Post on 19-Jul-2020
1/81
Alessandro De Angelis, INFN/INAF Trieste, U. Udine & IST/LIP Sesimbra 09
Gamma Astro(particle)Physics:
1 – The detectors and our new view of the sky
2/81
The universe we don’t see
Some of the characteristics of the Universe appear only when we can take a multiwavelength picture
For each band, it is important to
Have the right instrumentBe able to process the information
X ray maps are less than 50 yrs old; gamma-ray maps are less than 20 yrs old
3/81
Many sources radiate over a wide range of wavelengths
4/81
And the key to understand the underlying physical processesmight not be in the visible band
γ (MAGIC)
Crab Nebula(SN 1054)
5/81
We know there’s something very important we don’t see
Gravity:G M(r)/r2 = v2/renclosed mass: M(r) = v2 r / G
velocity vradius r
Luminous mass only a fraction of the mass of the Universe
6/81
(V)HE gamma rays
γ: probably the most interesting part of the spectrumNonthermal, key to access fundamental processesBut… Experimentally difficult:
One cannot concentrate photonsHuge background (2-3 orders of magnitude larger) from charged CR
What are gamma rays ? Arbitrary ! (Weekles 1988)
low-medium E γ 500 keV-30 MeV
HE 30 MeV-30 GeVVHE 30 GeV-30 TeVUHE 30 TeV-30 PeVEHE above 30 PeVNo upper limit, apart from low flux
(at 30 PeV, we expect < 1 γ / km2/day)
7/81
Motivations for the study of (V)HE gammas
Large mean free pathRegions otherwise opaque can be transparent to X/γ
No deflection from magnetic fields, point ~ to the sources
Magnetic field in the galaxy: ~ 1μGR (pc) = 0.01p (TeV) / B (μG)=> for p of 300 PeV @ GC the directional information is lost
Key to cosmic rays:for reasonable mechanisms of hadron production at energy E, γ of energy ~ E/10Key to fundamental physics
Last but not least, recently we have learned how to detect them
8/81
eVGeV500at peaking
by limited
⎟⎟⎠
⎞⎜⎜⎝
⎛=
→ −+
B
Bγ
γ
B
EE
eeγγLarge mean free path…Universe transparency
4.5 pc
450 kpc
150 Mpc
Nearest Stars
Nearest Galaxies
Nearest Galaxy Clusters
Milky Way
1 TeV
1 PeV
9/81
Transparency of the atmosphere
10/81
Consequences on the techniques
The fluxes of h.e. γ are low and decrease rapidly with energy
Vela, the strongest γ source in the sky, has a flux above 100 MeV of 1.3 10-5
photons/(cm2s), falling with ~E-2 => a 1m2 detector would detect only 1
photon/2h above 10 GeV
=> with the present space technology, VHE and UHE gammas can
be detected only from atmospheric showers
Ground-based detectors, atmospheric shower satellites
The flux from high energy cosmic rays is much larger
The earth atmosphere (28 X0 at sea
level) is opaque to X/γ => only sat-
based detectors can detect
primary X/γ
11/81
Satellite-based and ground-based: complementary, w/ moving boundaries
Flux of diffuse extra-galactic photons
Ground-based
Sat
12/81
E [MeV]210 310 410 510 610 710
]
−1 s
−2d
N/d
E [
erg
cm
2E
−1210
−1110
−1010
PRELIMINARY
Only since 2008 we are closing the gap!
Synchro
ComptonCrabNebula
PRELIMINARY
CrabPulsar
Mkn 421
Fermi
MAGICFermi MAGIC
VeritasHESS
Fermi 100 days
MAGIC 27 hours
13/81
Ground-based vs Satellite
Satellite:primary detectionsmall effective area ~1m2
lower sensitivitylarge duty-cyclelarge costlower energylow bkg
Ground basedsecondary detection huge effective area ~104 m2
Higher sensitivitysmall angular openingsmall duty-cyclelow costhigh energyhigh bkg
14/81
Satellite-based detectors:figures of merit
Effective area, or equivalent area for the detection of γAeff(E) = A x eff.
Angular resolution, important for identifying the γsources and for reducing the diffuse background
Energy resolution
Time resolution
15/81
EGRET
High Energy γ detector 20 MeV-10 GeV
on the CGRO (1991-2000)
thin tantaliumplates with wire chambersScintillators for trigger
Energy measured by a NaI (Tl) calorimeter 8 X0 thickEffective area ~ 0.15 m2 @ 1 GeVAngular resolution ~ 1.2 deg @ 1 GeVEnergy resolution ~20% @ 1 GeV
Scientific successIncreased number of identified sources, AGN, GRB, sun flares...
16/81
The GLAST/Fermi observatory and the LAT
Large Area Telescope (LAT)Gamma Ray Burst Monitor (GBM)
Spacecraft
Rocket Delta II Launch base Kennedy Space CenterLaunch date June 2008Orbit 575 km (T ~ 95 min)
LAT Mass 3000 KgPower 650 W
Heart of the instrument is the LAT, detecting gamma conversions γ
e+ e–
TRACKER
CAL
ACD
International collaboration USA-Italy-France-Japan-Sweden(it has a small precursor: the all-Italian AGILE)
17/81
LAT overview
γ
e+ e-
Si-strip Tracker (TKR) 18 planes XY ~ 1.7 x 1.7 m2 w/ converter Single-sided Si strips 228 μm pitch, ~106
channelsMeasurement of the gamma direction
Calorimeter (CAL)Array of 1536 CsI(Tl) crystals in 8 layers
Measurement of the electron energy
AntiCoincidence Detector (ACD)89 scintillator tiles around the TKR
Reduction of the background from charged particles
Astroparticle groups INFN/University Bari, Padova, Perugia, Pisa, Roma2, Udine/Trieste
The Silicon tracker is mainly built in Italy
Italy is also responsible for the detector simulation, event display and GRB physics
18/81
The Fermi LAT outperforms EGRET by two orders of magnitude
19/8119
Launch of GLAST/Fermi (Cape Canaveral, June 2008)
20/81
Detection of a gamma-ray
21/81
Ground-based telescopesstill needed for VHE…
Peak eff. area of Fermi: 0.8 m2
From strongest flare ever recorded(*) of very high energy (VHE) γ-rays:
1 photon / m2 in 8 h above 200 GeV(PKS 2155, July 2006)
The strongest steady sources are > 1 order of magnitude weaker!
Besides: calorimeter depth ≤ 10 X0
⇒ VHE astrophysics (in the energy
region above 100 GeV) can be
done only at ground
(*) Up to November 2009…
22/81
Ground detectors: EAS and IACT
• EAS (Extensive Air Shower): detection of the charged particles in the shower
• Cherenkov detectors: (IACT): detection of the Cherenkov light from charged particles in the atmospheric showers
23/81
Extensive Air Shower Particle Detector Arrays
Largest sensitivity to UHE gammas
small flux => need for large surfaces, ~ 104 m2
But: 100 TeV => 50,000 electrons & 250,000 photons at mountain altitudes, and sampling is possible
Typical detectors are arrays of detectors with a fraction of sensitive area < 1%
Possibly a μ detector for hadron rejection
Direction from the arrival times, δθ can be ~ 1 deg
Thresholds rather large, and dependent on the point of first interaction
24/81
EAS Particle Detector ArraysPrinciple
Each module reports:Time of hit (10 ns accuracy)Number of particles crossing detector moduleTime sequence of hit detectors -> shower direction
Radial distribution of particles -> distance LTotal number of particles -> energy
25/81
Cherenkov (Č) detectorsCherenkov light from γ showers
Č light is produced by particles faster than light in air
Limiting angle cos θc ~ 1/n Threshold @ sea level : 21 MeV for e, 44 GeV for μ
θc ~ 1º
Maximum of a 1 TeV γ shower ~ 8 Km asl
200 photons/m2 in the visible
Duration ~ a few ns
Angular spread ~ 0.5º
26/81
Cherenkov detectors: principles of operation
Cherenkov light detected using mirrors which concentrate the photons into fast PMs
In the beginning, heliostats Problem: night sky background
Signal ∝ Afluctuations ~ (AτΩ)1/2
=> S/B1/2 ∝ (A/τΩ)1/2
Now, a 3rd generationSmaller integration times ~nsImproved PMsLarge areas => Low threshold Multi-telescopeClose the gap ~ 100 GeV between satellite-based & ground-based instruments
27/81
A summary of the performance
Fermi Cherenkov EAS’Energy 20MeV – 200GeV 100GeV – 50TeV 400GeV–100TeVEnergy res. 5-10% 15-25% (*) ~50%Duty Cycle 80% 15% >90%FoV 4π/5 5deg x 5deg 4π/6PSF 0.1 deg 0.07 deg 0.5 degSensitivity (**) 1% Crab (1 GeV) 1% Crab (500 GeV) 0.5 Crab (5 TeV)
(*) Decreases to 15% after cross-calibration with Fermi(**) Computed over one year for Fermi and the EAS, over 50 hours for the IACTs
28/81
Incoming γ-ray
~ 10 kmParticleshower
~ 1o
Chere
nkov
light
~ 120 m
−+→+ eepγγ→+ −+ ee
Image intensityShower energy
Image orientationShower direction
Image shapePrimary particle
Observational Technique
29/81
Better bkgd reduction Better angular resolutionBetter energy resolution
Systems of Cherenkov telescopes
30/81
VERITAS: 4 telescopes operational since 2006
H.E.S.S.: 4 telescopes operational since 2003
The VHE connection…
31/81
MAGIC
17 m
17 m
ReflRefl. . surfacesurface::236 m236 m22, F/1, 17 m , F/1, 17 m ∅∅
–– Lasers+mechanisms for AMCLasers+mechanisms for AMC
CameraCamera::~ 1 m ~ 1 m ∅∅, 3.5, 3.5°°FoVFoV
AnalogicalAnalogicalTransmissionTransmission((opticaloptical fiberfiber))
TriggerTriggerDAQ > 1 DAQ > 1 GHzGHzEventEvent rate ~300 Hzrate ~300 Hz
RapidRapid pointingpointing–– Carbon fiber structureCarbon fiber structure–– Active Mirror ControlActive Mirror Control
⇒⇒ 2020÷÷30 30 secondsseconds
32/81
MAGIC looksfarthest away: z~1.2 (wrt z~0.8Of H.E.S.S.)
Very fast movement (< 30 s)
MAGIC
2
34/81
A summary (oversimplified…)
10-14
10-13
10-12
10-11
10 100 1000 104 105
E [GeV]
Crab
10% Crab
1% Crab
Fermi
Magic2
Sen
sitiv
ity [
TeV
/cm
2 s ]
Hess/Veritas
Present EAS
(Argo, Milagro…)
35/81
Origin of γ rays from gravitational collapsesSSC: a (minimal) standard model
(0.1-1)% of energy into photons…SSC explains most observations, not necessarily the most interesting…
E2dN
/dE
energy E
IC
e- (TeV) Synchrotronγ (eV-keV)
γ (TeV) Inverse Comptonγ (eV)
B
leptonic acceleration
π0decay
π-
π0
π+
γγ (TeV)
p+ (>>TeV)
matter
hadronic acceleration
VHEIn the VHE region,dN/dE ~ E−Γ (Γ: spectral index)
36/81
Dec 2009: release of the 1st Fermi catalog above 100 MeV (1451 sources, more than half extragalactic: EGRETx5)
37/81
Day-by-day variability (> 1/3 extrag)
38/81
Millisecond variability
Pulses at1/10th true rate
39/81
94 sources (as of Dec 09)
Above 100 GeV
40/81
HESS’ galactic scan (2003-2007)
41/81
We found many new kinds of objects emitting (V)HE photons
Which physics questions can they answer?
Do emission processes continue at the highest energies?
Photons produced in hadronic cascades can be a signature of protons at an energy 10 times larger
=> Cosmic Rays
The highest energies can test fundamental physics in the most effective way
Detection of new particles (dark matter, …)
Interaction of photons with background particles in the vacuum
Tests of Lorentz invariance & other fundamental symmetries
…
42/81
Summary of the 1st lecture
In the recent few yearsGeV: thanks to the Fermi satellite the sensitivity has increased by a factor of 10
⇒ ~1000 sources > 100 MeV
TeV: thanks to Cherenkov telescopes it is now possible to make maps of the Universe
⇒ ~100 sources > 100 GeV
These cosmic accelerators are unveiling unexpected phenomena in the Universe
This progress is a textbook example of the merging of particle physics and astrophysics into the modern field of astroparticle physics
In the second lecture we’ll see that our observations can also tell us a lot about fundamental physics
43/81Alessandro De Angelis, INFN/INAF Trieste, U. Udine & IST/LIP Sesimbra 09
Gamma Astro(particle)Physics:
2 – Selected physics results (with emphasis on fundamental physics), and perspectives
44/81
Origin of γ rays from gravitational collapsesSSC: a (minimal) standard model
(0.1-1)% of energy into photons…SSC explains most observations, not necessarily the most interesting…
E2dN
/dE
energy E
IC
e- (TeV) Synchrotronγ (eV-keV)
γ (TeV) Inverse Comptonγ (eV)
B
leptonic acceleration
π0decay
π-
π0
π+
γγ (TeV)
p+ (>>TeV)
matter
hadronic acceleration
VHEIn the VHE region,dN/dE ~ E−Γ (Γ: spectral index)
45/81
Spectacular results (some 4 papers/month, some 10 per year on Nature/Science)Crab pulsation (Science, November 2008)
MAGIC detected pulsed γ-rays from the Crab above 25 GeV, revealing a relatively high energy cut-off in the pulsed spectrumFirst observation of pulsed emission at O(10 GeV), first indication of a cutoff
46/81
New kinds of emitters: pulsars, binaries, …LSI+61 303 (Science 2007)
High mass x-ray binary system at 2 kpc, composed:Be star (18 M ) & Unknown compact object: neutron star, BH?
Discovered by MAGIC in 2005/06
Visible only at some orbital phases
Periodicity test reveal: P = 26.8±0.2 days
First time a periodically variable VHE emitter was seen
=> (V)HE gamma emission is a common feature
47/81
Cosmic rays: evidence for the emission of VHE hadrons by SNR
Existence of possible mechanismsConsistent w/ energetics
Better fits to energy spectra
MorphologySeveral regions /SSCStatistics of PWNPower law consistent with powering by protons with Γ ~ 2
Up to 100 TeV → CR at O(1 PeV)
48/81
Standard Model of galactic Cosmic Rays
Galaxy is a leaky boxEnergy-dependent escape of CR from the GalaxyCR source spectra must be dN/dE = E-2.1 to -2.4 to match E-2.7 CR spectrum measured at Earth
Supernova Remnants accelerate cosmic raysAcceleration of CR in shock produced with external medium that lasts ~1000 years SN rate of 1/30 years means ~30 SNR are needed to maintain cosmic ray flux
Model explains most observations, and is consistent with many details
49/81
Starburst galaxies
Starburst galaxies exhibit in their central regions a highly increased rate of supernovae, accelerating cosmic rays
Gamma rays—tracers of such cosmic rays—have been detected
from starburst galaxy NGC253 (Fermi+HESS, Science 2009)From M82 (Fermi+VERITAS, Nature 2009)
50/81
Evidence for the emission of EHE hadrons by AGN
The “direct” measurement by AUGER (E > 60 EeV)
Orphan flares in TeV band (?)The production region of gammas from flares in M87 is very closeto the BH, where there is abundance of protons
If SNRs O(10 SM) can explain CR at O(1 PeV), BH O(109 SM) are likely to explain CR up to O(1023 eV)
27 events as of November 2007 58 events now (with Swift-BAT AGN density map)
51/81
What we are learning on CR (great results recently…)
Thanks to IACTs & Fermi, the mechanism of generation of CR up to the knee by SNR (PWN in particular) has found experimental proof
Still the “smoking gun”is missing, though
Emission by AGN is likelyγ astrophysics can study the morphology of CR emitters (mostly Galactic, but not only: M87)
VHE
X-ray
Radio
nucleus
jet
knot HST-1
nucleus
VHE flareFollowed by increase of radio flare close BH
Science, 325 (2009) 444Joint paper MAGIC-VERITAS-HESS-VLBI-Chandra
52/8152
Dark Matter )(Znqq
γγχχγχχ
→×→→
53/81
- other γ-ray sources in the FoV=> competing plausible scenarios- halo core radius: extended vs point-like
BUT:
Highest DM density candidate:Galactic Center? Close by (7.5 kpc)Not extended
DM search(Majorana WIMPs) )(Z
nqqγγχχ
γχχ→
×→→
54/81
γ-ray detection from the Galactic Center
Chandra GC surveyNASA/UMass/D.Wang et al.
CANGAROO (80%)
Whipple(95%)
H.E.S.S.
from W.Hofmann, Heidelberg 2004
detection of γ-rays from GC by Cangaroo, Whipple, HESS, MAGIC
σsource < 3’ ( < 7 pc at GC)
hard E-2.21±0.09 spectrumfit to χ-annihilation continuumspectrum leads to: Mχ > 14 TeV
other interpretations possible (probable)Galactic Center: very crowded sky region, strong
exp. evidence against cuspy profileMilky Way satellites Sagittarius, Draco, Segue, Willman1, Perseus, …
proximity (< 100 kpc)low baryonic content,
no central BH (which may change the DM cusp)
large M/L ratioNo signal for now…
no real indication of DM…
The spectrum is featurless!!!
…and satellite galaxies
55/81
Fermi: search for spectral linessmoking gun signal of dark matter
Search for lines in the 30-200 GeV energy range
Search region |b|>10 deg and > 20 deg around GC
No line detected, 95% limits placed
For each energy (WIMP mass) the flux ULs are combined with the density function to extract UL on the annihilation cross section <σv>
Limits on <σv> are too weak (by O(1) or more) to constrain a typical thermal WIMP
Some models predict large σ into lines: exg. Wino LSP (Kane 2009): γZ line, but they were disfavored by a factor of 2-5 depending on the halo profile
56/81
Study of dSph
Select most promising dSph based on proximity, stellar kinematic data: <180 kpc from the Sun, more than 30o
from the galactic plane14 dSph have been selected for this analysis. More promising targets could be discoveredVery large M/L ratio: 10 ~> 1000 (~10 for Milky Way)
57/81
Flux UL are combined with the DM density inferred by the stellar data for a subset of 8 dSph => constraints on <σv> vs WIMP mass for specific DM modelsExclusion regions already cutting into interesting parameter space for some (extreme) WIMP models
58/81
γ detection from satellite galaxiesFermi vs. MAGIC/HESS/VERITAS
Willman-I [ApJ 697 (2009) 1299]
Profumo et al:
at m~0.5-1 TeV, comparable sensitivities for Fermi vs IACTsat m>1 TeV, IACTs outperform Fermi
potential for discovery at IACTsin the Fermi/LHC era
S. Profumo: presented @TeVPA 2009, SLAC
59/81
The ATIC electron excess
60/81
The new (Nov09) Fermi e± spectrum
60
And in addition:tests that the resolutionIs enough
e± excess: May 09 result confirmed w/ improved precision & range; can be explained w/ standard physics (but doesn’t exclude DM). A crucial test on the cutoff will take > 1 year
CAN IACTs TAG POSITRONS?
61/81
Can Cherenkov distinguish positrons?
The task might be possible for multiple IACTsMoon shadow + geomagnetic field
Very hard, anyway worth trying…
TIBET AS-gamma
62/81
1-year data on halo: EGRET gamma excess ruled out
63/81
Going far away…
64/81
Variability: Mkn 421, Mkn501
Two very well studied sources, highly variable
Monitoring from Whipple, Magic…TeV-X Correlation
No orphan flares…See neutrino detectors
Mkn421 TeV-X-ray-correlation
Mkn421
However, recently Fermi/HESSsaw no correlation in PKS 2155
65/81
The highest energy flares
Three times in the last 2 years AGN transients have been observed more luminous than Vela/Crab
Scale: day or less
Can be explained by accretion mechanisms
MW scenario not yet completely clear, though
66/81
Rapid variability
HESS PKS 2155z = 0.116
July 2006Peak flux ~15 x Crab
~50 x averageDoubling times 1-3 min
RBH/c ~ 1...2.104 s
HESS PKS 2155z = 0.116
July 2006Peak flux ~15 x Crab
~50 x averageDoubling times 1-3 min
RBH/c ~ 1...2.104 s
H.E.S.S.arXiV:0706.0797
MAGIC, Mkn 501Doubling time ~ 2 min
MAGIC08
HESS08
67/81
Violation of the Lorentz Invariance?Light dispersion expected in some QG models, but interesting “per-se”
0.15-0.25 TeV
0.25-0.6 TeV
0.6-1.2 TeV
1.2-10 TeV 4 min lag
MAGIC Mkn 501, PLB08Es1 ~ 0.03 MP
Es1 > 0.02 MP
HESS PKS 2155, PRL08Es1 > 0.06 MP
anyway in most scenariosΔt ~ (E/Esα)
α, α>1VHE gamma rays are the probeMrk 501: Es2 > 3.10-9 MP , α=2
1st order
V = c [1 +- ξ (E/Es1) – ξ2 (E/Es2)2 +- …]
> 1 GeV
< 5 MeV
Es1
68/81
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= 0.034 is Δt = (0.030 ± 0.012) s/GeV; for HESS at
z~0.116, according to Ellis et al., Feb 09, Δt = (0.030 ± 0.027) s/GeV
Δt ~ (0.43 ± 0.19) K(z) s/GeV
Extrapolating, you get from Fermi (26 ± 11) s (J. Ellis et al., Feb 2009)
SURPRISINGLY CONSISTENT:
DIFFERENT SOURCE TYPE
DIFFERENT ENERGY RANGE
DIFFERENT DISTANCE
Es1
~z
69/81
z = 1.8 ± 0.4
one of the brightest GRBs
observed by LAT
after prompt phase, power-law emission persists in the LAT data as late as 1 kspost trigger:
highest E photon so far detected: 33.4 GeV, 82 s after GBM trigger
[expected from Ellis & al. (26 ± 13) s]
much weaker constraints on LIV Es
(EBL constraints)
Fermi: GRB 090510 GRB 090902
• z = 0.903 ± 0.003
• prompt spectrum detected,
significant deviation from Band
function at high E
• High energy photon detected:
31 GeV at To + 0.83 s
[expected from Ellis & al. (12 ± 5) s]
• tight constraint on Lorentz
Invariance Violation:
– MQG > x MPlanck [x = O(1)]
Nature 2009Nature 2009
70/81
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
More observations of flares will clarify the situation
71/81
GRBs
Long GRBs (lasting > 2 s) are associated with the explosive deaths of massive stars. The core collapses, and it forms a BH or a n star. The gamma rays are produced by shock waves created from material colliding within the jet.Short GRBs may originate from a variety of processes
merger of two n stars, or the merger of a BH and a n starcollapse of the core of a massive star into a black hole
Many crucial questions remain unansweredWhat types of stars die as GRBs? What is the composition of the jets? How are the gamma rays in the initial burst produced? What is the total energy budget of a GRB? How wide are the jet opening angles?
0.2 s
50 s
72/81
GRBs at VHE
MAGIC is the best instrument, due to
its fast movement & low threshold
MAGIC is in the GCN Network
GRB alert active since Apr 2005
No VHE No VHE γγ emission from emission from GRB positively detectedGRB positively detectedyet...yet...(all observed GRB very (all observed GRB very short or at very high z)short or at very high z)
Importance of decreasing the energy threshold to look further away
Blanch & Martinez 2005
region of opacity:
τ> 1
73/81
Propagation of γ-rays
x
xx
For γ−rays, relevant background component is optical/infrared (EBL)different models for EBL: minimum density given by cosmology/star
formation
Measurement of spectral features permits to constrain EBL models
≈
γVHEγbck → e+e-dominant process for absorption:
maximal for:
Heitler 1960
σ(β) ~
Mean free path
e+
e-
74/81
Selection bias?New physics?
adapted from De Angelis, Mansutti, Persic, Roncadelli MNRAS 2009
Are our AGN observationsconsistent with theory?
Selection bias?New physics ?
obse
rved
spe
ctra
l ind
exredshift
The most distant: MAGIC 3C 279 (z=0.54)
Measured spectra affected by attenuation in the EBL:
~ E-2
75/81
Interaction with a new light neutral boson? (De Angelis, Roncadelli & MAnsutti [DARMA], arXiv:0707.4312, PR D76 (2007) 121301arXiv:0707.2695, PL B659 (2008) 847
Explanations go from the standard ones
very hard emission mechanisms with intrinsic slope < 1.5 (Stecker2008)Very low EBL
to possible evidence for new physics
Oscillation to a light “axion”? (DA, Roncadelli & MAnsutti [DARMA], PLB2008, PRD2008)
Axion emission (Hooper et al., PRD2008)
Could it be seen?
76/81
A no-loss situation: if propagation is standard, cosmology with AGN
GRH depends on the γ–ray path and there the Hubble constant and the cosmological densities enter => if EBL density is known, the GRH might be used as a distance estimator
GRH behaves differently than other observables used for cosmology measures
Blanch & Martinez 2004
Simulatedmeasurements
Mkn 421Mkn 501
1ES1959+650Mkn 180
1ES 2344+514
PKS2005-489
1ES1218+3041ES1101-232
H2356-309PKS 2155-304H1426+428
EBL constraints can pave the way for the use of AGNs to fit ΩM and ΩΛ …
f(ΩΛ,ΩM,z’)
77/81
Determination of H0, ΩM and ΩΛ
Using the foreseen precision on the GRH measurements of 20 AGNs above z=0.1, the COSMOLOGICAL PARAMETERS can be fitted.
25.065.021.035.0
/Mpckm/s)6.15.68(0
±=Ω±=Ω±=
Λ
M
H
78/81
What next?
No hope to build a 10x better satellite soon, while it is ~easy to build a 10x better Cherenkov: a huge Cherenkov Telescope Array (CTA)
Fermi has been a great success (and now years to analyze & improve…)
Cherenkov telescopes have opened the new VHE window
79/81
Not to scale !
mCrab sensitivity in the 100 GeV–10 TeVdomain
O(12-14m) telescopes
A first (minimal) design: Core Array
CTA
energy thresholdof some 10 GeV(a) bigger dishes(b) dense-pack and/or(c) high-QE sensors
Low-energy section
Very very high-energy section: 10 km2 area at multi-TeV energies
80/81
A summary (oversimplified…)
10-14
10-13
10-12
10-11
10 100 1000 104 105
E [GeV]
Crab
10% Crab
1% Crab
Fermi
Magic
Magic2
Sen
sitiv
ity [
TeV
/cm
2 s ]
Agile
C T A
Argo
Hawc
Hess/Veritas
Far universeCutoff of pulsars
Fundamental physicsCosmic raysAt the knee
More sources
81/81
Summary
The recent years have opened a new (V)HE window on the Universe
VHE photons (often traveling through large distances) are a powerful probe of fundamental physics under extreme conditions
What better than a crash test to break a theory?
Observation of γ rays gives an exciting view of the VHE universeFermi resultsIACTs (~90/95 VHE sources discovered in the last 7 years, and growing…)
Transparency of the Universe: new physics?Rapid variability: new physics?
Just started, a lot of physics… and in 2010/2011:Analysis of 1st Fermi Catalog, new Fermi data (x2-3 improvement)factor 2-3 improvement by HESS2, MAGIC2, VERITASFor the future, large Cherenkov (CTA) would allow a leap…