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Multi-TeV -r ay Astronomy with GRAPES-3

Pravata K Mohanty On behalf of the GRAPE-3 collaboration Tata Institute of Fundamental Research, Mumbai. Multi-TeV -r ay Astronomy with GRAPES-3 . Workshop on Astroparticle Physics , Bose Institute, Darjeeling, 10 - 12 December 2009. High energy -ray astronomy.

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Multi-TeV -r ay Astronomy with GRAPES-3

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  1. Pravata K Mohanty On behalf of the GRAPE-3 collaboration Tata Institute of Fundamental Research, Mumbai Multi-TeV -ray Astronomy with GRAPES-3 Workshop on Astroparticle Physics , Bose Institute, Darjeeling, 10 - 12 December 2009

  2. 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.

  3. 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 …..

  4. 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 s 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

  5. -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 s GRAPES-3 Field of View • 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 Many TeV sources in GRAPES-3 Field of View

  6. Duty Cycle of GRAPES-3 s Duty cycle (%)

  7. GRAPES-3 Angular Resolution Even – Odd Method s 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

  8. GRAPES-3 Angular Resolution Left – Right Method s Space angle -> Division of the array to left and right half through the line joining the core and the center of the shower.

  9. Moon Shadow Method s angle from moon center ----> (a) Ne > 103.2 , (b) Ne > 103.5 , (c) Ne > 103.75 , and (d) Ne > 104.0

  10. GRAPES-3 Angular Resolution Comparison of the 3 methods s Paper submitted to Astroparticle Physics, A Oshima et al.

  11. Muons in EAS Data s 20m 40m 60m 80m Detected Muons 

  12. CR Rejection Efficiency Data MC s

  13. Observation of CRAB Nebula On source region: ~2.7σ, after back ground rejection s Observation period: Mar 2000 –Sep 2004 Off source region ±8° in the direction of right ascension

  14. Diffuse -ray flux Upper Limit s GRAPES-3

  15. Enhancing the GRAPES-3 sensitivity Expanding of Muon Detector area s Aim: To increase the background rejection by doubling the muon detector areai.e. 560 m2 -> 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)

  16. Construction Plan for New Muon Detector Civil construction courtesy: Mr. B.S.Rao s 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

  17. 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 s

  18. 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

  19. Cosmic ray Rejection Efficiency Expanded Present

  20. -ray retention efficiency Present Expanded

  21. GRAPES-3 sensitivity to CRAB one year observation • 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) Expanded present

  22. 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

  23. THANKS

  24. 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

  25. 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 s

  26. Triggering Threshold < 10 TeV Duty Cycle: March 2000 - Sep 2004 s

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