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Gus SinnisHAWC Review December 2007
Milagro a TeV Gamma-Ray Observatory
Gus Sinnis
Los Alamos National Laboratory
Gus SinnisHAWC 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
Gus SinnisHAWC Review December 2007
Complementarity of TeV Gamma-Ray Detectors
Imaging Air Cherenkov Telescopes Extensive Air Shower Arrays
Energy Range .05-50 TeVArea > 104 m2
Background Rejection > 99%Angular Resolution 0.05o
Energy Resolution ~15%Aperture 0.003 srDuty Cycle 10%
Energy Range 0.1-100 TeVArea > 104 m2
Background Rejection > 95%Angular Resolution 0.3o - 0.7o
Energy Resolution ~50%Aperture > 2 srDuty Cycle > 90%
High Resolution Energy SpectraPrecision Study of Known SourcesSource Location & MorphologyDeep Surveys of Limited Regions of Sky
Unbiased Complete Sky Survey Extended SourcesTransient Objects (GRB’s & AGN) Multi-Wavelength/Messenger Observations
Gus SinnisHAWC Review December 2007
Current Generation EAS ArraysTibet AS
Milagro
Gus SinnisHAWC Review December 2007
Gus SinnisHAWC Review December 2007
Gus SinnisHAWC Review December 2007
25 Northern Hemisphere Sources
Whipple 4 (1969 - 2006)HEGRA 4 (1992 - 2002)Milagro 4 (+3*) (2000 - present)HESS 6 (2004 - present)MAGIC 7 (2005 - present)VERITAS (coming soon!)
Gus SinnisHAWC 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 m2 / 4.0x104 m2 • 2-12 TeV median energy • 1700 Hz trigger rate• 0.5o-1.4o resolution• 95% background rejection
Gus SinnisHAWC Review December 2007
Event Reconstruction
Measure time to <1 ns
Direction reconstruction 0.5o to 1.4o (size dependent)
Tim
e (n
s)
Gus SinnisHAWC Review December 2007
Background Rejection in MilagroProton MC Proton MC
Data Data MC 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
Gus SinnisHAWC Review December 2007
Background Rejection (Cont’d)
( )mxPE
nFitfOut+fTop=A
∗4
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 A4 to reject hadrons:A4 > 3 rejects 99% of Hadrons
retains 18% of Gammas
S/B increases with increasing A4
Background Rejection ParameterBackground Rejection Parameter
Gus SinnisHAWC Review December 2007
Distribution of Excesses in the Galactic Plane
cut level
CrabNebula
Mrk 421
• 6.5 year data set (July 2000-January 2007)• Weighted analysis using A4 parameter• Crab nebula 15 • Galactic plane clearly visibleCygnus
Region
Gus SinnisHAWC 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+60 EGRETE. Ona-Wilhelmi, et al., ICRC 2007
MGRO 1908+06
Gus SinnisHAWC Review December 2007
H.E.S.S. A&A 2006
~-2.0 Ec ~20 TeV
The Highest Energy Gamma Rays: HESSRX J1713.7-3946 HESS Observations
3 years of data 2003-2005
4.8 above 30 TeV
Gus SinnisHAWC 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
60 90
MGRO 1908+06
Gus SinnisHAWC Review December 2007
The Cygnus Region
C1 J2044+36
C2 J2031+33
MGRO J2031+41MGRO J2019+37
• MGRO J2019+37: 10.9σ – Extended source 1.1o ± 0.5o (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)
– 3.0o ± 0.9o (top hat dia.)• C1 J2044+36: 5.5σ pre-trials
– no counterparts– < 2.0o
• 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
Gus SinnisHAWC 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 componentIC component
Gus SinnisHAWC Review December 2007
Mrk 421: 7 Year Multi-Wavelength Campaign
7 year data set July 2000 - May 2007No gamma/hadron cut (low energy)64 day averaging periodAverage flux is 67% of the Crab
Mila
gro
- E
vent
s/da
y
AS
M F
lux
cts/
s
MJD - 500001/1/2000 1/1/2001 1/1/2002 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
Gus SinnisHAWC Review December 2007
Significance
Fractional Excess x103
B A
AB
Walker, et al. ICRC 2007
Anisotropy of TeV Sky
Gus SinnisHAWC 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
Gus SinnisHAWC Review December 2007
Future Synoptic TeV Telescopes
Complete summer 2007Chinese-Italian collaboration
4300m asl (YBJ, Tibet)RPC carpet
10-15 /√year on Crab
China-Japan collaboration4300m asl (YBJ, Tibet)
Tibet w/buried water tanksEmphasis 10-1000 TeV US-Mexico collaboration
4100m asl (Mexico)Water Cherenkov
>100 /√year on Crab
HAWC
ARGO
Tibet w/Muon Detectors
Gus SinnisHAWC 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 (105 m2) 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
Recommended