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

Gus SinnisHAWC Review December 2007

Milagro a TeV Gamma-Ray Observatory

Gus Sinnis

Los Alamos National Laboratory


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


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


Current Generation EAS ArraysTibet AS

Milagro




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!)


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


Event Reconstruction

Measure time to <1 ns

Direction reconstruction 0.5o to 1.4o (size dependent)

Tim

e (n

s)


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


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


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


• 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


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


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


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


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


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


Significance

Fractional Excess x103

B A

AB

Walker, et al. ICRC 2007

Anisotropy of TeV Sky


Anisotropy: What is it?

• Excess is not gamma rays

• Region A has a hard spectrum & a cutoff

• Points to a nearby cosmic-ray accelerator


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


• 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

Documents

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