Particle Astrophysics with Ground-Based
Gamma-Ray
Telescopes
Frank Krennrich,
State University, VERITAS
ESAC Meeting,Iowa
Rex Ranch
16 April, 2004Collaboration
Outline
Science Motivation for astrophysical TeV Photons
Atmospheric Cherenkov Imaging Technique
Astrophysics results with Whipple 10m telescope
 blazar observations/Cosmic Infrared Background
Quantum Gravity with TeV flares
SGARFACE: ms-scale g-ray bursts from Primordial Black Holes
Future detectors (VERITAS, GLAST)
Summary
Argonne National Laboratory
28 April, 2004
Particle Astrophysics Connections
Neutrinos
MeV: sun, SN
GeV: atmosphere
g
n
GRB
g
g
1 Crab
(standard candle)
SNR
g
1020 eV
HE- particle astronomy:
Neutrinos
 TeV – PeV
Cosmic Rays  1018 - 1020 eV
g-rays
 20 MeV – 50 TeV
(also linked to X-rays via e- )
AGN
Argonne National Laboratory
n
(TeV – PeV)
28 April, 2004
(p, n, He++ …)
Cosmic-Ray
Spectrum
Direct Measurements
dN/dE = E-2.7
Indirect Measurements
Fixed
target
HERA
1912 HESS
Tevatron LHC
Argonne National Laboratory
Opacity of Universe
limited by:
p 28
+ April,
gCMB2004  p + p
g-rays from cosmic-ray beam dump
g-rays provide directional information
Probe proximity of acceleration sites
spg
• location of beam/accelerator
• g-ray spectrum  p-spectrum
• acceleration mechanism
Argonne National Laboratory
28 April, 2004
The Whipple 10m Telescope
Imaging
Camera
0.01 – 100 TeV
Argonne National Laboratory
Area ~ 100,000 m2
E ~ 0.2 – 100 TeV
Dq/q ~ 0.2 o
28 April, 2004
Cosmic Ray Rejection Technique
g-ray
proton
g-ray images:
- narrow, short, smooth
Hadronic images:
- broad, long
- local muons, patchy
hadron rejection: 99.7% (10-3)
Crab
Nebula
5o
7 s in
1hour
Argonne National Laboratory
28 April, 2004
Milestones with Whipple:
• 1989 Discovery of TeV
photons from the Crab
Weekes et al. 1989, ApJ, 342, 379
7 s per hour
• 1997 Flare
of Mrk 501
z = 0.034
hard-X-ray/TeV
correlation
Catanese et al. 1997, ApJ, 487, L143
• 2001 Discovery of H1426+428
• 1992 TeV
(z = 0.129)
photons from
Mrk 421
z = 0.031
Horan et al. 2000, Head Meeting, 23
05.03
Horan et al. 2002, ApJ,
Petry et al. 2002, ApJ, 580, 104
Punch et al. 1992, Nature, 358, 477
• 2001 Flare
• 1996 Giant
Mrk 421
 IR cutoff?
& short
flare
from
Mrk 421
Gaidos et al. 1996, Nature, 383, 319
Argonne National Laboratory
Krennrich et al. 2001,
ApJL, 560, L45
28 April, 2004
2004 Status: TeV Blazars!
Mrk 421
H1426+428
Mrk 501
1ES1959+650
1ES2344+514
1ES2155-304
TeV blazar
Mrk 421
Mrk 501
1ES2344
1ES1959
1ES2155
H1426
0.031
0.034
0.044
0.048
0.116
0.129
 70 “EGRET” blazars at 1 GeV with redshift z = 0.03 – 2.28
 6 “TeV” blazars (as of April 2004) with redshift z = 0.03 – 0.129
Argonne National Laboratory
28 April, 2004
1992
1995
1995
2002
2003
2001
TeV Activity: X-ray connection
RXTE ASM
strong TeV flares: 1996, 2000/01, 2002
strongest TeV flaring episode: feb. – aug. 1997
weak TeV detection: 1995/96, elusive since
weak TeV detection in 1999, strong flare in 2002
weak TeV detections: 2000, 2001
figure from Krawczynski et al. 2003, ApJ, 601, 151
Argonne National Laboratory
28 April, 2004
Light Curves: TeV/X-ray connection
Mrk 501
Mrk 421
Jordan et al. 2001, Proc. of the 27th ICRC, 2691
Argonne National Laboratory
28 April, 2004
The Broad (Wavelength) Picture
Argonne National Laboratory
28 April, 2004
Probing the Central Engine
(Gaidos et al., Nature, 383, 319 1996)
Argonne National Laboratory
28 April, 2004
Quantum Gravity Effects I
• Dispersion relation for photons
c2 p2 = E2 [1 + f(E/EQG )
Model dependent
function
effective QG energy scale
• Vacuum is a quantum gravitational medium
- vacuum responds differently to the propagation of
particles at different energies!
- medium contains quantum fluctuations occuring on the
size scale of the Planck length:
L P ~ 10-33 cm
Argonne National Laboratory
EQG ~ E P
~ 1019 GeV
28 April, 2004
Quantum Gravity Effects II
• Dispersion relation for photons
For small energies: E QG << E:  series expans.
V = dE/dp ~ c [ 1 – x E/EQG ]
Sign ambiguity x = +, -
• Time delay between photons of different energy
E1
t 1 = L/c[1- x E/E QG ]
E2
t 2 = L/c
E 1 >> E 2
Argonne National Laboratory
28 April, 2004
Quantum Gravity Effects III
• Time delay
Dt ~ (L/c) x E/E QG
Most likely noticable
if E & L large, Dt short
• Potentially relevant astrophysical Example:
Gamma Ray Bursts: GRB 910711 (Bhat et al. 359, 277, 1992)
Dt ~ 100 ms
L = ? but likely ~ 1010 … 1011 pc (GRBs: z = 1 – 4.5 observed)
E = 20 MeV
Argonne National Laboratory
 E QG ~ 1021 GeV
28 April, 2004
Quantum Gravity Effects IV
• Constraint from TeV data (Mrk 421 flare)
Dt ~ 15 min.
L = 130 Mpc (z = 0.03)
H 0 = 85 km/Mpc/s
Gaidos et al. 1996, Nature, 383, 319
Dt ~ (L/c) x E/E QG
Argonne National Laboratory
 E QG > 4 x 1016 GeV
Biller et al. 1999, Phys. Rev. Lett., 83, 2108
28 April, 2004
Cosmology: Extragalactic Background Light
Absorption:
exp(-t(E))
Source:
dN/dE ~ E-2
g-ray
Spectrum at earth:
E-2 exp(-t(E))
e+
IR-photon
e-
• EBL causes spectral distortion due to g + g  e+ + e• Optical depth depends on integral over the EBL spectrum
from the threshold for pair creation up to higher energies
and the distance to the g-ray source
Argonne National Laboratory
28 April, 2004
g-ray
X-ray
UV
Extragalactic
Background Light
(EBL)
Ground-based
g-ray astronomy
window
Optical
Infrared
CMB
Radio
EBL – TeV connection
Nikishov JETP 14, 2 (1962)
Gould & Schreder Phys. Rev. 155, 1408 (1967)
Stecker, de Jager, & Salamon ApJ 390, L42 (1992)
Ressell & Turner, 1989, FERMILAB-Pub-89/214-A
Argonne National Laboratory
g
28 April, 2004
EBL Detections & Limits
Bernstein et al. 2002
(HST WFPC, detections,
3 – 4 s, isotropic)
Wright 2001 (DIRBE
detections, 2-3 s)
Lagache et al. 2000 (FIRAS & DIRBE,
1 detection, 3 s, 2 upper limits)
Cambresy et al. 2001
(DIRBE detections at
1.25 & 2.2 mm, 3, 4 s)
Hauser et al. 1998 (Dirbe &
FIRAS, 140, 240 micron
detections, 3 – 4 s, isotropic)
Fixsen et al. 1998
(FIRAS, detections, 3 – 4 s)
Gardner et al. 2000
(STIS, galaxy counts,
lower limits)
Madau & Pozetti 2000
(HST, galaxy counts, strictly lower limits,
systematic underestimates ~ factor 2)
Elbaz et al. 2002,
(ISO, galaxy counts,
detection but only a
lower limit)
shaded area corresponds to de
Jager & Stecker 2001
data from review by Hauser & Dwek, ARA&A, 39, 249 (2001)
figure from Dwek & Krennrich 2004, submitted to ApJ
Argonne National Laboratory
28 April, 2004
Observational Evidence for g-ray Absorption
Mrk 501 (z= 0.03)
Samuelson et al. 1998, ApJ, 501, L17
Mrk 421 (z=0.03)
Krennrich et al. 2001, ApJ, 560, L45
H1426+428 (z=0.13)
Petry et al. 2002, ApJ, 580, 104
1Es1959+428 (z=0.048) preliminary!
Daniel et al. 2004, in preparation
-
Mrk 421 & Mrk 501 show cutoff at similar energy ~ 4 TeV
- 1ES2344+514, 1ES1959+659, H1426+428 show increasingly
steeper spectrum
 attenuation due to Extragalactic Background Light?
Argonne National Laboratory
28 April, 2004
Primordial Black Hole Search
SGARFACE:
Short GAmma Ray Front Air
Cherenkov Experiment
Stephan LeBohec, Bagmeet Bherera, Patrick Jordan, Gary Sleege & Frank Krennrich
Argonne National Laboratory
28 April, 2004
Primordial Black Holes: Evaporation
• Mass of presently evaporating:
1014 - 1015 gram
~ mass of comet Halley
• Schwarzschild radius:
10-15 m
S. W. Hawking, Nature, 248, 31 (1974)
Argonne National Laboratory
~ size of hydrogen nucleus
28 April, 2004
Primordial Black Holes: Evaporation
T ~ (1013gram/M) [GeV]
Temperature T
P ~ dM/dt ~ -a(M)/M2
Power P
t ~ 1010 yr [M/1012 kg ]3
Lifetime t
Hawking, S.W., Nature, 248, 30 (1974)
Standard model
of particle physics:
Truth
 1s burst at E > 1 TeV
somewhere in
Hagedorn model:
between!
-7
 10 s burst at E > 200 MeV
Argonne National Laboratory
28 April, 2004
Particle Spectrum: PBH @ T =1 GeV
E > 50 MeV
g
p+p
Argonne National Laboratory
28 April, 2004
Burst Detection Technique:
Background reduction:
0.1 – 10 ms burst profile:
 long Cherenkov pulse
Imaging:
 characteristic shape
 extremely smooth
No parallax:
 VERITAS
Krennrich, Le Bohec & Weekes, ApJ, 529, 506 (2000)
Argonne National Laboratory
28 April, 2004
Burst Detection with VERITAS:
1. Burst trigger in one or 2. FADC system allows
recording of slow pulses
several telescopes
Argonne National Laboratory
28 April, 2004
Sensitivity of SGARFACE to PBHs:
Argonne National Laboratory
28 April, 2004
Fluence Sensitivity to Burst:
100 ns burst of
250 MeV g-rays
Min. photon density:
~ 0.1 g’s/m2
Argonne National Laboratory
28 April, 2004
Signal Splitters/Summers
From
PMT
To TeV
Electronics
To SGARFACE
Electronics
379PMT -> 55 channels
Argonne National Laboratory
28 April, 2004
Prototype Experiment:
Short GAmma Ray Front Air Cherenkov Experiment I
379
Signal
Splitter &
Summer
379
TeV
electronics
55
VME
Data
acquisition
Trigger
Level 1
(multi-time
scale discr.
60ns-30ms)
55 x 6
Pattern
Coincidence
Unit
STOP
GPS
Argonne National Laboratory
28 April, 2004
Multi-Time- Scale Discriminators
60ns, 180ns, 540ns, 1.6ms,
4.8ms & 14.6ms
4 x 16 = 64
Argonne National Laboratory
28 April, 2004
Pattern Sensitive Topological Trigger
Argonne National Laboratory
28 April, 2004
60ns
180ns
540ns
Argonne National Laboratory
1620ns
4860ns
28 April, 2004
14580ns
60ns
180ns
540ns
Argonne National Laboratory
1620ns
4860ns
28 April, 2004
14580ns
60ns
180ns
540ns
Argonne National Laboratory
1620ns
4860ns
28 April, 2004
14580ns
Bias curves under multiplicity 3
60ns
1.62ms
180ns
540ns
4.86ms
Argonne National Laboratory
28 April, 2004
Simulated
bursts
Real data
Argonne National Laboratory
28 April, 2004
Next Generation Telescopes
VERITAS,
2004 1 tel.
2006 4 tel.
2008 7 tel.
HESS, 4 tel., 2004
MAGIC, 1 tel.,
2003+
CANGAROO III, 4 tel., 2005
• Multiple facilities separated by longitude and latitude:
good global coverage and effective multiwavelength observations
• VERITAS & MAGIC observe same sources as IceCube.
• GLAST launch: worldwide VHE network follow up observations
Argonne National Laboratory
28 April, 2004
Next-generation Telescopes
Location Altitude Mirrors Stereo? FOV
Peak Energy
NORTH
VERITAS-4 Arizona
VERITAS-7 Arizona
MAGIC
La Palma
1.8 km
1.8 km
2.2 km
4 x 112m2
7 x 112m2
1 x 225m2
Yes
Yes
No
3.5o
3.5o
2.4o
100 GeV
80 GeV
86 GeV
SOUTH
HESS
Namibia
CANGAROO Australia
1.8 km
0.2 km
4 x 112m2
4 x 80m2
Yes
Yes
4.8o
3.5o
96 GeV
148 GeV
Argonne National Laboratory
28 April, 2004
Improvements with VERITAS-4
“Stereo” technique + “modern” 12m telescope
• improved angular resolution
• better background rejection
• lower energy threshold
• improved energy resolution
• cross-calibration with GLAST
 absolute energy calibration
VERITAS-4
- 50 GeV – 50 TeV
- Dq/q ~ 0.03o @1TeV
~ 0.09o @100GeV
- Flux sensitivity:
15 mCrab @100GeV
5 mCrab @300GeV
80 m
Argonne National Laboratory
28 April, 2004
VERITAS Site:
- Horseshoe Canyon
(Kitt Peak N.O.)
- Arizona clear skies
- Dark site,
well shielded by
surrounding hills
- 1 km to Kitt Peak
Facility
- Easy access
- elevation ~ 1.8 km
Argonne National Laboratory
28 April, 2004
Time resolved imaging: Movies
Time resolved imaging
Courtesy of Stephan LeBohec & Michael Daniel
Argonne National Laboratory
28 April, 2004
Spectral Variability
6 min @ 4.5 Crab
VERITAS will achieve
comparable hour-scale
sensitivity making time resolved
spectral measurements not
possible with any other
technique above a few keV.
Probe intrinsic variability
timescales.
Discriminate between a fixed
external absorption feature and
variable intrinsic curvature.
27 min @ 2.8 Crab
6 min @ 1.2 Crab
Argonne National Laboratory
(Krennrich, 2002)
28 April, 2004
Sensitivity
Argonne National Laboratory
28 April, 2004
Summary
Gamma Rays are probing:
 cosmic rays: g-ray connection via p0
 astrophysical sources: active galaxies, compact objects
 cosmology: g-ray absorption, Cosmic IR Background
 particle physics: Primordial Black Holes, Dark Matter
 fundamental physics: Quantum Gravity
Astrophysics
 powerful technique available to
SGARFACE: ms-scale g-ray burst experiment
Future detectors (VERITAS, GLAST)
Summary
Argonne National Laboratory
28 April, 2004