Water Cherenkov Technology in Gamma-Ray Astronomy

Gus Sinnis

Los Alamos National Laboratory

Complementarity of Gamma-Ray Detectors Large Aperture/High Duty CycleMilagro, Tibet, ARGO, HAWC

Large Area

Good Background Rejection

Large Duty Cycle/Aperture

Sky Survey

Extended Sources

Transients (AGN, GRB)

Highest Energies

Galactic Diffuse Emission

Low Energy ThresholdEGRET/GLAST

Space-based (Small Area)

“Background Free”

Large Duty Cycle/Aperture

Sky Survey

AGN Physics

Transients (GRBs)

High SensitivityHESS, MAGIC, VERITAS

Large Area

Excellent Background Rejection

Low Duty Cycle/Small Aperture

High Resolution Spectra

Study of known sources

Limited Surveys

Fast Flaring

Distant AGN

Goals of a TeV Gamma-Ray Survey Instrument

• Galactic cosmic-ray origins– Galactic diffuse emission– Highest energies (>10 - 100 TeV)

• Particle acceleration in astrophysical jets– Gamma-ray bursts– Active galaxy transients– Multi-wavelength/messenger campaigns

• All-sky survey– Discovery potential– IACT alert system

Galactic Cosmic Rays

• Measure Galactic accelerators to >100 TeV• Measure diffuse emission spatial and spectrally

resolved– Large area (100,000 m2)– High duty factor (~100%)– Large field-of-view (~2 sr)

EGRET

Milagro

pion channel

Inverse Compton

channel

EGRET all sky (100 MeV)

Strong & Moskalenko

Cygnus Region

• Absorption by EBL requires– Low energy threshold– 200 GeV for z = 0.5 horizon– 1-2 TeV for z = 0.1 horizon

Extragalactic transients

Fermi/LATScienceExpress 2/19/2009

GBMLA

T

• Gamma-Ray Bursts– GeV ≥ 0.1 x MeV fluence– 10-7 ergs/cm2 @ 10 sec– 4000 m2 @ 200 GeV

GeV = 0.1 100keVGeV = 100ke

V

MAGIC collab.

Extensive Air Shower Arrays

http://www.ast.leeds.ac.uk/~fs/photon-showers.html

4 km

1 TeV

gamm

a-ray shower Longitudinal P

rofile

7.7 km

30 km

meters

• gammas• electrons

gamma:electron ratio ~6:1em particles sparse at low energiesneed enclosed area ~ active detector area 200 m

Tibet AS

Active detectors

Milagro

Effect of Altitude on Response

30% eff

7% eff

E-M Energy on Ground

5200 m Observatory

~10% of energy reaches the ground

Error on Mean

Background rejection in EAS arrays

’s within a 105 m2 area of core

Large fluctuations of shower size manifest as fluctuations

in muon content

Milagro – 1st Generation

8 meters

e

80 meters

50 meters

• 2600m asl

• 898 detectors

– 450(t)/273(b) in pond

– 175 water tanks

• 4000 m2 (pond) / 4.0x104 m2 (phys. area)

• 5-40 TeV median energy (analysis dependent)

• 1700 Hz trigger rate

• 400 Gbyte/day

• 0.3o-1.2o resolution (0.75o average)

• 95% background rejection (at 50% gamma eff.)

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

TeV Observations of Fermi Sources

• 34 Fermi BSL Galactic sources above declination of -5o

• 14 detected by Milagro above 3– FDR Miller 2001 estimates 1% false positive rate

• 5 new TeV sources

• Geminga 6.3 as extended source (2.6o fwhm)

Boomerang Cygnus Region

MGRO 1908+06HESS 1908+063

Geminga

Crab Nebula

Fermi Sources

GemingaPulsar

Milagro C3

Pulsar (AGILE/Fermi)

MGRO 2019+37

Fermi PulsarCygni SNR Fermi Pulsar

HESS 2032+41MGRO 2031+41

MAGIC 2032+4130

Fermi PulsarMilagro (C4)

3EG 2227+6122Boomerang PWN

IC433SNR

MAGICVERITAS

Radio pulsar J0631+10

(new TeV source)unID

(new TeV source)

unID(new TeV source)

Fermi PulsarMGRO 1908+06HESS 1908+063

W51HESS J1923+141

SNR

G65.1+0.6 (SNR)Fermi Pulsar (J1958)

New TeV sources

HAWC: The Next Generation

The base of volcán Sierra Negra• latitude : 18º 59’• longitude: 97º 18’• altitude : 4100mInside Parque Nacional Pico de Orizaba2 hours from Puebla (INAOE)

15x Milagro sensitivity 5x larger active detector area optical isolation of detector elements10x larger muon detector improved angular resolution improved energy resolution higher altitude (4100 m)1/3 median energy of Milagro

The HAWC Collaboration

Los Alamos National LaboratoryB. Dingus, J. Pretz, G. Sinnis

University of MarylandD. Berley, R. Ellsworth, J. Goodman, A.

Smith, G. Sullivan, V.Vasileiou

University of New MexicoJ. Matthews

University of UtahD. Kieda

Michigan State UniversityJ. Linnemann

Pennsylvania State UniversityTy DeYoung

NASA/GoddardJ. McEnery

Naval Research LabA. Abdo

UC Santa CruzM. Schneider

Instituto Nacional de Astrofísica Óptica y Electrónica

Alberto Carramiñana, L. Carasco, E. Mendoza,S. Silich, G. T. Tagle,

Universidad Nacional Autónoma de MéxicoR. Alfaro, E. Belmont, M. Carrillo, M. González, A. Lara,

Lukas Nellin, D. Page, V. A. Reese, A. Sandoval, G. Medina Tanco,O. Valenzuela, W. Lee

Benemérita Universidad Autónoma de PueblaC. Alvarez, A. Fernandez, O. Martinez, H. Salazar

Universidad Michoacana de San Nicolás de HidalgoL. Villasenor

Universidad de GuanajuatoDavid Delepine, Victor Migenes, Gerardo Moreno,

Marco Reyes, Luis Ureña UC Irvine

G. YodhUniversity of New Hampshire

J. Ryan

HAWC Design

900 tank array

4.3m high x 5m diameter tanks

100 MeV photons shown

Through-going Muon

150 m150 m

150

m15

0 m

HAWC: Background Rejection

Gam

mas

Pro

tons

Size of Milagro deep layer

Energy Distribution at ground level

Size of HAWC

Rejection Parameter: nPMT/cxPEnPMT = # PMTs in eventcxPE = Maximum # Pes in PMT > 30 m from fit core location

Background rejection

• Background rejection improves improves with increasing energy

• S/B 5x at E> 5 TeV (with rejection vs. no rejection)• Essentially background free near 100 TeV

hadrons

gammasMilagro

HAWC

Fra

ctio

n bk

gd r

emai

ning

HAWC: Effective Area

HAWC DC Sensitivity: 5-Year Survey

IACTs 50 hrs (~0.06 sr/yr)IACTs 50 hrs (~0.06 sr/yr)

1 yr1 yr

EAS 5 yrs (~2EAS 5 yrs (~2 sr) sr)

2000 km

2000 km22 sr

hr sr

hr

Survey Sensitivity

4 m

in/f

ov

7 m

in/f

ov1500 hrs/fov1500 hrs/fov

Sensitivity vs. Source Size

€

Sextended ≈ Spoint

σ source

σ detector

Large, low surface brightness sources require large fov and large observation time to detect.

EAS arrays obtain ~1500 hrs/yr observation for every source.

Large fov (2 sr):

Entire source & background simultaneously observable

Background well characterized

Brenda DingusHAWC Review - December 2007

AGN Monitoring• Measure TeV duty factors and notify other observers of flares in real time.

• Unbiased survey for TeV “orphan” flares• All sources within ~2 sr will be observed every day for ~ 5 hrs.• Continuous observations – no gaps due to weather, moon, or solar constraints. • HAWC’s 5 sensitivity is (10,1,0.1) Crab in (3 min, 5 hrs, 1/3 yr)

Worldwide Dataset of TeV Observations by IACTs of Mrk421

1 month

Tank Details• PMT at bottom of tank• Non reflective interior surfaces• Roto-molded tank issues

– Largest tanks available not deep enough– Too large for road transport (build on site)

Steel pipe with bladder

No size limitations, easy transportation (in pieces)

@ Sierra Negra

In CA

Conclusions• Water Cherenkov Technology enables a “low”-threshold all-sky

gamma-ray capability (sub-TeV)• First generation instrument built at moderate altitude demonstrated

the capability of the technique– Discovery of Galactic diffuse emission at 10 TeV (large excess observed)– Discovery of extended sources of TeV emission– Discovery of an anomalous component to the local cosmic rays– TeV counterparts to Fermi GeV sources (5 new TeV sources)

• The next generation instrument will have ~15x greater sensitivity– Build at high altitude (4100m)

• Scientific Goals– Origin of Galactic Cosmic Rays– Understanding Galactic accelerators (Pevatrons)– Extragalactic accelerators via multi-wavlength/messenger study of transients

• Active Galaxies (10x Crab in 3 minutes)• Gamma-ray bursts

• Funding received for R&D and site development ($1M)– 3 tanks operating on site– All permits for full array in place

• Proposal at NSF and DoE awaiting PASAG (Summer 2009)