Gamma-ray Astronomy at Hanle B.S.Acharya

Tata Institute of Fundamental Research,

( [email protected]

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

IAO, Hanle Mt Abu KGF CRL, Ooty HEGRO, Pachmarhi

Latitude: 32 ° 46΄ 46˝ N Longitude : 78 ° 57΄ 51˝ E Altitude : 4300 m

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 Higher Cherenkov photon density at higher altitude Lower atmospheric attenuation of Cherenkov photons Lower energy threshold at higher altitudes Interesting physics issues: more sources can be observed, cutoffs in spectra of Active Galactic Nuclei, pulsars Overlapping observations with FERMI Phase 1: HAGAR (IIA+TIFR) 7 element WS array (non-imaging); Phase 2: Now operating 21 m Dia MACE (BARC) imaging Tel.

Coming soon, by 2012 Phase 3: MACE-II Stereo imaging; 2013+

High Altitude GAmma Ray (HAGAR) Telescope

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7 telescopes consisting of 7 para-axially mounted parabolic mirrors of diameter 0.9 m

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f/D ~ 1

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

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Tracking system : Alt-azimuth design

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High voltages to phototubes given through CAEN controller

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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

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

2005

First HAGAR Telescope at Hanle

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7 telescopes consisting of 7 para-axially mounted parabolic mirrors of diameter 0.9 m

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f/D ~ 1

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Front Coated 10mm thick glass mirrors

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Total mirror area ~ 30 m 2

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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 + NSB 1GHz sampling Telescope pulse

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

Shower front is fitted to plane front

Angular Resolution= 0.23 ± 0.09 degree

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.

γ e + /e hadrons μ + /μ Estimation of energy threshold and collection area Gamma-hadron separation (GHS) parameters * 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 : 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 × 10 4 m 2 5. Sensitivity : 1.3σ/√(hour) for Crab like sources

Saha et al. OG2.5 – 1129, ICRC

Sensitivity

HAGAR Observation Summary

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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

Calibration runs (Fixed angle runs) Dark region runs (Fake sources)

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

Results from HAGAR : Crab Nebula

Data analysis method :

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Estimation of space angle of each shower using plane front approximation

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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/cm 2 /s

Britto et al. OG2.5 - 943

Crab nebula :

Preliminary Results

Estimate of Crab flux from HAGAR is consistent with other experiments

Results from HAGAR : Crab and Geminga Pulsar

Crab pulsar

P = 33 ms

Geminga pulsar

P = 237 ms

Data stretch : 76 hours 49 hours 3σ upperlimit 1.5 10 -11 ph/cm 2 /s 3.6 10 -11 ph/cm 2 /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

Results from HAGAR : Mkn421

Flaring activity in February, 2010 HAGAR observation period : 13 – 20 February, 2010 Total duration : 479 Minutes

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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

Mrk421 Light Curves …

Object Mrk421 Mrk421 Observation Period

MJD 55200+

Exposure time (hr) Mean Gamma Ray Rate (per min) Error signific ance Feb. 2010 March –April 2010 7.98

9.9

13.4 4.9

1.05 12.7

0.97

5.05

13-19 Feb, 2010

EPOCH1 EPOCH3 EPOCH2 EPOCH4

Epoch Epoch 1 Epoch2 Doppler factor 20 26 Epoch3 Epoch4 Avg MAGIC 25 23 21 Magnetic field [G] 0.027

0.019

0.018

0.027

0.038

U_e [erg/cc] 0.9 x 10 -3 0.66 x 10 -3 0.6x 10 -3 0.9 x 10 -3 1.16 x 10 -3 Log E_min [eV] 9.2

8.7

9.6

9.0

8.6

Log E_max [eV] 12.1

12.1

12.2

12.1

13.6

E_break [eV] 11.3

11.45

11.5

11.5

11.3

P1 2.2

2.2

2.2

2.4

2.2

P2 4.6

4.0

4.0

4.3

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.

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The maximum flux above 250 GeV is found to be between 6 -7 Crab units.

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A very peculiar behaviour (SLOW RISE and FAST DECAY) of this flare is observed in Fermi LAT (2 - 300 GeV ) observation.

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Intra-night flux variations were seen by HAGAR and Fermi-LAT during the flare.

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A correlated variability in X-rays and gamma rays is seen, which strengthens the belief that gamma rays are produced via SSC in Mrk421.

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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

Phase II of HiGRO

21 m diameter basket Energy threshold 20-40 GeV Collection area – ~ few times 10

5

m

2  

356 (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 Size : 2.23 m x 2.14 m x x 1.327 m 4 deg Weight : 1200 kg

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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

MACE gamma-ray telescopes

21 m diameter basket Energy threshold 20-40 GeV

At Hanle :

Status of Work on MACE

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

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 FADC pulse shape 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

IIA, SINP, BARC, TIFR…

Thanks !

Pachmarhi, Madhya Pradesh