun – most subsystems complete • Launcher Assigned • Launch Date G.C.Stewart Berlin

  26. ASTROSAT – Key Strengths Simultaneous V/UV to hard X-ray measurements LEO+ 70 inclinclination Low , stable? Background Large area at high X-ray energies UV imaging capability Low pile-up in CCD Fast Slewing ?? G.C.Stewart Berlin

  27. ASTROSAT – Key Projects AGN/Binaries: Simultaneous UV to hard X-ray timing/monitoring Galactic Novae: UV to X-ray Observations (TOO program) Magnetars: Multi-wave observations LMXBs: Persistent Pulsations and thermonuclear bursts Galactic Black Holes and micro / nano quasars Binary X-ray Pulsars: Cyclotron Resonance Scattering Features (X-ray Observations) Clusters of galaxies: X-ray & UV Observations G.C.Stewart Berlin

  28. ASTROSAT – Key Projects Supernova Remnants: X-ray and UV Observations UVIT observations of Star Forming galaxies, Young stellar objects, Galactic Structure, Proto- and Planetary Nebulae UV Extinction in the Galaxy (Archival Data) Miscellaneous: Study nano quasars and Compton thick sources, Observations of Stellar Flares, GLAST/INTEGRAL/BAT Sources, Surveys - multi wave, deep fields G.C.Stewart Berlin

  29. AGN (bright) • 4/5 decade SEDs - Resolving all the spectral components : UV and soft X-rays (thermal) from accretion disk, hard X-ray reflection component, intrinsic power-law component • Variability correlation and lags between UV, soft and hard X-rays • Variability correlation and lags between Fe-K line and Compton Reflection • Bright Compton thick G.C.Stewart Berlin

  30. H LAXPC C SXT CZTI Spectral model from Rephaeli et al. (1999) SXT: Clusters of galaxies 34 G.C.Stewart Berlin

  31. Binary X-ray Pulsars with Astrosat Simulated 10 ks observations of hard X-ray spectrum of Accreting Pulsar 4U 0115+63 The cyclotron lines are well resolved by ASTROSAT G.C.Stewart Berlin

  32. Time Allocation G.C.Stewart Berlin

  33. Coming Next Year ! G.C.Stewart Berlin

  34. Simultaneous UV to hard X-ray spectral measurements with ASTROSAT: Blazars, HPQs, OVVs etc. • Science Drivers: Jet Physics, particle injection and acceleration • Synchrotron X-ray emission from the highest energy e- • Electron/proton injection. • Acceleration and cooling related variability patterns in Sync. components of FSRQs and LBLs. • UV and soft X-ray variability can pin down the transition between the emission from slow and fast cooling e- and thus obtain estimates of magnetic field and Doppler factors of the jets. • Shocks in jets. Geom: viewing angle, jet opening angle. • Underlying Accretion disk in Blazars ? Can be revealed during minima when the beamed component is suppressed. G.C.Stewart Berlin

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