The Milagro Gamma Ray Observatory

1. 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 Milagro Collaboration

2. 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 Milagro Collaboration

3. 1 G e V 1 T e V 1 P e V 1 E e V 19 9 1 1 1 3 1 5 1 7 1 0 1 0 1 0 1 0 1 0 1 0 Satellites Solar Arrays Air Cherenkov Milagro EAS Arrays Fly’s Eye / HiRes Akeno /Auger Observing the High Energy Sky • Milagro • Water-Cherenkov Detector • Threshold ~300 GeV • Wide-angle • g/hadron Separation • 24 Hour – all year operation Milagro Collaboration

4. Milagro Site Located near Los Alamos, NM, USA 8650’ Elevation 60m X 80m X 8m covered pond Milagro Collaboration

5. Pond Utility Building (PUB) Counting House Testing Trailer Office Trailer Milagro Site Milagro Collaboration

6. 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 Milagro Collaboration

7. Mrk 501 Flare Milagro Collaboration

8. Milagrito Results – MRK 501 Milagro Collaboration

9. MRK 501 Milagro Collaboration

10. 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 1s error circle Milagro Collaboration

11. Milagrito - GRB 970417a Milagro Collaboration

12. Milagrito Moon Shadow Milagro Collaboration

13. 8 m 50m 80m Milagro 450 Top Layer 8” PMTs 273 Bottom Layer 8” PMTs Milagro Collaboration

14. Milagro Construction Milagro Collaboration

15. Milagro Milagro Collaboration

16. Milagro Milagro Collaboration

17. Angle Reconstruction For large showers, the angle can be reconstructed to better than 0.50o.(However, there are systematics associated with core location) Milagro Collaboration

18. Events Milagro Collaboration

19. Milagro Energy Response Milagro Collaboration

20. Milagro Moon Shadow: Aug 2000 – Jan 2001 Nhit >150, Nfit > 20 Milagro Collaboration

21. Gammas (MC) Data Gammas (MC) Gamma / Hadron Separation in Milagro Milagro Collaboration

22. P g Milagro Collaboration

23. Crab Nebula Milagro Collaboration

24. Milagro Collaboration

25. Crab Data Milagro Collaboration

26. Crab Signal - Time Evolution Milagro Collaboration

27. Predicted Crab Signal in Milagro from ACTs 1Cantenese and Weeks (1998) 2Amenomori et al (1999) Milagro Collaboration

28. Milagro Sensitivity to the Crab Milagro Collaboration

29. Outrigger array • Adding ~150 tanks • Used for Core location • Improved angle • Improved Energy Milagro Collaboration

30. 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 Milagro Collaboration

31. Lowering the trigger threshold Milagro Collaboration

32. 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% Milagro Collaboration

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