1. Gamma Ray Astronomy Initiatives in India
V.C.Sahni
Bhabha Atomic Research Centre
Mumbai, India

2. Gamma Ray Astronomy – Relatively young field # Direct detection upto ~10GeV outside atmosphere # Ground based detection uses atmosphere as transducer * Atmospheric Cerenkov Technique *Atmospheric Scintillation Technique
Multiple Probes are needed for getting a more accurate perspective of the multi-colour universe around us.

3. #Various available windows Radio, IR, Visible, X-Rays, Gamma Rays Gamma Rays – HE 30MeV-30GeV VHE 30GeV- 100TeV UHE >100TeV
#Why Gamma Ray Astronomy ?
*Possible sites of cosmic ray production
*Excellent probes of very energetic phenomena
Charge neutrality
*Understand new phenomena not seen at other energies
*Probes of intergalactic radiation fields

4. VHE gamma ray astronomy programmes in India
VHE gamma ray astronomy programmes in India * NRL-HARL Division of BARC Imaging Technique (TACTIC telescope at Mt. Abu(1400m amsl), Rajasthan) (ACT – first generation gamma ray telescope set up at Gulmarg(2700m amsl) in 1985) * HEG of TIFR Wavefront sampling Technique (PACT telescope at Pachmari, MP) * BARC, TIFR & IIA at Hanle (4200m amsl) - proposed 21m diameter MACE and 7 detector array HAGAR .

5. BARC VHE Gamma Ray Astronomy Programme
Set up high sensitivity telescope systems at
Mt. Abu & Hanle for probing the sky in the
GeV –TeV energy range.
Most recent window to the universe
(First detection of CRAB nebula in TeV energy
range in 1989 by the Whipple group)
TACTIC (1.0 TeV-50 TeV)
MYSTIQUE (10 TeV-500 TeV)
(wide angle survey instrument)
MACE (30 GeV-30 TeV)
(at 4200m altitude at Hanle,Ladakh)

6. CRAB Nebula – Cosmic Laboratory.

7. Gamma Ray Sky as seen by EGRET (1991-2000)
Earlier Satellite Experiments
OSO 1967, SAS2 1972, COSB 1975

8. Challenges in Ground based VHE gamma-ray Astronomy
Extremely weak flux (1 photon/sq.m/week in space)
Large CR background (>500:1)
Large LONS background
Low duty cycle (<15%)
Variability of the transducer (atmosphere)
Advantages of Atmospheric Cerenkov Technique
Large effective area (~10**4 sq. m)
Good angular resolution (2nd gen. Systems)
Calorimetric component

9. Sensitivity enhancement
CRAB Nebula Flux [F(0.5TeV) ~4.5X10**-11/sqcm/s]
ON/OFF monitoring [10 hr observation ~0.7sigma]
Imaging [10 hr observation ~8.1 sigma]
Fg~70% acceptance
Fp~99.7% rejection
Stereo imaging
Spectral content
Temporal characteristics
Polarization index

10. Atmospheric Cerenkov Technique--

11. Physics behind Cerenkov Imaging Technique

12. Comparison of actual recorded images

14. TACTIC Telescope TeV Atmospheric Cerenkov Telescope with Imaging Camera
349-pixel camera
0.3deg resolution
9.5sq.m light collector
Energy threshold ~1 TeV

15. Point Spread Function of the TIE Light Collector

16. TIE Drive Control System (Alt.-Az. Mounting)

17. Block Diagram of the TIE DAS

18. TACTIC Data Acquisition System

19. TACTIC Control Console.

20. Sensitivity estimate of TACTIC

21. Mkn-501 Observations with prototype 81-pixel camera

22. Crab Nebula Observations

23. Crab Nebula Observations

24. .

25. .

26. Mkn421 Observations

27. Mkn421 Observations

28. Simulation results

29. Simulation results

30. TACTIC results

31. TACTIC Vertex Elements
Additional discrimination parameters
Polarization
Spectral content
Temporal characteristics
Duplex camera design
Beam splitters
Dichroic filters
Polarizers
High speed digitizers

32. 4-element TACTIC array .

33. TACTIC Important Publications
Semi-intelligent trigger-generation scheme for Cerenkov light Imaging cameras. C.L. Bhat, A.K.Tickoo, R.Koul and I.K.Kaul Nucl. Inst. & Methods A, 340 (1994) 413.
A computer-programmable delay-generator scheme for TACTIC gamma-ray telescope. A.K.Tickoo, C.L.Bhat, R.Koul, I.K.Kaul, S.K.Kaul and S.R.Kaul Nucl. Instr. & Methods A, 349 (1994) 600.
Hybrid Zener based VDN – a better choice for Cerenkov light imaging camera. C.L.Bhat, R.Koul, S.R.Kaul, S.K.Kaul, I.K.Kaul & H. Goyal Meas. Sci. Technol
Use of ‘look-up’ table improves the accuracy of a low-cost resolver-based absolute shaft encoder. S.K.Kaul, R.Koul, C.L.Bhat, I.K.Kaul and A.K.Tickoo Meas. Sci. Technol.,
Potential of TACTIC for cosmic ray mass composition investigations. R.C. Rannot, C.L.Bhat, M.L.Sapru, A.K.Razdan, V.N.Gandhi, T.Thouw, H. Rebel and D. Heck. Nucl. Phys. B (Proc. Suppl.) 52B (1997) 269.
Very high Energy gamma-rays from Markarian 501.R.J.Protheroe, C.L.Bhat, P. Fleury, E.Lorentz, M. Teshima & T.C.WeekesProc. 25th ICRC, 8, 1997, 317.
AGN detection ranges of MACE and TACTIC Imaging gamma-ray telescopes. C.L.Kaul, K.Shanthi, C.L.Bhat, A.K.Tickoo & R.K.Kaul Experimental Astronomy, 9, 1999, 81.
Drive control system for the TACTIC gamma-ray telescope A.K.Tickoo, R.Koul, S.K.Kaul, I.K.Kaul, C.L.Bhat, N.G.Bhatt, M. Kothari, H.C.Goyal, N.K.Agarwal & S.R.Kaul Experimental Astronomy, 9, 1999, 81.
First results on characterization of Cerenkov images through combined use of Hillas fractal and wavelet parameters.A.Haungs, A.K.Razdan, C.L.Bhat, R.C.Rannot and H.Rebel Astropart. Phys. 12, 1999, 145.
Artificial Neural Network approach for reconstruction of event arrival direction in wide-angle atmospheric Cerenkov detector arrays : A feasibility study.V.K.Dhar, A.K.Tickoo, R.Koul and C.L.BhatExperimental Astronomy, 10, 2000,487

34. TACTIC Important Publications
On single counts rate stabilization scheme employed in Imaging camera of TACTIC gamma-ray telescope. N.Bhatt, K.K.Yadav, A. Kanda, R. Koul, S.R.Kaul, H.C.Goyal, V.K.Dhar, S.K.Kaul, K.Venugopal, A.K.Tickoo, I.K.Kaul, M.Kothari and C.L.Bhat Meas. Sci. Technol., 12, 2001, 167.
TACTIC Imaging gamma-ray telescope : A simulation study of the effect of switched of pixels on its quality factor. S.K.Charagi, M.K.Koul, M.L.Sapru, R.C.Rannot & C.L.Bhat Experimental Astronomy, 11, 2001, 71.
Examining feasibility of air shower core-location from polarization state of associated Cerenkov light. V.J.Gokhale, R.C.Rannot, A.K.Tickoo, S.Bhattacharyya and C.L.Bhat Experimental Astronomy, 12, 2001, 195.
Image and non-image parameters of atmospheric Cherenkov events : a comparative study of their -ray/hadron classification potential in ultrahigh energy regime. A.Razdan, A. Haungs, H. Rebel and C.L. Bhat Astroparticle Physics 17 (2002)
Programmable topological trigger generator for the 349-pixel imaging camera of the TACTIC telescope. S.R.Kaul, R.Koul, I.K.Kaul, A.K.Tickoo, K.K.Yadav and C.L.Bhat Nucl. Instr. & Methods A, 496, 2003, 400.
Real time data acquisition and control system for the 349-pixel TACTIC atmospheric Cerenkov imaging telescope;K.K.Yadav, R.Koul, A.Kanda, S.R.Kaul, A.K.Tickoo, R.C.Rannot, P.Chandra, N.Bhatt, N.Chouhan, K.Venugopal, M.Kothari, H.C.Goyal, V.K.Dhar and S.K.Kaul; Nucl. Instr & Methods A 527,2004,

35. PACT (Pachmari Array of Cerenkov Telescopes)
PACT (Pachmari Array of Cerenkov Telescopes) *Temporal and spatial distribution of Cerenkov photons for g/p segregation. *Arrival time recorded .

36. PACT Layout
Each telescope 7 mirrors of 0.9m dia
25 telescopes deployed
FoV ~ 3 deg
4 sectors
4-fold coincidence
Timing and pulse height data recorded

37. PACT Results
# Pulsed emission from TeV sources detected from CRAB Pulsar and Geminga (not confirmed yet by other telescopes)
Once confirmed this result will have far reaching consequences in Astrophysics

38. Concurrent observation campaigns (PACT, TACTIC & Optical telescopes in India) * Mkn421, Mkn501, H1426 * Concurrent detection of short duration flares with telescopes using different techniques for g/p segregation.

39. Why GeV Astronomy ?
# Only a handful of TeV sources detected
# EGRET detected 270 sources in MeV-GeV range
# >100 sources expected in the GeV range

40. GeV Astronomy - Need for a large light collector.

41. Increase in Cerenkov photon flux at high altitude

42. MACE telescope .

45. MACE sensitivity

46. Mkn 421 Energy Spectrum .

47. Thank you