Gamma-ray Astronomy at Hanle

1. Gamma-ray Astronomy at Hanle B.S.Acharya Tata Institute of Fundamental Research, (acharya@tifr.res.in) 6th WAPP, Dec 17-19, 2011, Darjeeling

2. IAO, Hanle Mt Abu HEGRO, Pachmarhi KGF CRL, Ooty Latitude: 32° 46΄ 46˝ N Longitude : 78° 57΄ 51˝ E Altitude : 4300 m

3. A collaboration of Indian Institute of Astrophysics, Bangalore Tata Institute of Fundamentral Research, Mumbai ApS Division, BARC, Mumbai SINP, Kolkata Ground-based Gamma-ray Astronomy at Hanle High Energy Gamma-ray Astronomy

4. Gamma ray Astronomy : Atmospheric Cherenkov experiment at high altitude in the Himalayas Higher Cherenkov photon density at higher altitude Lower atmospheric attenuation of Cherenkov photons Lower energy threshold at higher altitudes Phase 1: HAGAR (IIA+TIFR) 7 element WS array (non-imaging); Now operating Phase 2: 21 m Dia MACE (BARC) imaging Tel. Coming soon, by 2012 Phase 3: MACE-II Stereoimaging; 2013+ Interesting physics issues: more sources can be observed, cutoffs in spectra of Active Galactic Nuclei, pulsars Overlapping observations with FERMI

5. High Altitude GAmma Ray (HAGAR) Telescope • 7 telescopes consisting of 7 • para-axially mounted parabolic • mirrors of diameter 0.9 m • f/D ~ 1 • Photonis UV sensitive • phototube (XP2268B) • at the focus of each mirror • Tracking system : Alt-azimuth design • High voltages to phototubes given through CAEN controller • Data Acquisition system : CAMAC based, interrupt driven Data recorded on coincidence of at least 4 telescope pulses Data : absolute arrival time of shower (s) given by RTC photon density (pulse height) at each mirror given by 12 bit QDC arrival time of shower at each mirror (0.25 ns) given by TDC

6. Two prototype telescopes by – Bouving Foress First telescope tested extensively at CREST 2004-05

7. 2005 First HAGAR Telescope at Hanle • 7 telescopes consisting of 7 para-axially mounted parabolic mirrors of diameter 0.9 m • f/D ~ 1 • Front Coated 10mm thick glass mirrors • Total mirror area ~ 30 m2 • Photonis UV sensitive phototube (XP2268B) at the focus of each mirror

8. HAGAR Telscope Array Installation during 2005-2008

9. 2008 HAGAR at Hanle

10. Data acquisition and Telescope control

11. Sum of 7 PMT pulses Flash ADC (Auqiris) 8 channel: 7 Tel + NSB 1GHz sampling Telescope pulse

12. Overall Pointing accuracy : (16± 9) arc min Kiran Gothe et al.,

13. Shower front is fitted to plane front Angular Resolution= 0.23 ± 0.09 degree

14. Expected Performance of Experimental setups Simulations of extensive air showers using CORSIKA* Charged particles in shower are tracked to observation level taking into account their interactions, decay probabilities etc. Estimation of energy threshold and collection area Gamma-hadron separation (GHS) parameters γ μ+/μ- e+/e- * http://www-ik.fzk.de/corsika hadrons

15. Detector Simulation Site and instrument related parameters Atmospheric attenuation of Cerenkov photons Reflectivity of mirrors Phototube response Attenuation of pulse in coaxial cables Discriminator thresholds Trigger generation criteria

16. Performance Parameters of HAGAR 1. Trigger rate : Protons 9.6 Hz, Alpha particles 3.6 Hz, Electrons 0.16 Hz Total trigger rate ~ 13.4 Hz 2. Energy threshold : 200 GeV for vertical showers for any 4/7 telescopes triggering 3. Expected gamma ray rate from Crab like sources = 6.6/min 4. Collection area = 3.2 × 104 m2 5. Sensitivity : 1.3σ/√(hour) for Crab like sources Saha et al. OG2.5 – 1129, ICRC

17. Sensitivity

18. HAGAR Observation Summary • Regular observational runs commenced in September, 2008 Source Duration (hours) Name ON OFF Crab nebula 128.6 127.5 Geminga pulsar 79.1 50.0 LSI +61 303 25.6 28.3 MGRO 2019+37 16.4 15.3 PSR007+73 2.4 2.8 Fermi pulsars 33.3 9.0 Mkn 421 133.0 157.3 Mkn 501 59.4 64.7 1ES2344+514 80.2 92.9 3C454.3 15.3 15.3 M87 2.0 2.7 Calibration runs (Fixed angle runs) Dark region runs (Fake sources)

20. Results from HAGAR : Crab Nebula • Data analysis method : • Estimation of space angle of each shower using plane front approximation • Comparison of ON-OFF space angle distributions Crab nebula detection at 7.8sigma in 10.4 hours for threshold energy of 275 GeV Average count rate = 5.1±0.5 gamma-rays/minute Crab nebula flux : (3.9±0.7)×10-10 ph/cm2/s Britto et al. OG2.5 - 943

21. Preliminary Results Crab nebula : Estimate of Crab flux from HAGAR is consistent with other experiments

22. Crab pulsar Geminga pulsar P = 33 ms P = 237 ms Results from HAGAR : Crab and Geminga Pulsar Data stretch : 76 hours 49 hours 3σ upperlimit 1.5 10-11 ph/cm2/s 3.6 10-11 ph/cm2/s on flux Upper limits given for Fermi PSR J0357+3206 Detected pulsars : PSR J0633+0532 PSR J2055+2539 Singh et al. OG2.2 - 276

23. Results from HAGAR : Mkn421 Flaring activity in February, 2010 HAGAR observation period : 13 – 20 February, 2010 Total duration : 479 Minutes  ray rate ~ 13.4 ± 1 /Minute above 250 GeV Significance : 12.7σ Hint of correlated variability in various bands Amit Shukla et al. OG2.3 – 977 @ ICRC, Beijing

24. Mrk421 Light Curves … MJD 55200+

25. 13-19 Feb, 2010 EPOCH1 EPOCH3 EPOCH4 EPOCH2

26. EPOCH2 EPOCH1 EPOCH3 EPOCH4

28. We have detected a VHE gamma ray flare from Mrk421 on 17 February 2010, at energies above 250 GeV with 5 sigma confidence, in less than 40 minutes of observation. • The maximum flux above 250 GeV is found to be between 6 -7 Crab units. • A very peculiar behaviour (SLOW RISE and FAST DECAY) of this flare is observed in Fermi LAT (2 - 300 GeV ) observation. • Intra-night flux variations were seen by HAGAR and Fermi-LAT during the flare. • A correlated variability in X-rays and gamma rays is seen, which strengthens the belief that gamma rays are produced via SSC in Mrk421. • A small change is observed in the magnetic field and Doppler factor with change of the state of the source from pre flare to post flare.

29. MACE gamma-ray telescopes Phase II of HiGRO 21 m diameter basket Energy threshold 20-40 GeV Collection area – ~ few times 105 m2 • 356 (1m x1m) diamond turned panels • total mirror area 337 m2 • Mechanical structure 170 tons, 45 m high, 25 m dia • Camera : 1088 pixels covering FOV 4x 4 deg • Size : 2.23 m x 2.14 m x 1.327 m • Weight : 1200 kg • Expected energy threshold 20-30 GeV • Sensitivity : 5sigma detection of Crab in few minutes • Installation of MACE at Hanle expected in 2012 • Science runs expected to commence in 2013 Koul et al. OG2.5 - 803

30. MACE gamma-ray telescopes 21 m diameter basket Energy threshold 20-40 GeV

31. Status of Work on MACE At Hanle :

32. Status of HAGAR • HAGAR array was operational in Sept 2008. • After few engineering runs regular observations were started since October 2008 • (Shutdown 3 months in 2008-09, 2 months 2009-10, • aiming for 0 months in 2010-11 onwards) • Upgrade/Modifications to various sub-systems of HAGAR were also undertaken in addition to data analysis • -These upgrades were partly planned & partly from feed back from data collected. • Instrument upgrade • Calibrations (NSB monitoring, Relative Time offsets…) • Software (DAQ & Telescope control) • Data analysis methods/procedure

33. FADC pulse shape Improvements in HAGAR Setup and Analysis 1. DAQ modifications : Reduction in coincidence window using programmable digital delays Reduction in energy threshold using trigger based on analog sum of telescope pulses 2. Data from FADC system : Parallel DAQ system consisting of Flash ADC (Acqiris model no. DC271A) with sampling rate of 1 GS/s GHS parameters based on a. Pulse shape b. Density fluctutations c. Timing jitter Software padding for balancing sky brightness in ON/OFF region 3. Integration of HAGAR with MACE

34. IIA, SINP, BARC, TIFR…

35. Pachmarhi, Madhya Pradesh Thanks !