1. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Milagro: A Synoptic VHE Gamma-Ray Telescope Gus Sinnis Los Alamos National Laboratory

2. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Why A Synoptic Telescope? Complete unbiased sky survey Transient phenomena –Gamma ray bursts –Flares from active galaxies –Solar events (coronal mass ejections) Year-round observation of all sources Extended sources –Diffuse emission from the Galactic plane cosmic ray generation and propagation –Molecular clouds –?? Discovery potential Prototyping of radically new technique

3. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Detectors in Gamma-Ray Astrophysics High Sensitivity HESS, MAGIC, CANGAROO, VERITAS Large Aperture/High Duty Cycle Milagro, Tibet, ARGO, HAWC? Low Energy Threshold EGRET/GLAST Large Effective Area Excellent Background Rejection (>99%) Low Duty Cycle/Small Aperture Space-based (small area) “Background Free” Large Duty Cycle/Large Aperture Moderate Area/Large Area (HAWC) Good Background Rejection Large Duty Cycle/Large Aperture High Resolution Energy Spectra Studies of known sources Surveys of limited regions of sky Sky Survey (<10 GeV) AGN Physics Transients (GRBs) <100 GeV Unbiased Sky Survey Extended sources Transients (GRB’s) Solar physics/space weather

4. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Milagro 2600m asl Water Cherenkov Detector 898 detectors –450(t)/273(b) in pond –175 water tanks 3.4x10 4 m 2 (phys. area) 1700 Hz trigger rate 0.5 o resolution 90% proton rejection 10 m

5. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 The Central Detector

6. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Background Rejection in Milagro Protons Gammas Gamma MC Data Proton MC Retain 50%  and 9% protons Not angular resolution – inherent rejection

7. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Effective Areas

8. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Energy Resolution Two new techniques –Direct event-by-event method –Spectral measurement compactness distribution of event excess S/B increases with energy (S/N ~ constant) –With a small significance we can measure spectra Replace with Crab spectrum plot

9. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Gamma-Ray Bursts Milagrito (Milagro prototype) Operated April 1997-1998 BATSE detected 54 GRBs within Milagrito’s field of view We scan the region around the BATSE position for an excess GRB 970417a had a post-trial probability of 1.7x10 -3

10. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Gamma-Ray Bursts I need some slides from David Noyes and Pablo here

11. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Sky Survey Milagro sky map ApJ 2004, 608, p680

12. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Extended Sources  Sensitivity to an extended source is relatively better for an EAS than an ACT because angular resolution is not as important  Sensitivity determined by –inherent proton rejection –observation time –effective area Not Detected (both) Detected (both) Detected Milagro only Milagro Whipple Courtesy: David Kieda ACT VII, Paris 2005

13. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Extended Sources – Galactic Plane  Cosmic rays interacting with matter in Galaxy produce p’s that decay into g rays  Gamma ray spectrum is sensitive to cosmic ray source models –inverse Compton component –point sources  EGRET observations up to 20 GeV indicated an excess > 1 GeV  Higher energy observations have proven elusive despite 20 years of effort  Milagro has made the first detection of TeV gamma rays from the Galactic plane  S/B level ~3x10 -4  Flux(>1 TeV) = 5.1x10 -10 cm -2 sec -1 sr -1  Spectral Index = -2.61 ± 0.07 (combined EGRET-Milagro fit) EGRET data

14. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Galactic Plane Milagro data 5x5 degree bins Significance Crab

15. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Galactic Plane E -2.51±0.05  Demonstrates the strength of EAS in finding diffuse and extended sources –Due to good “inherent” background rejection –Angular resolution unimportant –Large observation time –Large field of view  Milagro flux measurement is ~1/10 of previous upper limits

16. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Extended Sources  Search northern sky for large sources  ~6 degree source in Cygnus arm of Galaxy –EGRET observed as brightest region in Northern hemisphere  ~3 degree source near the Crab Nebula –coincident with an EGRET unID Tibet hotspot Milagro point source hotspot

17. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Solar Physics  Coronal mass ejections are an ideal laboratory to study particle acceleration in the cosmos  By monitoring the singles rates in all PMTs we are sensitive to “low”-energy particles (>10 GeV)  Milagro has detected 4 events from the Sun with >10 GeV particles

18. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 X7-Class flare Jan. 20, 2005  GOES proton data –>10 MeV –>50 MeV –>100 MeV  Milagro scaler data –> 10 GeV protons –~1 min rise-time –~5 min duration

19. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Future Instruments: ARGO-YBJ

20. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Farther Future:HAWC  Build pond at extreme altitude (Tibet 4300m or Chile 5200m)  Incorporate new design –Optical isolation between PMTs –Larger PMT spacing –Deeper PMT depth (in top layer) e   300 meters 4 meters ~$20M for complete detector ~60x sensitivity of Milagro – instantaneous sensitivity of Whipple over 2 sr Crab Nebula in 30 minutes (now 1 year) GRBs to redshift of >1 (now 0.4)

21. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Effective Areas: Future Detectors

22. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Survey Sensitivity

23. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 HAWC: Simulated Sky Map  C&G AGN  Hartmann IR model  known TeV sources  Milagro extended sources  1-year observation

24. Milagro Gus Sinnis Milagro NSF Review July 18-19, 2005 Conclusions  Milagro has met or exceeded all of its design goals  We have made exciting discoveries  First convincing detection of a TeV gamma ray source with a synoptic instrument  Complete survey of Northern sky  Diffuse emission from the Galactic plane  Extended sources of TeV gamma rays  Possible TeV emission from GRB  Clear demonstration of low-energy (5 GeV) capability for solar physics  We have pioneered a radically new technique