Astrophysics with
2 sr and 24/7
VHE Detectors
Brenda Dingus for the
Milagro and HAWC
collaborations
Brenda Dingus
20 Oct 2005
Milagro Gamma Ray Observatory @ 8600’ altitude near Los Alamos, NM
Abdo9, R.Atkins,1,2 W. Benbow,3,4 D. Berley,5 E. Blaufuss5, D.G. Coyne,3 T.
DeYoung,3,5 B.L. Dingus,6 D.E. Dorfan,3 R.W. Ellsworth,7 L. Fleysher,8 R.Fleysher8,
M.M. Gonzalez,1,14 J.A. Goodman5, E. Hays5, C.M. Hoffman,6
C.P. Lansdell,5 J.T. Linnemann,9 J.E. McEnery,1,10 A.I. Mincer,8 M.F. Morales,3,11
P. Nemethy,8 D. Noyes,5 J.M. Ryan,12 F.W. Samuelson,6 P.M. Saz Parkinson,3
Shoup,13 G. Sinnis,6 A.J. Smith,5 G.W. Sullivan,5 D.A. Williams,3 X.W. Xu6
and G.B. Yodh13
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Department of Physics, University of Wisconsin
Current Address: Department of Physics, University of Utah
Santa Cruz Institute for Particle Physics, University of California, Santa Cruz
Current address: Max-Plank-Institute fur Kernphysik
Deoartment of Physics, University of Maryland
Los Alamos National Laboratory
Department of Physics and Astronomy, George Mason University
Department of Physics, New York University
Department of Physics and Astronomy, Michigan State University
Current address: NASA Goddard Space Flight Center
Current address: Massachusetts Institute of Technology
Department of Physics, University of New Hampshire
Department of Physics and Astronomy, University of California, Irvine
UNAM, Mexico City
Brenda Dingus
20 Oct 2005
Water Cherenkov Detectors
• Detect Particles in Extensive Air Showers from
Cherenkov light created in a covered pond
containing filtered water.
• Reconstruct shower direction from the time
different photodetectors are hit.
• Multi-kHz trigger rate mostly due to Extensive
Air Showers created by cosmic rays
• Field of view is ~2 sr and the average duty
factor is nearly 100%
Milagro Cross Section Schematic
e
m
g
8 meters
50 meters
80 meters
Brenda Dingus
20 Oct 2005
Milagro, miniHAWC, HAWC
 Design details about miniHAWC and HAWC are in other presentations.
 #s below depends on source spectrum and declination plus trigger cuts.
– Crab spectrum of dN/dE a E-2.59 was assumed.
– Background was normalized from Milagro observations.
– Detector latitude is arbitrarily same as Milagro, so Crab transits at 15o
Median
Energy
Angular Time for 5s
on Crab
Res.
mCrab/day
@ 5s
mCrab/month
@ 5s
mCrab/year
@ 5s
Milagro w/o
outriggers
3 TeV
0.75o
1.1 years
21,000
3,800
1,200
Milagro
3 TeV
0.5o
½ year
13,000
2,500
700
miniHAWC
700 GeV
0.4o
2 days
1,700
300
70
HAWC
250 GeV
0.3o
½ hour
300
50
15
Brenda Dingus
20 Oct 2005
Sensitivity of Milagro to the Crab Nebula
Pre-Outrigger – data since 2000
• Optimized with MC simulations
• Published detection of the Crab
(ApJ 595, 803 (2003))
• Sensitivity: ~4.7s/yr on the Crab
• 10.0s from 4.5yr
Post-Outrigger – data since 2003
• Good angular reconstruction on
off-pond cores
• Sensitivity: ~8s/yr on the Crab
• 9.7s from 1.5yr
Brenda Dingus
20 Oct 2005
Predicted TeV AGNs
Standard
Deviations
 1-year HAWC observation
 Costamante & Ghisellini AGN
(31 sources)
 Kneiske, Hartmann, Mannheim
2005 IR model absorption
model
 + known TeV sources
# of C&G AGN > 5 sigma
30
25
20
15
10
 HAWC can monitor multiple AGN on
daily to monthly timescales
5
0
1day
1month
0.5 yr
1yr
2yr
4yr
HAWC Observation Time
Brenda Dingus
20 Oct 2005
GLAST AGNs
Dermer & Davis, 1999
•
•
•
•
BL Lacs will be largest fraction of GLAST AGN.
Many will not be known at other wavelengths.
GLAST localization at flux threshold ~20’.
HAWC sensitivity extrapolated as E-2 down to
100 MeV is ~ GLAST flux threshold.
• HAWC detection of GLAST sources would
constrain redshift, location, and variability as
well as point to targets for air Cherenkov
telescopes.
Brenda Dingus
20 Oct 2005
Energy Measurement
Average Energy vs Compactness
Milagro is sensitive to energy above the median detected energy of 3 TeV.
HAWC should have similar capabilities above it’s median energy of 250 GeV.
Brenda Dingus
20 Oct 2005
GRBs
 Rate of Satellite Triggers
is Low
– SWIFT 2/week
– GLAST GBM 4/week
but ~4o position error
– GLAST LAT detection
(10 g > 30 MeV)
~1/week with rapid
positions ~1/month
 HAWC fov ~1/6 of sky
and duty factor ~100%
so ~1 GRB/week is
searched for VHE
emission
 HAWC will detect even
high z GRBs IF VHE
fluence is ~ keV fluence
Lines are 5s sensitivity to a known
location within 20o of zenith
Brenda Dingus
20 Oct 2005
High Energy Component in GRBs
Combined EGRET-BATSE
observation shows a new high
energy component with hard
spectrum and more fluence.
GRB940217
(Gonzalez, 2003 Nature 424, 749)
GRB941017
The highest energy gamma-ray detected by
EGRET from a GRB was ~20 GeV and was over
an hour late. (Hurley, 1994 Nature 372, 652)
Milagrito’s > 650
GeV observation
implies a new
mechanism with
greater fluence
than synchrotron.
(Atkins, 2003, Ap J
583 824)
GRB970417
Brenda Dingus
20 Oct 2005
VHE & GRBs
Razzaque, Meszaros & Zhang 2004
 VHE Prompt
emission
constrains bulk
Lorentz factors
due to opacity in
source
 VHE early
afterglow probes B
field and electron
energy densities
 VHE lightcurve
constrains
quantum gravity
HAWC
Median Energy
Zhang & Meszaros 2001
1min
1 hr
1 day
1month
HAWC
Median Energy
Brenda Dingus
20 Oct 2005
Searching for VHE transients



HAWC data can be searched for VHE transient within a few seconds
Milagro search yields model dependent limit on VHE fluence from GRBs
Model assumptions will be better constrained by SWIFT and GLAST
(1) Assumptions:
redshift
T90
Eiso
(3) Upper Limit on VHE Emission:
(2) Predictions:
Brenda Dingus
20 Oct 2005
Other Transients
 X-ray binaries
– PSR1259-63 has low
duty cycle as
observed by HESS
for few months out of
3.4 year elliptical orbit
 Microquasars
– Variable at other
wavelengths
Brenda Dingus
20 Oct 2005
HESS Galactic Sources
 PWN, SNR, & UnID
 Most HESS detections
in the Galactic Plane
are extended sources
 Flux of HESS Sources
is 2-20% of Crab Flux
>300 GeV
 Largest Source is Vela
Jr with diameter of 2
degrees
(F. Aharonian et al.,
Astron. Astrophys.
437 (2005) L7-L10)
Brenda Dingus
20 Oct 2005
Milagro Galactic Source
 Milagro excess in overlapping 5.9o bins in left fig.
 Milagro excess convolved with 0.75o psf in right fig.
HEGRA detected TeV
Source: TEV J2032_4130.
EGRET Diffuse Model
PSF
Brenda Dingus
20 Oct 2005
EGRET Unidentified Sources & Milagro Morphology
1
2
3
4
5
6
7
3EG J2016+3657
3EG J2020+4017
3EG J2021+3716
3EG J2022+4317
3EG J2027+3429
3EG J2033+4118
3EG J2035+4441
F > 100 MeV/cm2s
(34.7 ± 5.7) x 10-8
(123. ± 6.7) x 10-8
(59.1 ± 6.2) x 10-8
(24.7 ± 5.2) x 10-8
(25.9 ± 4.7) x 10-8
(73.0 ± 6.7) x 10-8
(29.2 ± 5.5) x 10-8
g
2.09
2.08
1.86
2.31
2.28
1.96
2.08
7
4
6
3rd EGRET Catalog sources
shown with 95% position
error circle.
Flux of maximum point: 500mCrab
(May be extended)
2
3
1
5
Brenda Dingus
20 Oct 2005
VHE Emission from Cosmic Rays
 Molecular Clouds
– GLAST predicted to
detect >100 molecular
clouds (Torres, et al
2005)
– Measures ratio of CO to
Molecular Hydrogen and
samples cosmic ray
spectrum outside solar
neighborhood
 LMC and SMC
 Starburst Galaxies
 Galaxy Clusters
Maddalena, 1986
Brenda Dingus
20 Oct 2005
Milagro’s Observation of the
Galactic Plane (-2O<b<2O)
Consider Region l = 20O-100O
Weighted Map:
7.5s
Exclude the Cygnus Region: l=20O-75O
Weighted Map:
5.8s
Galactic longitude 20-75 excludes Cygnus region
Galactic longitude 20-100 includes Cygnus region
s=1.42 +/- .26
Brenda Dingus
20 Oct 2005
Integral Flux: Milagro & EGRET
E-2.51±0.05
Submitted to PRL
R1 (Gal. Long. 40 to 100 deg)
 Based on 3ys of data, 4.5s
 Flux(>3.5 TeV)
= (6.8±1.5±2.2)x10-11 cm-2 sec-1 sr-1
 Spectral Index to connect with EGRET
= -2.61± 0.03±0.05
 With outriggers we can measure the
spectrum at TeV energies
 2 more years of data needed for ±0.1
on spectral index at TeV energies
R2 (Gal. Long. 140 to 200 deg)
 Flux(>3.5 TeV)
< 4 x 10-11cm-2 sec-1 sr-1 (99% c.l.)
 Spectral index to connect with EGRET
< -2.66 (99% c.l.)
 Not yet a crisis but spectrum may be
softer in outer Galaxy
 Additional data will tell
Brenda Dingus
20 Oct 2005
Brenda Dingus
20 Oct 2005
Summary
 Water Cherenkov Technique has been proven to
work and is discovering new VHE phenomena
 Future Water Cherenkov Detectors can have the
sensitivity to
– Detect multiple sources daily
– Survey the sky for pt sources >1% of the Crab flux
above 250 GeV in 2 years (5 s)
– Search 2 sr of the sky for short duration transients
with nearly 100% duty factor
– Explore the morphology of extended sources such as
the Galactic plane and molecular clouds
Brenda Dingus
20 Oct 2005