moriond 2001jordan goodmanmilagro collaboration the milagro gamma ray observatory the physics of...

Jordan Goodman Milagro Collaboration Moriond 2001

The Milagro Gamma Ray Observatory

• The Physics of Milagro• Milagrito

– Mrk 501– GRB 970417a

• Milagro– Description– Recent Results - Crab– Future Directions

Jordan Goodman

University of Maryland


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


Observing the High Energy Sky

10 9 10 11 10 10 10 1013 15 17 19

1 GeV 1 TeV 1 PeV 1 EeV

Satellites

Fly’s Eye / HiRes

Air Cherenkov

Milagro

EAS Arrays

Solar Arrays

Akeno /Auger

Milagro

•Water-Cherenkov Detector

•Threshold ~300 GeV

•Wide-angle

• /hadron Separation

•24 Hour – all year operation


Milagro Site

Located near Los Alamos, NM, USA

8650’ Elevation

60m X 80m X 8m covered pond


Milagro Site

Counting House

Pond Utility Building (PUB)

Office Trailer

Testing Trailer


Milagrito

A prototype for the full Milagro detector

Single layer of 230 PMTs with no muon detection

Milagrito operated at >250Hz from Feb 97 to April 98 (>85% livetime)

More than 9 billion events - 9 Terabytes

M ilagrito


Mrk 501 Flare


Milagrito Results – MRK 501


MRK 501


Milagrito - GRB 970417a

• Searching 54 Batse bursts (T90)

• One burst 970417a showed 18 events w/background of 3.46

• This has a prob< 2.9x10-8 • Accounting for all search

trials – combined accidental chance 1/150

• This could mean TeV emission from GRBs Batse 1 error

circle


Milagrito - GRB 970417a


Milagrito Moon Shadow


Milagro

Air Shower Layer

Hadron/Muon layer

2m

8" PMTs

Light-tight Cover

8 m

80m50m

450 Top Layer 8” PMTs

273 Bottom Layer 8” PMTs


Milagro Construction


Milagro


Angle Reconstruction

For large showers, the angle can be reconstructed to better than 0.50o. (However, there are systematics associated with core

location)


Events


Milagro Energy Response


Milagro Moon Shadow: Aug 2000 – Jan 2001

Nhit >150, Nfit > 20


Gamma / Hadron Separation in Milagro

Gammas (MC)

Data

Gammas (MC)


P


Crab Nebula


Crab Data


Crab Signal - Time Evolution


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)


Milagro Sensitivity to the Crab

Events per Day

No /had Separation

With /had Separation

Complete Milagro

Whipple 22.5 2.8 9.5

HEGRA 16.8 2.1 3.8 6.9

CAT 17.3 2.2 3.9 7.0

Tibet 49.8 6.2 11.1 21.0

Milagro Prelim.

~20 1.6 5.0


Outrigger array

• Adding ~150 tanks• Used for Core location

– Improved angle– Improved Energy

Reconstructed Energy in TeV

Energy Resolution

0.75 76%3.5 65%7 64%

11 45%


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


Lowering the trigger threshold


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%


Conclusions

• Milagro is now online

• We are seeing sources

• We are improving the detector

• We hope for many important Physics results soon!

moriond 2001jordan goodmanmilagro collaboration the milagro gamma ray observatory the physics of...

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