1. Gus Sinnis HAWC Review December 2007 Milagro a TeV Gamma-Ray Observatory Gus Sinnis Los Alamos National Laboratory

2. Gus Sinnis HAWC Review December 2007 Milagro: A Summary of Results 1991 Milagro proposal submitted to NSF & DOE –Funding started in 1994 (ended in 1998 for central reservoir) 1997 (Milagrito) Evidence for TeV emission from a gamma-ray burst (3  ) 1997 (Milagrito) Detection of Mrk 501 2000 Milagro begins physics operation 2002 Detection of Crab Nebula 2003 Detection of Mrk 421 2004 Outriggers installed (funding from 2002-2004) 2005 Discovery of Galactic diffuse emission 2007 Discovery of TeV emission from Cygnus 2007 Galactic Survey: 3 new sources 4 candidates 2007 Cosmic-ray anisotropy: anomalous spectrum

3. Gus Sinnis HAWC Review December 2007 Complementarity of TeV Gamma-Ray Detectors Imaging Air Cherenkov TelescopesExtensive Air Shower Arrays Energy Range.05-50 TeV Area > 10 4 m 2 Background Rejection > 99% Angular Resolution 0.05 o Energy Resolution ~15% Aperture 0.003 sr Duty Cycle 10% Energy Range 0.1-100 TeV Area > 10 4 m 2 Background Rejection > 95% Angular Resolution 0.3 o - 0.7 o Energy Resolution ~50% Aperture > 2 sr Duty Cycle > 90% High Resolution Energy Spectra Precision Study of Known Sources Source Location & Morphology Deep Surveys of Limited Regions of Sky Unbiased Complete Sky Survey Extended Sources Transient Objects (GRB’s & AGN) Multi-Wavelength/Messenger Observations

4. Gus Sinnis HAWC Review December 2007 Current Generation EAS Arrays Tibet AS  Milagro

5. Gus Sinnis HAWC Review December 2007

6. Gus Sinnis HAWC Review December 2007

7. Gus Sinnis HAWC Review December 2007 25 Northern Hemisphere Sources Whipple 4 (1969 - 2006) HEGRA 4 (1992 - 2002) Milagro 4 (+3 * ) (2000 - present) HESS6 (2004 - present) MAGIC 7 (2005 - present) VERITAS (coming soon!)

8. Gus Sinnis HAWC Review December 2007 Milagro 8 meters e  80 meters 50 meters Water Cherenkov Detector 2600m asl 898 detectors – 450(t)/273(b) in pond – 175 water tanks 4000 m 2 / 4.0x10 4 m 2 2-12 TeV median energy 1700 Hz trigger rate 0.5 o -1.4 o resolution 95% background rejection

9. Gus Sinnis HAWC Review December 2007 Event Reconstruction Measure time to <1 ns Direction reconstruction 0.5 o to 1.4 o (size dependent) Time (ns)

10. Gus Sinnis HAWC Review December 2007 Background Rejection in Milagro Proton MC Data  MC Hadronic showers contain penetrating component:  ’s & hadrons – Cosmic-ray showers lead to clumpier bottom layer hit distributions – Gamma-ray showers give smooth hit distributions

11. Gus Sinnis HAWC Review December 2007 Background Rejection (Cont’d) mxPE:maximum # PEs in bottom layer PMT fTop:fraction of hit PMTs in Top layer fOut:fraction of hit PMTs in Outriggers nFit:# PMTs used in the angle reconstruction Apply a cut on A 4 to reject hadrons: A 4 > 3 rejects 99% of Hadrons retains 18% of Gammas S/B increases with increasing A 4 Background Rejection Parameter

12. Gus Sinnis HAWC Review December 2007 Distribution of Excesses in the Galactic Plane cut level Crab Nebula Mrk 421 6.5 year data set (July 2000-January 2007) Weighted analysis using A4 parameter Crab nebula 15  Galactic plane clearly visible Cygnus Region

13. Gus Sinnis HAWC Review December 2007 Milagro has discovered 3 new sources & 4 candidate sources in the Galaxy. 5/7 of these TeV sources have GeV counterparts (only 13 GeV counterparts in this region - excluding Crab) Probability = 3x10 -6 Abdo, et al. ApJ 2007 C3 J0634+17 Geminga 108 106 C4 J2226+60EGRET E. Ona-Wilhelmi, et al., ICRC 2007 MGRO 1908+06

14. Gus Sinnis HAWC Review December 2007 H.E.S.S. A&A 2006  ~-2.0 E c ~20 TeV The Highest Energy Gamma Rays: HESS RX J1713.7-3946 HESS Observations 3 years of data 2003-2005 4.8  above 30 TeV

15. Gus Sinnis HAWC Review December 2007 Milagro detection with median energy of 90 TeV. Strong indicator of proton acceleration in this source. 1908+06 The Highest Energy Gamma Rays Preliminary Milagro data 6.4 x 10 -11 E -2.05 20 TeV cutoff 7.6  @ 90 TeV 6090 MGRO 1908+06

16. Gus Sinnis HAWC Review December 2007 The Cygnus Region C1 J2044+36 C2 J2031+33 MGRO J2031+41 MGRO J2019+37 MGRO J2019+37: 10.9σ –Extended source 1.1 o ± 0.5 o (top hat dia.) –Possible Counterparts GeV J2020+3658, PWN G75.2+0.1 MGRO J2031+41: 6.9σ (5.0σ post-trials) –Possible Counterparts: 3EG J2033+4118, GEV J2035+4214 TEV J2032+413 (⅓ of Milagro flux) –3.0 o ± 0.9 o (top hat dia.) C1 J2044+36: 5.5σ pre-trials –no counterparts –< 2.0 o C2 J2031+33: 5.3σ pre-trials –no counterparts –possible extension of MGRO J2019+37 –possible fluctuation of MGRO J2019 tail & diffuse emission & background Tibet AS  preliminary detections of 3 sources 5.8  4.5  3.8  Abdo, et al. ApJ 2007 Wang, et al. ICRC 2007

17. Gus Sinnis HAWC Review December 2007 TeV Galactic Diffuse Emission Cygnus Region: Matter Density Contours overlaying Milagro Obs. 20 TeV profile in Cygnus Region w/GALPROP model TeV excess possibly due to: a. Unresolved sources? b. CR accelerators? pion component IC component

18. Gus Sinnis HAWC Review December 2007 Mrk 421: 7 Year Multi-Wavelength Campaign 7 year data set July 2000 - May 2007 No gamma/hadron cut (low energy) 64 day averaging period Average flux is 67% of the Crab Milagro - Events/day ASM Flux cts/s MJD - 50000 1/1/20001/1/20011/1/2002 1/1/2003 1/1/2004 1/1/2005 1/1/2006 1/1/2007 May-July 2005 5  excess during x- ray quiescent period Smith et al. ICRC 2007

19. Gus Sinnis HAWC Review December 2007 Significance Fractional Excess x10 3 B A A B Walker, et al. ICRC 2007 Anisotropy of TeV Sky

20. Gus Sinnis HAWC Review December 2007 Anisotropy: What is it? Excess is not gamma rays Region A has a hard spectrum & a cutoff Points to a nearby cosmic-ray accelerator

21. Gus Sinnis HAWC Review December 2007 Future Synoptic TeV Telescopes Complete summer 2007 Chinese-Italian collaboration 4300m asl (YBJ, Tibet) RPC carpet 10-15  /√year on Crab China-Japan collaboration 4300m asl (YBJ, Tibet) Tibet w/buried water tanks Emphasis 10-1000 TeV US-Mexico collaboration 4100m asl (Mexico) Water Cherenkov >100  /√year on Crab HAWC ARGO Tibet w/Muon Detectors

22. Gus Sinnis HAWC Review December 2007 Milagro has made large advances in TeV survey technology –Discovery of diffuse TeV gamma rays from the Galactic plane & Cygnus –Discovery of at least 3 Galactic TeV sources (point and extended) –Highest energy gamma rays detected > 100 TeV –Anomalous cosmic-ray anisotropy observed –Demonstration of long-term AGN monitoring (enabling multi- observations) Others are beginning to propose similar detectors –Tibet w/muon –IHEP and Chinese Academy of Sciences proposing HAWC-like detector (10 5 m 2 ) for 2013 construction date Lessons Learned from Milagro –Optical isolation is important (angular resolution & energy resolution) –Altitude is critical for low-energy response –Larger area needed (bkgd rejection, angular res., & HE response) We are uniquely qualified to extend this technology to the next phase Conclusions