Astroparticle physics
with high-energy photons
I – The physics
Alessandro de Angelis
Lisboa 2006
http://www.fisica.uniud.it/~deangeli
2
The starting point


Physics constructs models explaining Nature (or better our
observations of Nature, or better observations of our
interactions with Nature)
We know Nature mostly through our eyes, which are
sensitive to a narrow band of wavelengths centered on the
emission wavelength of the Sun
3
We see only partly what surrounds us


We see only a narrow band of colors, from red to purple in
the rainbow
Also the colors we don’t see have names familiar to us: we
listen to the radio, we heat food in the microwave, we take
pictures of our bones through X-rays…
4
What about the rest ?

What could happen if we would see only, say, green color?
The universe we
don’t see



When we take a picture we
capture light
(a telescope image comes as
well from visible light)
In the same way we can map
into false colors the image
from a “X-ray telescope”
Elaborating the information is
crucial
5
Many sources radiate over
a wide range of wavelengths
6
7
And they can look
different
g (MAGIC)
We think there’s something important
we don’t see
8
velocity v
radius r
Gravity:
G M(r)/r2 = v2/r
enclosed mass:
M(r) = v2 r / G
Luminous stars only small fraction of mass of galaxy
9
The high-energy spectrum
Eg > 30 keV (l ~ 0.4 A, n ~ 7 109 GHz)
Although arbitrary, this limit reflects astrophysical and
experimental facts:



Thermal emission -> nonthermal emission
Problems to concentrate photons (-> telescopes radically
different from larger wavelengths)
Large background from cosmic particles
The subject of these lectures…
(definition of terms)

10
Detection of high-energy photons from space

High-E X/g: probably the most interesting part of the spectrum for
astroparticle

What are X and gamma rays ? Arbitrary !
(Weekles 1988)
X
X/low E g
1 keV-1 MeV
1 MeV-10 MeV
medium
10-30 MeV
HE
30 MeV-30 GeV
VHE
30 GeV-30 TeV
UHE
30 TeV-30 PeV
EHE
above 30 PeV
No upper limit, apart from low flux (at 30 PeV, we expect ~ 1 g/km2/day)
11
Outline of these lectures
0) Introduction & definition of terms
1) Motivations for the study high-energy photons
2) Historical milestones for observations
3) X/g detection and some of the present & past detectors
4) Future detectors
12
1) Motivations for the study of X/g

Probe the most energetic phenomena occurring in nature

Nonthermal

Nuclear de-excitation/disintegration

Electron interactions w/ matter, magnetic & photon fields

Matter/antimatter ann.

Decay of unstable
particles

Clear signatures
from new physics
13
Motivations (cont’d)
Penetrating

No deflection from magnetic fields, point ~ to the sources

Magnetic field in the galaxy: ~ 1mG
R (pc) = 0.01p (TeV) / B (mG)
=> for p of 300 PeV @ GC the directional information is lost

Large mean free path

Regions otherwise opaque can be transparent to X/g

Good detection efficiency
Large mean free path…
Nearest Galaxies
14
Transparency of the Universe
Nearest Stars
450 kpc
Nearest Galaxy Clusters
4.5 pc
150 Mpc
Milky Way
‘GZK cutoff’
15
HE cosmic rays
Interaction with background g
( infrared and 2.7K CMBR)
p g  N
Sources uniform
in universe
100 Mpc
10 Mpc
HE gamma rays
Mrk 501 120Mpc
g g  e+ e
Milky Way
Mrk 421 120Mpc
16
Transparency of the atmosphere
17
PHYSICS GOALS
Pulsars
GRBs
AGNs
VHM
particles
Anomalous
events
Cold Dark
Matter
SNRs
New
g-ray
Photon
propagationInvariance of c
Backg.
Acceleration mechanisms and
the origin of cosmic rays



18
Energetic protons and electrons in the vicinity of
astrophysical objects might produce gammas
Synchrotron radiation by electrons in magnetic fields could
be boosted to TeV energies by inverse Compton scattering
If acceleration mechanisms involve hadronic interactions,
there are many 0 -> gg (& the g give a clear signature)

But: neutrinos would be the “smoking gun…”
19
Active galaxies



Many sources, mostly classified
according to observational criteria
Unified AGN model (Begelman et
al. 1984): 10% of the accreted
mass is transformed into radiation
Different models predict
different g spectra
20
Pulsars

Rapidly rotating neutron stars
with

T between ~1ms and ~1s

Strong magnetic fields (~100 MT)

Mass ~ 3 solar masses


Crab pulsar
R ~ 10 Km (densest stable object
known)
For the pulsars emitting TeV
gammas, such an emission seems
unpulsed
X-ray image (Chandra)
21
g-ray bursts (History, I)

An intriguing puzzle of today’s
astronomy… A brief history

Beginning of the ‘60s: Soviets
are ahead in the space war



1959: USSR sends a satellite to
impact on the moon
1961: USSR sends in space the
27-years old Yuri Gagarin
1963: the US Air Force launches
the 2 Vela satellites to spy if
the Soviets are doing nuclear
tests in space or on the moon

Equipped with NaI (Tl)
scintillators
22
g-ray bursts (History, II)

1967 : an anomalous emission of X and g
rays is observed. For a few seconds, it
outshines all the g sources in the
Universe put together. Then it
disappears completely. Another in 1969...
After careful studies (!), origination
from Soviet experiments is ruled out



The bursts don’t come from the vicinity
of the Earth
1973 (!) : The observation is reported to
the world
Now we have seen hundreds of gamma
ray bursts...
23
g-ray bursts: why they are important

They might represent
objects near the edge of
the observable Universe

The energy could be 1015
times larger than the
energy from a supernova



E ~ 1045 J
Origin of cosmic rays?
They could be a new
observational tool for
cosmologists
g-ray bursts: what we know
and what we’d like to know

They come from every
direction in the sky


Frequently no optical emission
(BeppoSAX 1997)



Far away from the galaxy
A puzzle…
Time duration is wildly variable


Mostly extragalactic
Afterglows after > 1h…
Several mechanisms proposed,
enormous energies: a great
chance that they’re so far...
24
25
Probability of bursts

Present estimate: 1
GRB/100My/Milky Way
Galaxy
=> Already ~ 100 GRB in our
galaxy


Energy ~ 1045 J
According to Dar, it is not
unlikely that a GRB has
already interacted with the
atmosphere…
Importance of the multiwavelength
approach
26
27
The “standard model”

Many sources can be related to
SN remnants




Mechanism accounting for repeated
shocks (Dar, De Rujula)
Matter of precise poninting:
Work for GLAST
Synergy with gravitational wave
detectors
Work for LIGO
But: Maybe different kinds of
bursts…
The key observation are
for the period 2005-2010

December 04: Swift (X-ray
up to 150 keV, >1 GRB/day,
link with Cherenkov)

MAGIC: 1 to 10 useful
alerts/year


Already 2 happended in one
year…
GLAST
2nd half 2007:
GLAST (30 MeV to 300
GeV)
MAGIC
28
29
GRBs for cosmology?
Ghirlanda et al. (2004)
GRB standard candle constructed
from the Ghirlanda et al. power-law
relation between the geometrycorrected energy and the peak of
the rest-frame prompt burst
spectrum (E_p)
30
g propagation


Quantum gravity (Amelino-Camelia
et al., Ellis et al.)
V = c (1 - e E/EQG)
Effects on GRB could be O(100 ms)
Due to gg -> e+e-, CMB and visible
light absorb g at the PeV and at
the TeV

At the GKZ cutoff (1020 eV) the
Universe regains transparency to g
The transparency of the Universe
gives insights on the infrared/
optical diffuse background
31
=> Intergalactic g absorption




Photons interact with the IR
background => relationship
source distance / maximum
observed photon energy
Measurement from the
distortion of AGN spectra
Data in the range 50 GeV - 300
GeV would be crucial
And an important byproduct:
the best constraints on Lorentz
violation, photon oscillations etc.
Lorentz gamma: 10^5 -> 10^10
Conversely, if you would know the IBL..
GRH depends on g–ray path which depends on cosmological parameters
dl
1 / 1  z 
 c
dz
H0  M 1  z 3  k 1  z 2   l

 assuming EBL is know

1/ 2
=> determine cosmolog. parameters
l
 use foreseen precision of GRH
measurements
 assume H0 known
 determine M and l
 2-parameter contour improves by
factor 2 present Supernova combined
result (astro-ph/0107582)
 method is complementary and
independent from supernova 1a
measurements
But… systematic errors
M
32
33
g propagation: sensitive also to exotics

Violation of the Lorentz symmetry


S.Coleman and S.Glashow, PLB405 (1997) 249
Extra photons


S.Glashow, PLB430 (1998)
The photon/paraphoton transition could mimic the distortion in the light spectrum
from far Type Ia SuperNovae (A. De Angelis and R. Pain, MPLA17 (2002) 2491)
Cosmic Rays
The future of HEP?

Today’s accelerator physics
limited & many early
discoveries in particle physics
came from the study of
cosmic rays


34
Motivation for particle
physicists to join
Higher energies are not the
full story…
Also small x (lost in the beam
pipes for collider detectors)
35
Particle Acceleration
Large Hadron Collider
E  BR
R  10 km, B  10 T
 E  10 TeV
Tycho SuperNova Remnant
R  1015km, B  1010T  E  1000 TeV
( NB. E  Z  Pb/Fe higher energy)
36
Particle Physics
 Particle Astrophysics
Energy of accelerated particles
Active Galactic Nuclei
Binary Systems
SuperNova
Remnant
LHC CERN, Geneva, 2007
Cyclotron Berkeley 1937
37
Dark Matter Searches


Evidence from observational
cosmology that one quarter of
the Universe consists of Cold
Dark Matter (CDM≈0.23)
Weakly Interacting Massive
Particles (WIMPs) favored.


Direct Searches: detect collision with ordinary matter in
underground experiments (DAMA, GENIUS, CDMS, CRESST, …)
Indirect Searches: detect annihilation products: anti-p, e+, n, g
[AMS, ANTARES, AMANDA (IceCube), GLAST, MAGIC, HESS,
VERITAS, CANGAROO, …]
38
DM Candidates
M > ~ 40 GeV
if SUSY (LEP)
39
“Standard” candidate: Neutralino


in case of R-parity conservation lightest Super Symmetric
particle (LSP) is stable
neutralino : attractive candidate for the LSP
only weak cross-section: attractive Cold Dark Matter
candidate

neutralino: Majorana Fermion  self-annihilation

expected mass range: 100 GeV < m < 1 TeV
(limits from WMAP, LEP in framework of constrained SUSY models)
40
Neutralino annihilation

annihilation


into gg or gZ:
Eg = m / m mZ2/4 m
=> clear signature at high
energies
but: loop suppressed

± , W
g,Z
Good energy resolution in
the few % range is needed
g
annihilation into qq -> jets -> n g’s
=> continuum of low energy gammas
difficult signature but large flux

q

q
41
g-Flux from -Annihilation
dNg (, E )

2



DM (l ) dl ()
2

dtdAdEd 
M

Particle physics:
SUSY models
fragmentation functions
Prada, Flix, et al: astro-ph/0401512
pMSSM

Astrophysics:
g-ray flux ~ 2
=> search for CDM clumps
42
Backgrounds
 CR hadrons
reduced by image
analysis, O(0.01)
 CR electrons
no reduction possible
 diffuse galactic gs
from CR interactions
with galactic matter
(main background
for satellites)
m=150 GeV
m=800 GeV
m=1.5 TeV
 extragalactic photons
(AGNs, cosmological
neutralinos)
 improved background
rejection for pointlike
sources
experiments sensitive to Egγ > Eth (M > Eth)
43
DM density profiles: Cusp, Core, Clumps…


gamma-flux dependence 2 => inner, high DM region dominating
N-body CDM simulations:
uncertainties mainly due to
extrapolation to r<rsim
3
rs 
r
(r)  o  1 
r 
rs 




Navarro,Frenk & White (1996):
NFW = 1
Moore (1998):
Moore = 1.5
Stoehr (2004)
 < 1
experimental data for GC (rotation
curves, microlensing data, ..)
 no evidence for cuspy profile
 cusp not unambiguously ruled out
predictions for ∫2(l)dl
differ by orders of
magnitude
Possible AP effects
enhance DM density
Common sense suggests a look @the GC…
M= 3.6 x 106
Solar Masses
LIP
Annihilation radiation from the GC
44
45
g-ray detection from the Galactic Center
-7


detection of g-rays from GC by Cangaroo,
Whipple, HESS, MAGIC
source < 3’ ( < 7 pc at GC)


E2 dN/dE
10
-8
10
hard E-2.21±0.09 spectrum
fit to -annihilation continuum
spectrum leads to: M > 12 TeV
15 TeV
WIMP
6 TeV
WIMP
other interpretations possible (probable)
Galactic Center: very crowded sky region, strong
exp. evidence against cuspy profile
-9
10
0,1
Chandra GC survey
NASA/UMass/D.Wang et al.
CANGAROO (80%)
H.E.S.S.
Whipple
(95%)
astro-ph/0408145
from W.Hofmann, Heidelberg 2004
1
10
Energy [TeV]
Milky Way satellites
Sagittarius and Draco
 proximity (< 100 kpc)
low baryonic content,
no central BH (which may
change the DM cusp)


large M/L ratio
46
No clear information
about the shape
Point-like core
TeV
Extended tail
H.E.S.S.
47
GC observed in VHE gamma by Cangaroo, HESS, MAGIC
• HESS+MAGIC and Cangaroo results don’t match
Cangaroo spectral index
Γ=-4.6±0.5
E2 dN/dE
HESS spectral index
Γ=-2.63±0.04
MAGIC 2005: Γ=-2.3±0.4
flux: ~10% of Crab
no apparent variability
10-7
10-8
10-90,1
HESS, astro-ph/0408145
6 TeV
WIMP
15 TeV
WIMP
1
10
Energy [TeV]
Conclusions on the signal from the GC
[the market for (astro)phenomenologists]

A gamma signal ~ 20 TeV from the GC, constant in time
It is not likely to be DM, but needs more investigation
Conclusion on DM Search


Next years (2006-2008) will be the gamma-rays years
(sensitivity is increasing 100x in the 100-GeV region)
Plans for observations by MAGIC & HESS next years, also
by gambling…
48
49
New Matter or New Physics?
In the past, deviations from Newton’s law found different
explanations
Uranus, Neptune, etc.
Mercury
Need non-gravitational evidence
“DARK” PLANETS
REFINED LAWS OF
GRAVITATION
50
Anomalous events

Anomalous showers at UHE (> 7 PeV)
from Cygnus X-3 (Samorski & al. 1983):
almost no photons…

Increasing total photon X-section
due to virtual gluons



Increasing neutrino X-section

New particles
Anomalous events (highly penetrating
hadrons)
Normally killed as “irreproducible
results”, but…
Study of exotic objects:
other phenomena


Top-Down : Decay of massive cosmic strings
(1015 GeV, Kolb & Turner 1990)
Unknown transients

Time resolution is the key
51
52
2) Historical milestones
for observations
1952 Prediction of He X/g high energy emission (Hayakawa)
1957 Sputnik 1
1958 Inventory of cosmic sites expected to radiate in the
X/g (Morrison)
1968 (11 years after the Sputnik): X emission of the galaxy
1972 g from Crab Nebula
1973 First report on gamma ray bursts
1978 Gamma-ray spectroscopy : e+e- annihilations @ the GC
1983 Nuclear processes at the GC
53
Some selected results
54
X/g Satellites in the ’90s



GRANAT (SIGMA), 1990/97

Accreting black holes

Jets
CGRO, 1991/2000

BATSE, thousands of GRB

EGRET, hundreds of GRB in the HE region
BEPPO Sax, 1996/2002

SN remnants
55
Gamma satellites

EGRET [+BATSE]





Diffuse g emissions dominate the
g-ray sky. After removing the
identified point sources, ~ mass
distribution
Moreover, isotropic emission at
high latitude going like E-2.07+-0.03
Pulsars, all observed also in the
radio (apart from Geminga)
Most point sources unidentified
Gamma-Ray Bursts, not expected
in any model. No apparent E cutoff, E as high as 18 GeV
The pulsar spectrum depends
on the wavelength =>
Different energies produced
in different regions?
56
VHE sources

Observations in the ‘90s confirm earlier
detection of VHE emissions from Crab nebula
and discover new VHE sources in pulsars (PSR
1706-44, Vela)


No pulsed emission
TeV emission from AGN, with flares

Mkr 421

Mkr 501
Models differ in the kind of particles
emitted & E spectrum


Synchrotron model => 2 humps, one from
synchrotron and one from inverse Compton
Variability over a large range of timescales
Observational hole
upper limit from EGRET
Results from
ground-based
57
58
2004/2005: the era of the new IACTs

Impressive observational results by HESS in 2004-2006
and by MAGIC in 2005-2006
59
Crab energy spectrum
Measured over 20 decades
Synchrotron
MAGIC
I.C.
g (MAGIC)
X-Ray
I.R.
60
Scientific Highlights (Aug.2005)
Galactic observations:
I.
Discovery of many new Galactic sources by HESS:
•
II.
Detailed studies of Galactic sources by HESS:
•
•
III.
Precision measurements (spectra, morphology, etc.).
Theoretical models and understanding.
Discovery of new classes of VHE gamma-ray emitters by HESS and
MAGIC:
•
•
IV.
HESS GP Survey & targeted observations.
First variable galactic source
First periodic galactic source, by MAGIC
Study of the Galactic Center by CANGAROO,HESS and MAGIC:
•
Evidence for a TeV signal; search for DM annihilation
61
Scientific Highlights (Aug.2005)
Extragalactic observations:
V.
Discovery of 8 new AGN by HESS and MAGIC:
•
•
VI.
Observation of AGN with orphan flares by MAGIC:
•
VII.
Connexion to neutrino and UHECR astronomy?
High time-resolution study of AGN flares by MAGIC:
•
VIII.
Measurements of AGN properties and multi-l studies.
Constraints on cosmological EBL density from absorption spectrum.
New constraints on emission mechanisms and light speed dispersion relations.
Prompt GRB follow-up by MAGIC:
•
GRB follow-up in coincidence with observation in the X-ray domain.
62
HESS Galactic Plane Survey
RXJ 1713
MSH 15-52
RXJ 0852
Survey
Region
GC
Vela X
PSR B1259
HESS J1303
•
•
60° in longitude,  3° in latitude
112 hrs scanning + follow-up observations
HESS Galactic Plane Survey
63
Sources > 6 sigma:
9 new, 11 total
Sources > 4 sigma:
7 new
330°
H.E.S.S. Highlight:
Resolved Supernova Remnants
RX J1713-3946
64
65
Spectra
Preliminary
 Acceleration of
primary particles
in SNR shock to
well beyond 100 TeV
Index ~ 2.1 – 2.2
Little variation
across SNR
Cutoff or break at
high energy
Binary Pulsar PSR B1259-63
first variable galactic TeV source
HESS
J1303-631
PSR
B1259-63
Feb. 04
early March 04
Apr./May 04
66
67
Extragalactic
Spectral Index
2.9
2.2
2.4
2.9
2.4
4.0
3.3
3.3
3.1
3.0
2.9
4.0
Type
FR I
4.5
BL Lac
4.0Lac
BL
BL Lac
3.5
BL Lac
BL
3.0Lac
BL Lac
2.5Lac
BL
BL
Lac
2.0
BL Lac
1.5Lac
BL
0
BL Lac
Spectral Index
Source
Redshift
M87
0.004
Mkn 421
0.031
Mkn 501
0.034
1ES 2344+514
0.044
1ES 1959+650
0.047
PKS 2005-489
0.071
PKS 2155-304
0.116
H1426+428
0.129
H2356-309
0.165
1ES 1218+304
0.182
1ES 1101-232
0.186
PG 1553
>0.25
BLFirst
Lac objects
Confimation
Detection
HEGRA
PKS2005
Whipple
Whipple
Whipple
Tel. Array
HESS
Mark VI
Whipple
HESS
MAGIC
HESS
0.1
HESS
HESS
PG1553
Many
Many
HEGRA,MAGI
C
Many
HESS
Many
0.2
0.3
MAGIC
Redshift Parameter z
At least a handle on EBL, but also the possibility of accessing cosmological
constants (Martinez et al.) could become reality soon (maybe including X-ray
obs.)
0.4
68
Extragalactic Background Light (EBL)



Cosmological radiation from star formation and evolution.
Spectral signature from gg absorption for Eg ~ 50-2000 GeV.
Use measured AGN spectra to constrain EBL.
Source
EBL spectrum
G = 1.5
1 ES 1101
G = 2.9±0.2
preliminary
H 2356 (x 0.1)
G = 3.1±0.2
Preliminary
69
GRH measurement is constraining the
EBL density and…
Blanch & Martinez 2004
Different
EBL models
Simulated
measurements
Mkn 421
Mkn 501
1ES1959+650
PKS2005-489
PKS 2155-304
H1426+428
H2356-309
1ES1218+304
1ES1101-232
70
… paving the way for the use of AGNs
to fit M and  …
Blanch & Martinez 2004
PKS 2155-304 H2356-309
PKS2005-489 H1426+428
1ES1218+304
1ES1959+650
1ES1101-232
Mkn 421
Mkn 501
Simulated
measurements
71
AGN with orphan flares
• Source observed already by Whipple
and HEGRA in flaring state.
• Orphan flares (hadronic origin ?)
• MAGIC observation
• Two neutrinos in AMANDA data ?.
Unconfirmed
• Two HiRes stereo events ?.
=> Connexion between Gamma-ray
astrophysics and neutrino/UHECR
astrophysics ?
72
Tests of Quantum Gravity effects

From a phenomenological point of view, the effect can be studied
with a perturbative expansion. In first order, the arrival delay of
grays emitted simultaneously from a distant source should be
proportional to their energy difference and the path L to the
source:
E L
t 
EQG c

The expected delay is very small and to make it measurable one
needs to observe very high energy g-rays coming from sources at
cosmological distances.
73
High time-resolution study of AGN flare
Preliminary
• Huge Mkn 501 flare on
Crab
1st July 2005 -> 4 Crab
intensity.
• Intensity variation in 2
minute bins -> new, much
stronger, constraints on
emission mechanism and
light-speed dispersion
relations (effective
quantum gravity scale).
Preliminary
2 minutes time bins
GRB Observation


MAGIC is the right instruments, due
to its fast movement & low threshold

MAGIC is in the GCN Network

GRB alert active since Apr 2005

8 useful triggers since
For the first time with a useful
sensitivity MAGIC observed a GRB at
high-energy symultaneously with the
primary burst (for 30s)

GRB050713a (threshold of 120 GeV)

GRB050904 (threshold of 60 GeV)
74
Gamma Ray Bursts
#
GRB Event
75
Satellite
Onset
[UTC]
t alert
[sec]
t obs.
[sec]
q
deg]
z
1.23
1
GRB050408
HETE
16:22:50
14
3138
48
2
GRB050421
SWIFT
04:11:52
58
112
52
3
GRB050502
SWIFT
02:14:18
18
990
33
3.79
4
GRB050505
SWIFT
23:22:21
540
793
50
4.27
5
GRB050509A
SWIFT
01:46:29
16
115
57
6
GRB050509B
SWIFT
04:00:19
15
368
69
7
GRB050528
SWIFT
04:06:45
43
77
52
8
GRB050713A
GRB050713A
SWIFT
04:29:02
04:29:02
13
40
49
• On 13 July 2005 MAGIC
has observed a GRB with
only 40 s delay
• Preliminary analysis
shows no signal > 175
GeV
• Constrain models on
prompt emission
0.23
76
A comment


Very special moment in VHE Cosmic gamma-ray observation:
real revolution in consolidation of Cherenkov telescopes as astronomical
instruments
=> transition from “HE experiments” to “telescopic installations”
--> exploding interest in the astronomical community… !
Big observational step within the last year:
- quantitative (tripling number of detected sources)
- qualitative (extremely high quality => unprecedented detailed studies).
=> GOLDEN AGE FOR CHERENKOV TELESCOPES !
And new detectors (satellite-based, wide-field) will become operative soon
77
Summary of the results




The new generation of Cherenkov telescopes is yielding outstanding
results
VHE gamma-ray installations are establishing themselves as
astronomical observatories: VHE gamma-ray astrophysics is now
emerging as a solid new astronomy.
More new VHE sources discovered in the last year than in the last 20
years… and likely many more coming !
Implications on fundamental physics are clear, especially in the sectors
of




DM
Lorentz violation
Cosmological parameters
…
The progress at a glance
The next years: surveys of VHE/UHE?
South/North ~ 3/2
78
79
Sensitivity
Survey: ~0.1 Crab
Pointing: ~0.01 Crab
And the next future of high-sensitivity
installations

If financed (cost >~ 100 MEUR)
80
81
Summary

High energy photons (often traveling through
large distances) are a great probe of physics under extreme conditions


Observation of X/g rays gives an exciting view of the HE universe




Many sources, often unknown
Diffuse emission
Gamma Ray Bursts
No clear sources above ~ 50 TeV


What better than a crash test to break a theory ?
Do they exist or is this just a technological limit ?
We are just starting… Next lecture: many new detectors being built or
planned
Future detectors: have observational capabilities to give SURPRISES !