The Milagro Gamma Ray Observatory

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The Milagro Gamma Ray Observatory
Jordan Goodman University of Maryland

• The Physics of Milagro
• Milagrito
• Mrk 501
• GRB 970417a
• Milagro
• Description
• Recent Results - Crab
• Future Directions

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The Physics of Milagro

• The Sources of VHE/UHE Cosmic Rays
• Crab
• Super Nova Remnants
• Active Galactic Nuclei
• High variability
• Gamma Ray Bursts
• High energies
• Absorption of TeV Photons
• Primordial Black Holes
• Solar Physics

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Observing the High Energy Sky

• Milagro
• Water-Cherenkov Detector
• Threshold 300 GeV
• Wide-angle
• g/hadron Separation
• 24 Hour all year operation

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Milagro Site
Located near Los Alamos, NM, USA 8650
Elevation 60m X 80m X 8m covered pond
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Milagro Site
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Milagrito

• A prototype for the full Milagro detector
• Single layer of 230 PMTs with no muon detection
• Milagrito operated at gt250Hz from Feb 97 to April
  98 (gt85 livetime)
• More than 9 billion events - 9 Terabytes

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Mrk 501 Flare
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Milagrito Results MRK 501
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MRK 501
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Milagrito - GRB 970417a

• Searching 54 Batse bursts (T90)
• One burst 970417a showed 18 events w/background
  of 3.46
• This has a problt 2.9x10-8
• Accounting for all search trials combined
  accidental chance 1/150
• This could mean TeV emission from GRBs

Batse 1s error circle
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Milagrito - GRB 970417a
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Milagrito Moon Shadow
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Milagro
450 Top Layer 8 PMTs
273 Bottom Layer 8 PMTs
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Milagro Construction
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Milagro
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Milagro
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Angle Reconstruction
For large showers, the angle can be reconstructed
to better than 0.50o. (However, there are
systematics associated with core location)
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Events
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Milagro Energy Response
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Milagro Moon Shadow Aug 2000 Jan 2001
Nhit gt 150, Nfit gt 20
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Gamma / Hadron Separation in Milagro
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P
g
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Crab Nebula
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(No Transcript)
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Crab Data
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Crab Signal - Time Evolution
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Predicted Crab Signal in Milagro from ACTs
Events per Day in Milagro Flux F(E) x (10-7/s/m2/TeV)
Whipple1 22.5 3.2 0.70 x E(TeV)-(2.49 0.08)
HEGRA1 16.8 2.7 0.82 x E(TeV)-(2.61 0.12)
CAT1 17.3 2.7 0.43 x E(TeV)-(2.57 0.16)
Tibet2 49.8 8.2 1.6 x E(TeV)-(2.62 0.17)
1 Cantenese and Weeks (1998) 2 Amenomori et al
(1999)
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Milagro Sensitivity to the Crab
Events per Day No g/had Separation With g/had Separation Complete Milagro
Whipple 22.5 2.8s 5.0s 9.5s
HEGRA 16.8 2.1s 3.8s 6.9s
CAT 17.3 2.2s 3.9s 7.0s
Tibet 49.8 6.2s 11.1s 21.0s
Milagro Prelim. 20 1.6s 5.0s
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Outrigger array

• Adding 150 tanks
• Used for Core location
• Improved angle
• Improved Energy

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Future Plans

• Complete Outriggers
• 34 are now online
• Put burst/GRB analysis online
• GRB alerts to network
• New trigger processor to lower threshold
• Discriminate against muon triggers
• Lower energy threshold
• Increase reach for GRB and other studies
• Improve Gamma / Hadron Separation
• Improve Angle Reconstruction

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Lowering the trigger threshold
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Risetime Trigger Processor
Data Gives At 27PMT threshold Raw Trigger Rate
14.5 kHz Not Fit (Muon Rate) 9 kHz Simulation
Predicts (Preliminary) Making a 100ns risetime
cut Total Trigger rate 2.6kHz Not Fit(Muon
Rate) 0.5kHz Gamma Efficiency 66 Proton
Efficiency 40
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Conclusions

• Milagro is now online
• We are seeing sources
• We are improving the detector
• We hope for many important Physics results soon!