multi-tev -ray astronomy with grapes-3 pravata k mohanty on behalf of the grape-3 collaboration...
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Multi-TeV -ray Astronomy with GRAPES-3
Pravata K Mohanty
On behalf of the GRAPE-3 collaborationTata Institute of Fundamental Research, Mumbai
Workshop on Astroparticle Physics , Bose Institute, Darjeeling, 10 - 12 December 2009
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 > 10 TeV is still unexplored.
High energy -ray astronomy with EAS arrays
EAS experiments ideal > 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 …..
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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Front view of two muon modules in a station
Trigger - by scintillation detectors - Rate ~ 30 Hz - Efficiency (90%): ~ 30 TeV for ~ 50 TeV for P
-ray Astronomy with GRAPES-3
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GRAPES-3 Location:76.7E, 11.4N, 2200m a.s.l
Advantage of location: Can view both northern and southern skies
Target:Observation of sources detected by
HESS and MILAGRO like HESS J1908+063 MGROJ1908+06
Search for extended sources
Search for diffuse -ray flux
GRAPES-3 Field of View
Many TeV sources in GRAPES-3 Field of View
The unique advantage of GRAPES-3 for - ray astronomy is its large area compact tracking muon detector for CR background rejection
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Duty Cycle of GRAPES-3 D
uty
cycl
e (%
)
GRAPES-3 Angular Resolution
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Even – Odd Method
Space angle ->
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
GRAPES-3 Angular Resolution
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Left – Right Method
Space angle ->
Division of the array to left and right half through the line joining the core and the center of the shower.
Moon Shadow Method
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angle from moon center ---->
(a) Ne > 103.2 , (b) Ne > 103.5 , (c) Ne > 103.75 , and (d) Ne > 104.0
GRAPES-3 Angular Resolution
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Comparison of the 3 methods
Paper submitted to
Astroparticle Physics,
A Oshima et al.
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Muons in EAS Data
20m
40m
60m
80m
Detected Muons
CR Rejection Efficiency
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DataMC
Observation of CRAB Nebula
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On source region:
~2.7σ, after back ground
rejection
Off source region ±8° in the direction
of right ascension
Observation period:
Mar 2000 –Sep 2004
Diffuse -ray flux Upper Limit
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GRAPES-3
Enhancing the GRAPES-3 sensitivity
sAim: To increase the background rejection by doubling the muon detector area i.e. 560 m2 -> 1120m2
Already planned for this
Expanding of Muon Detector area
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)
Construction Plan for New Muon Detector
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Civil construction
Layout of the modules Side view of one module
2.5 m height of soil
Difference from existing muon detector:
(1) Single hall for ease of working (2) soil as absorber to save cost and time
courtesy: Mr. B.S.Rao
Construction Plan for New Muon Detector
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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
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> 0
Total number of showers
-ray retaining efficiency:
= Showers with N = 0
Total number of showers
Cosmic ray Rejection Efficiency
Present
Expanded
-ray retention efficiency
Expanded
Present
GRAPES-3 sensitivity to CRAB
Statistical significance
A T F
= A T FCR (1-CR)
A -> core selection area
T->Observation time of Crab (4 hour/day)
F -> Integral -ray flux (30-1000TeV)
FCR -> Integral CR ray flux (50-1000TeV)
-> Solid angle of view (=2)
one year observation
present
Expanded
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
THANKS
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 > 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
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 < 10 TeV Duty Cycle: March 2000 - Sep 2004