1. Marco Salvati INAF (Istituto Nazionale di Astrofisica)
Osservatorio Astrofisico di Arcetri
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2. TeV observatories and the IR cosmic background
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Several slides contributed by Angelo Antonelli & Alessandro De Angelis 2

3. Satellite vs. Ground-based
secondary detection (atm showers)
huge effective area
low cost
higher energy
higher bkg
Satellite
small effective area ~1m2
large duty-cycle
primary detection
large cost
lower energy
low bkg
Cherenkov
Low duty-cycle
Small FoV
High sensitivity
Low threshold
EAS detectors
High duty-cycle
Large FoV
Low sensitivity
High threshold 3

4. Observation Technique
Gamma-ray
~ 10 km
Particle
shower
~ 1o
Cherenkov light
~ 120 m
Teramo, 07 Maggio 2008
L.A. Antonelli - MAGIC & CTA

7. Teramo, 07 Maggio 2008
L.A. Antonelli - MAGIC & CTA

8. Origin of  rays  (eV-keV)‏  (TeV)‏  (eV)‏ e.m. processes
e- (TeV)‏
Synchrotron
 (eV-keV)‏
 (TeV)
Inverse Compton
 (eV)‏ B
e.m. processes
From non thermal extreme dynamic processes: - 0 +
 (TeV)‏
p+ (>>TeV)‏
matter
hadronic cascades
E2 dN/dE
energy E IC
In the VHE region,
dN/dE ~ E- (: spectral index)‏
To distinguish between had/leptonic origin
study Spectral Energy Distribution (SED):
(differential flux) . E2
0decay
VHE
SSC: a (minimal) standard model, explains most observations

9. (gamma-gamma to electron- positron conversion)
...don’t forget opacity
(gamma-gamma to electron- positron conversion)
and efficiency-suppressing mechanisms
(Klein-Nishina threshold)
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10. Science withTeV Astronomy
SNRs
Pulsars
and PWN
Micro quasars
X-ray binaries
AGNs
GRBs
Origin of
cosmic rays
Space-time
& relativity
Dark matter
Cosmology 10

11. SNR J1713.7

14. LS I

15. Unpointed measurements in 2008
Spectral features in the (e+ + e-) spectrum
possible excess around 600 GeV reported by ATIC
spectral cutoff measured by H.E.S.S. around 1 TeV
Pamela reports an increase in the positron fraction
More than 200 papers in the last year
Local source of electrons – astrophysical? Dark Matter?
Astrophysics High Energy Physics 15

16. Some possible interpretations
Several papers already published to explain electron spectrum
Together with other observations (positron fraction, diffuse -ray)‏
Pulsars
Grasso et al. 2009
Dark Matter
Strumia et al. 2009
57 citations so far, ~ > 1/day
Several sources…
Grasso et al. 2009
Secondary CR acc.
Blasi 2009 16

17. Fermi-LAT Cosmic-Ray Electron Spectrum
A. A. Abdo et al. Fermi LAT Collaboration Phys. Rev. Lett. 102, (2009) – Published May 04, 2009
(arXiv: )‏ 17

18. Adding candidate pulsars within 1kpc
arXiv:
Fermi data are nicely reproduced, assuming for each pulsar a 40% efficiency in converting spin-down energy into electrons and positrons
Pulsars are modeled as point-like, bursting sources, with a power-law injection spectrum (index=1.7) with exponential cutoff at 1 TeV 18

19. works for Pamela too arXiv:0905.0636
The presence of primary sources of positrons permits to reproduce the rising positron/electron ratio 19

20. We see high energy CR in SNR (almost up to the “knee”), and we see positrons being injected by pulsars; however, we are not sure yet about high energy protons
No evidence of dark matter annihilation products, either in local CR or in nearby dark matter clumps (Milky Way center, dwarf galaxies...)
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23. MAGIC discovery of 3C279 Teramo, 07 Maggio 2008
L.A. Antonelli - MAGIC & CTA 23

24. They explain the low gamma-gamma opacity, and the rapid variability
Why jets are important ?
They explain the low gamma-gamma opacity, and the rapid variability
There are, however, AGN with misaligned jets, and also non-jetted galaxies (these must be a collection of star-sized sources)
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25. Quantum Gravity
The energy scale at which gravity is expected to behave as a quantum theory is the Planck Mass MP = O(1.2 x 1019) GeV; at the Planck length, space should become corrugated
A consequence of these fluctuations is the fact that the speed of light in vacuum becomes energy dependent.

26. Rapid variability MAGIC, Mkn 501 Doubling time ~ 2 min H.E.S.S.
astro-ph/
arXiv:
HESS PKS 2155
z = 0.116
July 2006
Peak flux ~15 x Crab
~50 x average
Doubling times
1-3 min
RBH/c ~ s
H.E.S.S.
arXiV:

27. Violation of the Lorentz Invariance
Violation of the Lorentz Invariance? Light dispersion expected in some QG models, but interesting “per-se”
V = c [1 +-  (E/Es1) – 2 (E/Es2)2 +- …]
TeV
TeV
TeV
TeV
1st order
Es1
MAGIC Mkn 501, PLB08
Es1 ~ 0.03 MP
Es1 > 0.02 MP
HESS PKS 2155, PRL08
Es1 > 0.06 MP
GRB X-ray limits:
Es1 > 0.11 MP (Fermi, but…)
anyway in most scenarios
t ~ (E/Es), >1
 VHE gamma rays are the probe
 Mrk 501: Es2 > MP , =2
> 1 GeV
< 5 MeV
4 min lag

28. LIV in Fermi vs. MAGIC+HESS
GRB080916C at z~4.2 : 13.2 GeV photon detected by Fermi 16.5 s after GBM trigger. At 1st order
The MAGIC result for Mkn501 at z= is t = ( ) s/GeV; for HESS at z~0.116, according to Ellis et al., Feb 09, t = ( ) s/GeV
t ~ (0.43 ± 0.19) K(z) s/GeV
Extrapolating, you get from Fermi ( ) s (J. Ellis et al., Feb 2009)‏
SURPRISINGLY CONSISTENT:
DIFFERENT ENERGY RANGE
DIFFERENT DISTANCE ~z
Es1

29. Interpretation of the results on rapid variability
The most likely interpretation is that the delay is due to physics at the source
By the way, a puzzle for astrophysicists
However
We are sensitive to effects at the Planck mass scale (if 1st order)
2nd order effects?
More observations of flares
will clarify the situation

32. Are our AGN observations consistent with theory?
Selection bias?
New physics ?
Selection bias?
New physics?
adapted from De Angelis, Mansutti,
Persic, Roncadelli MNRAS 2009
Measured spectra affected by attenuation in the EBL:
observed spectral index
~ E-2
redshift
The most distant: MAGIC 3C 279 (z=0.54)‏

35. slope ~ -1 (curving downwards) maximum ~ 0.21 at ~ 0.89
wavelength of maximum ~ 1.34 mu
at E_gamma = 1 TeV
( 1340 Angstrom at E_gamma = 100 GeV)
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38. integration over redshift: if the EBL is produced entirely at high z,
the EBL photon density scales as (1+z)^3
the target frequency scales as (1+z)^-2
and the relevant distance (i.e., the light
travel time distance) scales as (1+z)
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39. 4

41. 3C279

42. Will we ever detect a Gamma Ray Burst ?
Intrinsic spectrum uncertain, typically at large distances... Up to now, however, we have systematically missed the really good ones
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44. Cherenkov Telescope Array
The future ?
CTA
Cherenkov Telescope Array
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