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…