Gamma-ray Astrophysics
with
ground-based detectors
Colloquium, UCLA,
October 16, 2002
e-, p?, n?
Frank Krennrich
Iowa State University
AGN
Outline
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Introduction
 general connections to particle astrophysics
 cosmic ray – g-ray connection via p0
 g-ray absorption by extra-gal. backgound. light (EBL)
 atmospheric Cherenkov imaging technique
Astrophysics results with Whipple 10m telescope
 blazar observations
 IR background – spectral cutoffs
SGARFACE: ms-scale g-ray burst experiment
Future detectors (VERITAS, GLAST)
Summary
Particle Astrophysics Connections
Neutrinos
MeV: sun, SN
GeV: atmosphere
g
n
GRB
g
g
1 Crab
(standard candle)
SNR
g
1020 eV
6/28/2016
AGN
HE- particle astronomy:
Neutrinos
 TeV – PeV
Cosmic Rays  1018 - 1020 eV
g-rays
 20 MeV – 50 TeV
(also linked to X-rays via e- )
n
(TeV – PeV)
3
(p, n,
He++
…)
Cosmic-Ray
Spectrum
Direct Measurements
dN/dE = E-2.7
Indirect Measurements
Fixed
target
HERA
1912 HESS
Tevatron LHC
Opacity of Universe
limited by:
p+ g
p+p
CMB
g-rays from cosmic-ray
beam dump
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g-rays provide directional information
Probe proximity of acceleration sites
spg
• location of beam/accelerator
• g-ray spectrum  p-spectrum
• acceleration mechanism
Active galactic nuclei
TeV e-
160 kpc
Copyright c NRAO/AUI 1999
Jets from Radio Galaxy 3C296
M87
Conceptional View:
160 kpc
Copyright c NRAO/AUI 1999
Jets from Radio Galaxy 3C296
It’s a blazar!
synchrotron-self-Compton (SSC):
- TeV e-  synchrotron X-rays
- TeV e- inv. Compton (opt. photons)  g-rays
- correlation X-ray/g-ray (optical)
- VHE g-ray/ X-ray spectra vary together
Proton induced cascades (PIC):
- acceleration  large B-fields required ~ 10 G
- target: synch. photons (spg ~ 10-3 seg) efficiency 7
- assumption: EHE 1019 eV
- g-rays come before X-rays
-  n’s, VHE g-rays, EHE-protons
external inverse-Compton:
- various target photon fields (CMB, IR dust)
- X-ray/g-ray correlation more complex
“beam meets target”
- guaranteed component from CMB
Proton synchrotron radiation:
- proton synch. Emission (Psynch.~ (mp /me)4 )
 EHE protons & large -fields (30 – 100 G)
- VHE g-rays, no n’s
- spectral variation slower than in SSC/EC
g-ray absorption
g + g g
CMB
+
e
+
e
1,000 TeV g-rays do not reach us from the edge
of our galaxy because of their small mean
free path in the microwave background.
Propagation of g-rays in the
diffuse photon background
gCMB g100TeV
g
e+
gIR gTeVg
eLog(E/eV)
2.7 K
e+ e-
30 – 3000 K
 measure EBL density with
10GeV – 50 TeV beams
IR
X-ray
GeV
g-ray
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Cosmic
rays
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Science with EBL:
direct mid-IR/near-IR
measurements background
limited (e.g., zodiacal light)
era of galaxy formation
star formation
dark matter scenarios
Probing the Universe with
VHE- g-ray Beams from Blazars
Source:
dN/dE ~ E-2
Spectrum at earth:
E-2 exp(-t(E))
Absorption:
exp(-t(E))
g-ray
e+
IR-photon
e-
Detection of g-rays
from satellites
EGRET
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30 MeV – 10 GeV
Sampling calorimeter
Anti-coincidence
shield (10 -6 )
Good C.R. rejection
Large f.o.v. (0.4 sr)
Small collection area:
2
EGRET was 0.16 m
History of the Whipple 10m
0.01 – 100 TeV
Imaging Camera
Area ~ 100,000 m2
E ~ 0.2 – 100 TeV
Dq/q ~ 0.2 o
100 optical photons/m2 TeV
within a few ns
Cosmic Ray Rejection Technique
g-ray
proton
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Courtesy W.Hofmann
Crab Nebula
7 s in 1hour
g-ray images:
- narrow, short, smooth
Hadronic images:
- broad, long
- local muons, patchy
hadron rejection: 99.7% (10-3)
Science Highlights: Whipple 10m
• 1989 Discovery of TeV
photons from the Crab
• 1997 Flare of Mrk 501
z = 0.034
Weekes et al. 1989, ApJ, 342, 379
37
• 1992 TeV photons from
the blazar Mrk 421
z = 0.031
Catanese et al. 1997, ApJ, 487, L143
151
• 2001 Discovery of
1H1426+428
(z = 0.129)
Horan et al. 2002, ApJ, 571, 753
Petry et al. 2002, ApJ, in press
Punch et al. 1992, Nature, 358, 477
109
• 1996 Giant & short flare
from
Mrk 421
~10 Crab
Gaidos et al. 1996, Nature, 383, 319
109
489
• 2001 Flare Mrk 421
Krennrich et al. 2001, ApJL, 560, L45
Krennrich et al. 2002, ApJL, 575, L9
489
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> 70 “EGRET” blazars at 1 GeV
Redshift z = 0.03 – 2.28
Mrk 421
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“Whipple”
blazars
at 300 GeV
z
H1426+428
Mrk 421
Mrk 501
1ES2344
1ES1959
H1426
Mrk 501
1ES1959+650
1ES2344+514
3C66
1ES2155-304
TeV blazar
0.031
0.034
0.044
0.048
0.129
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Mrk 421
z = 0.031
X-ray BL
Weak GeV
> 86 s TeV
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Mrk 501
z = 0.034
X-ray BL
Marginal GeV
> 40 s TeV
Multiwavelength spectra
Mrk 501
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Peak: 100 keV/200 GeV
X-ray/TeV correlation
Catanese et al., ???
Catanese & Weekes, PASP, 111, 3191193 (1999)
Mrk 421
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Peak at 1 keV/~50 GeV
X-ray/TeV correlation
Mrk 421/Mrk 501 spectra
Mrk 501
dN/dE ~ E-1.95 K 0.07 e –(E/E
)
with E0 = 4.6 K 0.8 TeV
Samuelson et al. 1998, ApJL, 501, L17
Krennrich et al. 1999, ApJ, 511, 149
Mrk 421
dN/dE ~ E-2.14 K 0.03 e –(E/E
)
with E0 = 4.3 K 0.3 TeV
(- 1.4 + 1.7 TeV)syst
Krennrich et al. 2001, ApJL, 560, L45
Mrk 421 <spectral variability>
 on average, g-ray
luminosity peak
shifts to larger energies
with increasing flux!
Krennrich, F. et al. 2002, ApJL, 575, L9
<Mrk 501> 1997 vs.
Mrk 421 high state
Mrk 501 1997 average
 spectral index varies
but cutoff region
remains stable!
imagine instrument
with 10 times the
sensitivity of Whipple
 separate time variable
from constant features
Mrk 421 high state (set I)
 IR-background density
Mrk 421: spectral variability:
VHE-g-ray
Krennrich et al. 2002, ApJL, 575, L9
X-ray
Fossati et al. 2000, ApJ, 541, 166
Krennrich et al. 1999, ApJ, 511, 149
Property of a specific blazar or emission mechanism?
½ Hourly Spectral Variability:
Feb. 2
Feb. 1
Feb. 27
P = 3.4 x 10-3
March 19
March 25
March 27
P = 8.5 x 10-4
P = 4.0 x
10-3
X-ray/TeV correlation: Mrk 421
X-ray/TeV lightcurve
Courtesy of G. Fossati , J. Buckley & M. Jordan
TeV lightcurve &
TeV spectral variation
VERITAS collaboration (in preparation)
Conclusion from
blazar observations
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Spectral cutoffs for Mrk 421/501 at ~ 4 TeV:
 possible evidence for absorption from IR background
 or due to internal break due to sKN ~ E-1 (when ghnsoft > me c2 )
Rapid variability (Mrk421):
 tvariability ~ 15 min.  g ~ 10  emission region 10-4 - 10-5 pc
X-ray/TeV correlation:
 in SSC models correlation should be tight
 in PIC models g-rays proceed X-rays, protons ????
Spectral variability (Mrk 421):
 g-ray luminosity peak shifts with <flux> increase (sim. X-rays)
 a-flux correlation holds over 5 years!
Next steps:  short term spectral variability in TeV/X-rays
 larger blazar sample to measure IR background
SGARFACE:
Short GAmma Ray Front
Air Cherenkov Experiment
Primordial Black Holes?
- Science
- Technique
- Status October 2002
Frank Krennrich, Stephan LeBohec, Gary Sleege & Patrick Jordan
Evaporation of Primordial
Black Holes
• Mass of presently evaporating:
1014 - 1015 gram
~ mass of comet Halley
• Schwarzschild radius:
10-15 m
S. W. Hawking, Nature, 248, 31 (1974)
~ size of hydrogen nucleus
p0, p-, p+
e-, e+ T ~ (1013gram/M) [GeV]
g-ray
burst
form
PBHs
Sensitivity to PBHs
Cherenkov Signal of GeV bursts
Krennrich, Le Bohec & Weekes, ApJ, 529,
506 (2000)
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0.1 – 10 ms burst profile:
 long Cherenkov pulse
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Imaging:
 characteristic shape
 extremely smooth
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No parallax:
 VERITAS
SGARFACE-II & VERITAS:
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Burst trigger in one or
several telescopes
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FADC system allows
recording of slow pulses
Sensitivity of SGARFACE
100 ns burst of 250
MeV g-rays
Min. photon density:
~ 0.2 g’s/m2
SGARFACE I:
VME-BUS
SGARFACE I:
Trigger level 1 VME-board
(16 XILINX FPGAs)
Complete system
of 64 channels
Trigger & Data
Acquisition 1
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FADC system provides
time samples with 20 ns
resolution
Trigger Logic based on
XILINX FPGAs
 reprogrammable
Runs on 5 different time
scales 50 ns – 5000 ns
Readout: 20 ns – 0.5 ms
recorded Cherenkov pulse
(June 20 2002)
125 p.e.
[d.c.]
1.4 ms
6 ms
125 p.e.
50 ns
VERITAS:
Very Energetic Radiation
Imaging Telescope Array System
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50 GeV – 50 TeV
Area:
2
= 100,000 m (1 TeV)
2
= 40,000 m (300 GeV)
2
= 1,000 m
(50 GeV)
Ang. Res.: 0.03 – 0.14 deg.
Energy resolution: 10-18%
Observation strategy:
pointed exposures
DESIGN
7-telescope Array
11m Reflectors
500 PMT
Cameras
3.5o FOV
Arrays of Imaging Telescopes I
VERITAS
- 50 GeV – 50 TeV
- Dq/q ~ 0.03o @1TeV
~ 0.09o @100GeV
- Flux sensitivity:
15 mCrab @100GeV
5 mCrab @300GeV
80 m
CAMERA
PMT Installation
Camera Box Construction
Cabling inside
FRONT-END
PMT Assembly
Amplifiers
Current Monitoring
Point Source Sensitivity
Stacee
VERITAS
HESS
Cangaroo III
MAGIC
Summary:
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TeV blazars:
 probing blazar models
 EHE cosmic-rays?
 cosmology of IR background attenuation
Many other science subjects:
 Supernova remnants, GRBs, pulsars, plerions, EGRET unident. sources, etc., …
 PBHs, dark matter searches, cosmic-ray composition,
SGARFACE I+II (exploratory):
 Sensitivity to ms bursts of GeV g-rays
 primordial black holes, pulsars (GPs), GRBs, etc.
 next generation wide field of view IACT  GRBs
VERITAS:
 20 times more sensitive than Whipple telescope
 overlap in energy with GLAST: 20 MeV – 50 TeV
 GLAST+STACEE+VERITAS+AUGER+ICECUBE+OWL
probe the universe in HE-, VHE-g-rays, C.R.’s, n’s
Future IACTs: wide field of view, 5@5GeV, photodetectors?