Multi-TeV ?-ray Astronomy with GRAPES-3

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Multi-TeV ?-ray Astronomy with GRAPES-3

• Pravata K Mohanty
• On behalf of the GRAPE-3 collaboration
• Tata Institute of Fundamental Research, Mumbai

Workshop on Astroparticle Physics , Bose
Institute, Darjeeling, 10 - 12 December 2009
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High energy ?-ray astronomy

• Cosmic Ray origin a long standing problem
• Conventional method Energy spectrum and
  composition
• More direct method Detection of high energy
  ?-rays
• High energy ?-ray astronomy is emerging as a very
  exciting field of astronomy.
• The detection of a large numbers of galactic and
  extra-galactic sources in GeV - TeV energy range
  by the current generation of IACT experiments
  such as HESS, VERITAS, MAGIC and very recent
  results of Fermi-LAT space telescope completely
  changed the scenario and our perception of ?-ray
  universe.
• The region gt 10 TeV is still unexplored.

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High energy ?-ray astronomy with EAS arrays

• EAS experiments ideal gt 10 TeV
• Large effective area
• Large FOV
• - 100 duty cycle
• Drawbacks Poor angular resolution
• Ideal for extended sources, flaring sources and
  sky survey
• Present EAS experiments GRAPES-3, ARGO-YBJ,
  Tibet AS-gamma, MILAGRO
• Future experiments HAWC, Tibet AS MD,
  GRAPES-3 Expanded MD ..

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The GRAPES-3 Experiment

• Scintillation detectors
• - 400, 1m2 each
• - Inter-spacing 8 m
• - Particle density (ADC)
• - Timing (TDC)
• Muon detector
• - 35 m2 x 16 modules
• - 4 orthogonal layers of proportional
• counters to track muons
• - 1 GeV threshold

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Trigger - by scintillation detectors -
Rate 30 Hz - Efficiency (90) 30 TeV for
? 50 TeV
for P
Front view of two muon modules in a station
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?-ray Astronomy with GRAPES-3
The unique advantage of GRAPES-3 for ?-
ray astronomy is its large area compact tracking
muon detector for CR background rejection
GRAPES-3 Location 76.7E, 11.4N, 2200m a.s.l
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• Advantage of location
• Can view both northern
• and southern skies
• Target
• Observation of sources detected by HESS and
  MILAGRO like HESS J1908063 MGROJ190806
• Search for extended sources
• Search for diffuse ?-ray flux

GRAPES-3 Field of View
Many TeV sources in GRAPES-3 Field of View
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Duty Cycle of GRAPES-3
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Duty cycle ()
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GRAPES-3 Angular Resolution
Even Odd Method
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Space angle -gt
Division of the array to two overlapping
sub arrays with odd and even numbered detectors
and determine the angle by each sub array
The systematic errors may be common to both and
will cancel out by the difference
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GRAPES-3 Angular Resolution
Left Right Method
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Space angle -gt
Division of the array to left and right
half through the line joining the core and the
center of the shower.
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Moon Shadow Method
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angle from moon center ----gt
(a) Ne gt 103.2 , (b) Ne gt 103.5 , (c) Ne gt 103.75
, and (d) Ne gt 104.0
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GRAPES-3 Angular Resolution
Comparison of the 3 methods
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Paper submitted to Astroparticle Physics, A
Oshima et al.
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Muons in EAS Data
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20m 40m 60m 80m
Detected Muons ?
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CR Rejection Efficiency
Data
MC
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Observation of CRAB Nebula
On source region 2.7s, after back ground
rejection
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Observation period Mar 2000 Sep 2004
Off source region 8 in the direction of right
ascension
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Diffuse ?-ray flux Upper Limit
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GRAPES-3
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Enhancing the GRAPES-3 sensitivity
Expanding of Muon Detector area
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Aim To increase the background rejection by
doubling the muon detector area i.e. 560 m2 -gt
1120m2 Already planned
for this
Increasing the density of
scintillation detectors
Aim To reduce the triggering threshold
energy (Simulation shows 8m to 4m
detector separation reduces threshold from 30TeV
to 15 TeV at 90 trigger efficiency. More
simulation required to conclude)
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Construction Plan for New Muon Detector
Civil construction
courtesy Mr. B.S.Rao
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2.5 m height of soil
Side view of one module
Layout of the modules
Difference from existing muon detector (1)
Single hall for ease of working (2) soil as
absorber to save cost and time
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Construction Plan for New Muon Detector
Detector 4000 proportional
counters exists from the KGF experiment will be
used to make 16 modules But all of them
to be remade. The major operation required are
cleaning, evacuation, filling gas and testing.
Design and procurement of necessary
equipments for this work already began.
Electronics DAQ logic would be same.
More compact design using latest
electronics like FPGA Optimistic
time frame for completion 2 years
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Simulation for Expanded Muon Detector

• CORSIKA QGSJET1 (Version 6.72)
• ?-ray showers 30-1000TeV
• proton showers 50-1000TeV
• CR rejection efficiency
• ?CR Showers with N?gt 0
• Total number of
  showers
• ?-ray retaining efficiency
• ?? Showers with N? 0
• Total number of showers

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Cosmic ray Rejection Efficiency
Expanded
Present
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?-ray retention efficiency
Present
Expanded
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GRAPES-3 sensitivity to CRAB
one year observation

• Statistical significance
• A T F? ? ?
• ? ? A T FCR ? (1-?CR)
• A -gt core selection area
• T-gtObservation time of Crab (4 hour/day)
• F? -gt Integral ?-ray flux (30-1000TeV)
• FCR -gt Integral CR ray flux (50-1000TeV)
• ?-gt Solid angle of view (??2)

Expanded
present
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Summary

• More efficient background rejection and higher
  sensitivity with expanded muon detector
• Enhanced potential for detection of new sources
  in the multi-TeV region with expanded muon
  detector

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THANKS
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Sensitivity

• Sensitivity depends on gamma ray flux from
  source, effective collection area and efficiency
  of charged cosmic ray background rejection
• Gamma ray flux extremely low gt 10 TeV. Not in
  our control
• Sensitivity can be increased by
• Increasing collection area
• Rejecting large fraction of cosmic ray background
• High background rejection
• High angular resolution, not much can be done in
  EAS experiments as the limit comes due to shower
  fluctuation
• Gamma hadron discrimination through muon content

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The GRAPES-3 Experiment

• Scintillator detectors 400, 1m2 each with 8m
  inter-detector separation
• Measures particle densities and relative arrival
  times
• to estimate primary energy and direction
• Muon detector 16 modules, 560 m2 area consists of
  3712 proportional counters

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Triggering Threshold lt 10 TeV
Duty Cycle March 2000 - Sep 2004
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