Water Cherenkov Technology in
Gamma-Ray Astronomy
Gus Sinnis
Los Alamos National Laboratory
Complementarity of Gamma-Ray Detectors
Low Energy Threshold
EGRET/GLAST
High Sensitivity
HESS, MAGIC, VERITAS
Large Aperture/High Duty Cycle
Milagro, Tibet, ARGO, HAWC
Space-based (Small Area)
Large Area
Large Area
“Background Free”
Excellent Background Rejection
Good Background Rejection
Large Duty Cycle/Aperture
Low Duty Cycle/Small Aperture
Large Duty Cycle/Aperture
Sky Survey
High Resolution Spectra
Sky Survey
AGN Physics
Study of known sources
Extended Sources
Transients (GRBs)
Limited Surveys
Transients (AGN, GRB)
Fast Flaring
Highest Energies
Distant AGN
Galactic Diffuse Emission
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)
Cygnus Region
Milagro
Strong & Moskalenko
EGRET all sky (100 MeV)
Extragalactic transients
• Absorption by EBL requires
• Gamma-Ray Bursts
– Low energy threshold
– GeV ≥ 0.1 x MeV fluence
– 200 GeV for z = 0.5 horizon
– 10-7 ergs/cm2 @ 10 sec
– 1-2 TeV for z = 0.1 horizon
– 4000 m2 @ 200 GeV
MAGIC collab.
LAT
Fermi/LAT
ScienceExpress 2/19/2009
GBM
Extensive Air Shower Arrays
http://www.ast.leeds.ac.uk/~fs/photon-showers.html
• gammas
• electrons
30 km
Milagro
meters
7.7 km
Active detectors
4 km
gamma:electron ratio ~6:1
em particles sparse at low energies
need enclosed area ~ active detector area
1 TeV gamma-ray shower Longitudinal Profile
Tibet AS
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
•
•
•
•
•
•
•
•
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.)
e


8 meters
50 meters
80 meters
Background Rejection in Milagro
Proton MC
Proton 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
 MC
 MC
Data
Data
Background Rejection (Cont’d)
Background Rejection Parameter
A4

fTop + fOut   nFit
=
mxPE
Apply a cut on A4 to reject hadrons:
A4 > 3 rejects 99% of Hadrons
retains 18% of Gammas
S/B increases with increasing A4
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
TeV Observations of Fermi Sources
Boomerang
Cygnus Region
MGRO 1908+06
HESS 1908+063
Fermi Sources
Geminga
Crab Nebula
•
•
34 Fermi BSL Galactic sources above declination of -5o
14 detected by Milagro above 3s
–
•
•
FDR Miller 2001 estimates 1% false positive rate
5 new TeV sources
Geminga 6.3s as extended source (2.6o fwhm)
IC433
SNR
MAGIC
VERITAS
Radio pulsar
J0631+10
(new TeV source)
G65.1+0.6 (SNR)
W51
HESS J1923+141 Fermi Pulsar (J1958)
New TeV sources
SNR
Geminga
Pulsar
Milagro C3
Pulsar
(AGILE/Fermi)
MGRO 2019+37
unID
(new TeV source)
Fermi Pulsar
Cygni SNR
Fermi Pulsar
HESS 2032+41
MGRO 2031+41
MAGIC 2032+4130
unID
(new TeV source)
Fermi Pulsar
MGRO 1908+06
HESS 1908+063
Fermi Pulsar
Milagro (C4)
3EG 2227+6122
Boomerang PWN
HAWC: The Next Generation
15x Milagro sensitivity
5x larger active detector area
optical isolation of detector elements
10x larger muon detector
improved angular resolution
improved energy resolution
higher altitude (4100 m)
1/3 median energy of Milagro
The base of volcán Sierra Negra
• latitude : 18º 59’
• longitude: 97º 18’
• altitude : 4100m
Inside Parque Nacional Pico de Orizaba
2 hours from Puebla (INAOE)
The HAWC Collaboration
Los Alamos National Laboratory
B. Dingus, J. Pretz, G. Sinnis
University of Maryland
D. Berley, R. Ellsworth, J. Goodman, A.
Smith, G. Sullivan, V.Vasileiou
University of New Mexico
Instituto Nacional de Astrofísica Óptica y
Electrónica
Alberto Carramiñana, L. Carasco, E. Mendoza,
S. Silich, G. T. Tagle,
Universidad Nacional Autónoma de México
University of Utah
R. 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
D. Kieda
Benemérita Universidad Autónoma de Puebla
Michigan State University
C. Alvarez, A. Fernandez, O. Martinez, H. Salazar
J. Matthews
J. Linnemann
Pennsylvania State University
Ty DeYoung
Universidad Michoacana de San Nicolás de Hidalgo
L. Villasenor
Universidad de Guanajuato
NASA/Goddard
David Delepine, Victor Migenes, Gerardo Moreno,
Marco Reyes, Luis Ureña
J. McEnery
UC Irvine
Naval Research Lab
A. Abdo
UC Santa Cruz
M. Schneider
G. Yodh
University of New Hampshire
J. Ryan
HAWC Design
100 MeV photons shown
Through-going Muon
900 tank array
4.3m high x 5m diameter tanks
Gammas
HAWC: Background Rejection
Protons
Size of HAWC
Size of Milagro
deep layer
Energy Distribution at ground level
Rejection Parameter: nPMT/cxPE
nPMT = # PMTs in event
cxPE = Maximum # Pes in PMT > 30 m from fit core location
Background rejection
gammas
hadrons
Fraction bkgd remaining
• 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
Milagro
HAWC
HAWC: Effective Area
HAWC DC Sensitivity: 5-Year Survey
IACTs 50 hrs (~0.06 sr/yr)
EAS 5 yrs (~2 sr)
7 min/fov
1500 hrs/fov
4 min/fov
Survey Sensitivity
1500 hrs/fov
Sensitivity vs. Source Size
Large, low surface brightness
sources require large fov and
large observation time to detect.
Sextended
s source
 Spoint
s detector
EAS arrays obtain ~1500 hrs/yr
observation for every source.

Large fov (2 sr):
Entire source & background
simultaneously observable
Background well characterized
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 s 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
Brenda Dingus
HAWC Review -
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)
@ Sierra Negra
In CA
Steel pipe with bladder
No size limitations, easy
transportation (in pieces)
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)