Gamma-ray Astronomy at Hanle B.S.Acharya Tata Institute of Fundamental Research, 6th WAPP, Dec 17-19, 2011, Darjeeling

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

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

Gamma ray Astronomy : Atmospheric Cherenkov experiment at high altitude in the Himalayas experiment at high altitude in the Himalayas Higher Cherenkov photon density at higher altitude density at higher altitude Lower atmospheric attenuation of Cherenkov attenuation of Cherenkov photons photons Lower energy threshold Lower energy threshold at higher altitudes at higher altitudes Interesting physics issues: more sources can be observed, more sources can be observed, cutoffs in spectra of Active Galactic cutoffs in spectra of Active Galactic Nuclei, pulsars Nuclei, pulsars Overlapping observations with FERMI 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 Stereo imaging; 2013+

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

Two prototype telescopes by – Bouving Foress First telescope tested extensively at CREST

First HAGAR Telescope at Hanle 2005  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 m 2   Photonis UV sensitive phototube (XP2268B) at the focus of each mirror

HAGAR Telscope Array Installation during

2008 HAGAR at Hanle

Data acquisition and Telescope control

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

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

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

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 e + /e - μ+/μ-μ+/μ- hadrons *

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

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 : 3. Expected gamma ray rate from Crab like sources = 6.6/min 4. Collection area = 3.2 × 10 4 m 2 5. Sensitivity : 1.3σ/√(hour) for Crab like sources 200 GeV for vertical showers for any 4/7 telescopes triggering Saha et al. OG2.5 – 1129, ICRC

Sensitivity

HAGAR Observation Summary  Regular observational runs commenced in September, 2008 Source Duration (hours) Name ON OFF Crab nebula Geminga pulsar LSI MGRO PSR Fermi pulsars Mkn Mkn ES C M Calibration runs (Fixed angle runs) Dark region runs (Fake sources)

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) × ph/cm 2 /s Britto et al. OG

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

Results from HAGAR : Crab and Geminga Pulsar Singh et al. OG Data stretch : 76 hours 49 hours 3σ upperlimit ph/cm 2 /s ph/cm 2 /s on flux Crab pulsar P = 33 ms Geminga pulsar P = 237 ms Upper limits given for Fermi PSR J Detected pulsars : PSR J PSR J

Results from HAGAR : Mkn421 Amit Shukla et al. OG2.3 – ICRC, Beijing 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

MJD Mrk421 Light Curves …

EPOCH1 EPOCH2EPOCH3EPOCH Feb, Feb, 2010

EPOCH1 EPOCH2 EPOCH3 EPOCH4

EpochDoppler factor Magnetic field [G] U_e [erg/cc] Log E_min [eV] Log E_max [eV] E_break [eV] P1P2 Epoch x Epoch x Epoch x Epoch x Avg MAGIC x

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 ( 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.

MACE gamma-ray telescopes 21 m diameter basket Energy threshold GeV Collection area – ~ few times 10 5 m (1m x 1m) diamond turned panels total mirror area 337 m 2  Mechanical structure 170 tons, 45 m high, 25 m dia  Camera : 1088 pixels covering FOV 4 x 4 deg Size : 2.23 m x 2.14 m x m Weight : 1200 kg  Expected energy threshold GeV  Sensitivity : 5sigma detection of Crab in few minutes  Installation of MACE at Hanle expected in 2012 Science runs expected to commence in 2013 Phase II of HiGRO Koul et al. OG

MACE gamma-ray telescopes 21 m diameter basket Energy threshold GeV

Status of Work on MACE At Hanle :

Status of HAGAR HAGAR array was operational in Sept After few engineering runs regular observations were started since October 2008 (Shutdown 3 months in , 2 months , aiming for 0 months in 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

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 FADC pulse shape Improvements in HAGAR Setup and Analysis

IIA, SINP, BARC, TIFR…

Thanks ! Pachmarhi, Madhya Pradesh

Crab 36 Off-pulse (nebula) Synchrotron and Inverse Compton components ON-pulse (pulsar)

Gamma Electrons Protons Shower core distance (m) Density of photons (#/m 2 ) Lateral Distribution of Cherenkov Photons

MRK421

Few Results of Mrk421… Flux > 3 Crab Feb.

HAGAR, MACE and CTA CTA NORTH : Upshi / HANLE ???