Gamma-ray Astronomy at Hanle

B.S.AcharyaTata Institute of Fundamental Research,

(acharya@tifr.res.in)

6th WAPP, Dec 17-19, 2011, Darjeeling

IAO, Hanle

CRL, Ooty

KGF

HEGRO, Pachmarhi

Latitude: 32Latitude: 32°° 46 46΄ 46˝ N΄ 46˝ NLongitude : 78Longitude : 78° 57΄ 51˝ E° 57΄ 51˝ E

Altitude : 4300 mAltitude : 4300 m

Mt Abu

Ground-based Gamma-ray Astronomy at Hanle

A collaboration of Indian Institute of Astrophysics, Bangalore

Tata Institute of Fundamentral Research, MumbaiApS Division, BARC, Mumbai

SINP, Kolkata

High Energy Gamma-ray Astronomy

Gamma ray Astronomy : Atmospheric Gamma ray Astronomy : Atmospheric Cherenkov Cherenkov experiment at high altitude in the experiment at high altitude in the HimalayasHimalayas Higher Cherenkov photon Higher Cherenkov photon

density at higher altitudedensity at higher altitude

Lower atmosphericLower atmospheric attenuation of Cherenkovattenuation of Cherenkov photonsphotons

Lower energy threshold Lower energy threshold at higher altitudesat higher altitudes

Interesting physics issues:Interesting physics issues: more sources can be observed,more sources can be observed, cutoffs in spectra of Active Galacticcutoffs in spectra of Active Galactic Nuclei, pulsarsNuclei, pulsarsOverlapping observations with FERMI Overlapping observations with FERMI

Phase 1: HAGAR (IIA+TIFR) 7 element WS array (non-imaging);

Now operatingPhase 2: 21 m Dia MACE (BARC) imaging Tel. Coming soon, by 2012Phase 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 extensivelyat CREST

2004-05

First HAGAR Telescope at Hanle2005

7 telescopes consisting of 7 para-axially mounted parabolic mirrors of diameter 0.9 mf/D ~ 1Front Coated 10mm thick glass mirrors Total mirror area ~ 30 m2

Photonis UV sensitive phototube (XP2268B) at the focus of each mirror

HAGAR Telscope Array

Installation during 2005-2008

2008

HAGAR at Hanle

Data acquisition and Telescope control

Flash ADC (Auqiris)8 channel: 7 Tel + NSB1GHz sampling

Telescope pulse

Sum

of

7 P

MT

pu

lses

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

Angular Resolution= 0.23 ± 0.09 degree

Shower front is fittedto plane front

Expected Performance of Experimental setups

Simulations of extensive air showers using CORSIKA*

Charged particles in shower are tracked to observation level takinginto account their interactions, decayprobabilities etc.

Estimation of energy threshold andcollection area

Gamma-hadron separation (GHS)parameters

γ e+/e- μ+/μ-

hadrons * http://www-ik.fzk.de/corsika

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 × 104 m2

5. Sensitivity : 1.3σ/√(hour) for Crab like sources

200 GeV for vertical showersfor 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 128.6 127.5Geminga pulsar 79.1 50.0LSI +61 303 25.6 28.3MGRO 2019+37 16.4 15.3PSR007+73 2.4 2.8Fermi pulsars 33.3 9.0

Mkn 421 133.0 157.3Mkn 501 59.4 64.71ES2344+514 80.2 92.93C454.3 15.3 15.3M87 2.0 2.7

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)×10-10 ph/cm2/s

Britto et al. OG2.5 - 943

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. OG2.2 - 276

Data stretch : 76 hours 49 hours3σ upperlimit 1.5 10-11 ph/cm2/s 3.6 10-11 ph/cm2/s on flux

Crab pulsar

P = 33 ms

Geminga pulsar

P = 237 ms

Upper limits given for Fermi PSR J0357+3206 Detected pulsars : PSR J0633+0532 PSR J2055+2539

Results from HAGAR : Mkn421

Amit Shukla et al. OG2.3 – 977 @ 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 GeVSignificance : 12.7σ

Hint of correlated variability in various bands

MJD 55200+

Mrk421 Light Curves …

EPOCH

1

EPOCH

2

EPOCH

3

EPOCH

413-19 Feb, 201013-19 Feb, 2010

EPOCH1 EPOCH2

EPOCH3 EPOCH4

Epoch Doppler factor

Magnetic field [G]

U_e [erg/cc] Log E_min [eV]

Log E_max [eV] E_break [eV]

P1 P2

Epoch 1 20 0.027 0.9 x 10-3 9.2 12.1 11.3 2.2 4.6

Epoch2 26 0.019 0.66 x 10-3 8.7 12.1 11.45 2.2 4.0

Epoch3 25 0.018 0.6x 10-3 9.6 12.2 11.5 2.2 4.0

Epoch4 23 0.027 0.9 x 10-3 9.0 12.1 11.5 2.4 4.3

Avg MAGIC

21 0.038 1.16 x 10-3 8.6 13.6 11.3 2.2 4.7

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.

MACE gamma-ray telescopes

21 m diameter basketEnergy threshold 20-40 GeVCollection 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

Phase II of HiGRO

Koul et al. OG2.5 - 803

MACE gamma-ray telescopes21 m diameter basketEnergy threshold 20-40 GeV

Status of Work on MACEAt Hanle :

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

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