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Cosmology with VHE Gamma Ray Telescopes.

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Title: Cosmology with VHE Gamma Ray Telescopes.


1
Cosmology with VHE Gamma Ray Telescopes.
IRGAC 2006
  • Manel Martinez

Barcelona, 13-Jul-2006
2
Outline
  • Introduction
  • Instruments and techniques
  • Status and prospects for Measurements related to
    Cosmology
  • - Dark Matter Searches
  • - The Gamma Ray Horizon
  • - Invariance of speed of light

3
Introduction
  • Very special moment in VHE Cosmic gamma-ray
    observation
  • real revolution in consolidation of
    Cherenkov telescopes as astronomical instruments
  • gt transition from HE experiments to
    telescopic installations
  • --gt exploding interest in the
    astronomical community !
  • New generation of instruments producing a big
    observational step in the last few years
  • - quantitative (tripling number of detected
    sources)
  • - qualitative (extremely high quality gt
    unprecedented detailed studies in Spectra,
    Morphology, Time Variation).
  • gt DOWN OF A GOLDEN AGE FOR CHERENKOV
    TELESCOPES !

4
The VHE Sky - 1995
The VHE Sky - 1995
Mrk421
Mrk501
Crab
R.A.Ong Aug 2005
5
The VHE Sky - 2003
The VHE Sky - 2003
Mrk421
H1426
M87
Mrk501
1ES1959
RXJ 1713
Cas A
GC
Crab
TeV 2032
1ES 2344
PKS 2155
R.A.Ong Aug 2005
6
Second generation telescopes
MAGIC (2004)
HESS (2003)
VERITAS (2006)
CANGAROO-III (2004)
7
8-15 additional sources in galactic plane.
Nadia Tonello
8
HESS Galactic Plane Survey
Sources gt 6 sigma 9 new, 11
total Sources gt 4 sigma 7 new
  • Most sources
  • Shell-type SNR
  • Pulsar-Wind-Nebulae
  • Unidentified
  • New objects

330
9
H.E.S.S. Highlight Resolved
Supernova-Remnants
RX J1713-3946
10
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

11
High time-resolution study of AGN flare
Preliminary
  • Huge Mkn 501 flare on 1st July 2005 -gt 4 Crab
    intensity.
  • Intensity variation in 2 minute bins -gt new,
    much stronger, constraints on emission mechanism
    and light-speed dispersion relations (effective
    quantum gravity scale).

Crab
2 minutes time bins
12
Detection of TeV gamma rays using
Cherenkovtelescopes
Observation Technique
13
Image intensity ? Shower energy
Image orientation ? Shower direction
Image shape ? Primary particle
14
Getting rid of CR background I
Image parameterization
(1) Orientation g-rays point to the source
excess at small alpha
15
Getting rid of CR background II
z
g
y
16
Systems of Cherenkov telescopes
Better bkgd reduction Better angular
resolution Better energy resolution
Slide fro Pr W. Hofmann
17
The VHE g-ray Physics Program
SNRs
Origin of Cosmic Rays
Microquasars
AGNs
GRBs
Cold Dark Matter
cosmological g-Ray Horizon
Test of the speed of light invariance
18
A glimpse on the Physics Potential related to
Cosmology
  • COSMOLOGY one of the most exciting research
    subjects of present Astrophysics and High Energy
    Physics.
  • Concordance Cosmological Standard Model fitting
    all measurements -gt Becoming COSMONOMY
  • VHE gamma-ray telescopes may contribute in
    subjects such as
  • - Origin of Dark Matter
  • - Cosmological Gamma Ray Horizon
  • - Tests of speed of light Invariance
  • -

19
Indirect Searches for Cold Dark Matter with
IACTs
20
The Dark Matter of the Universe
In Standard Cosmology Cold Dark Matter is favoured
Weakly Interacting Massive Particles (WIMPs)
WIMPs must be beyond the Standard Model
Many experiments are trying/projected to find
WIMPs DIRECTLY collision with ordinary
matter in dedicated underground
experiments. DAMA, GENIUS, CDMS, CRESST,
... INDIRECTLY Annihilation processes
producing antiprotons, e, ?, ?. AMS, Neutrino
Telescopes, GLAST, Cherenkov Telescopes
BUT... No confirmed detection yet.
21
Gamma Flux predictions
  • For gammas coming from WIMP annihilation ,
    expected observable flux is

  • WIMP MODEL DARK MATTER
    DISTRIBUTION MODEL

  • gt calculation factorizes !
  • Large uncertainties in the predictions
  • - WIMP models -gt WIMP mass and cross
    section
  • - Dark Matter distribution models -gt very
    sensitive to how cuspy is the density profile

22
The most plausible Dark Particle
  • Supersymmetric extension of the Standard Model
    (SUSY) provides
  • the Neutralino ( )
  • as a suitable candidate for WIMP
  • Lightest supersymmetric particle
  • Stable. (if R-parity conserved)
  • Weakly interacting mixture of neutral s-fermions
  • Bino Wino Higgsino1
    Higgsino2
  • Gauginos
    Higgsino
  • Massive 100 GeV - 1 TeV

?
23
Neutralino Indirect searches
Mono-energetic g-lines Loop suppressed
annihilations.
24
Prospects for Indirect detection
25
Where to look for Cold Dark Matter in our
neibourghood ?
  • WIMPs would constitute the galactic halo and
    would concentrate at
  • - the galaxy center
  • - dark matter clumps
  • - visible satellites
  • - invisible satellites
  • - nearby galaxies (M31)

26
Best targets for Dark Matter searches
Galactic Center

g-ray flux from c annihilation
Density and mass profiles
Flix, Klypin, Martinez, Prada, Simonneau
27
Galactic Center
syst. error
-gt No significant variability from year to
minute scales (in 40 h obs. time
distributed over 2 years)
28
Dark matter annihilation ?
Preliminary
proposed based on early H.E.S.S. data
proposed before H.E.S.S. data
? J. Ripken ICRC 2005
29
Gamma ray spectrum
  • Unbroken power law, index 2.3

Preliminary
Preliminary
  • Very unlikely to be dark matter.
  • Presence of a strong gamma-ray source outshines
    any possible DM signal

30
The Galactic Center region
Proximity (8 kpc) and possibly high DM
concentration BUT Extreme environment Totally
obscured in the Optical Only visible from Radio
to IR and high energies GC contains 10 of
galactic interstellar medium giant molecular
clouds Host the nearest hypothetical
super-massive BH Variety of VHE emitters SNRs,
Molecular Clouds, non-thermal arcs...
31
The Galactic Centre Ridge
H.E.S.S.
Galactic Centre gamma-ray count map
Same map after subtraction of two dominant point
sources gt Clear correlation with molecular gas
traced by its CS emission
32
Best targets for Dark Matter searches
  • - Dwarf spheroidal galaxies with M/L 100-200

DRACO ?cul 30º RA15 08.2 - DEC 67 23 D
82 Kpc. CACTUS claim under scrutiny.
7 hours ? 30000 excess events above the
background. Angular region extending
approximately 1 degree around the center of
Draco. CACTUS telescope has a rather poor angular
resolution of 0.3º Crab nebula. Most of the
excess events are low energetic, between 50 GeV
and 150 GeV.
DRACO dwarf galaxy
33
Best targets for Dark Matter searches
  • - Dark Matter halo substructure
  • Compact High Velocity Clouds.
  • (as missing satellites)
  • as gamma diffuse background.

Simulation of local group 300 satellites with
Vcirc gt 10 km/s
Anatoly Klypin
34
Dark Matter searches conclusions
  • VHE g-ray astronomy might provide WIMP
    annihilation signals but actual detection
    potential somewhat uncertain because
  • - WIMP mass spectrum and couplings should be
    known to determine the annihilation probabilities
    into the different channels -gt important
    accelerator and relic density constraints but
    still too many possibilities open. Help from LHC
    ?
  • - The cuspy region of the dark matter density
    profiles virtually unknown.
  • - Background due to astrophysical sources.

35
Dark Matter searches conclusions
  • GLAST catalogue together with VHE telescopes may
    be instrumental for DM searches
  • - GLAST unid. sources might spot DM clumps
  • - Spectra features provided by VHE telescopes
    very important to pinpoint DM signatures
  • So far no confirmed detection and the enterprise
    to claim DM signals looks challenging but very
    important to continue because
  • gt even if WIMP candidates are found in
    accelerator experiments it must be confirmed that
    they actually are constituents of the Dark Matter
    of our universe.

36
Cosmological measurements from VHE Gamma Ray
absorption
37
Extragalactic TeV astronomy
  • Space is filled with diffuse extragalactic
    background light sum of starlight emitted by
    galaxies through history of universe
  • Gamma Rays absorbed by interaction with
    Background radiation fields

EBL
W.Hofmann
38
Optical Depth and GRH
High energy ?-rays traversing cosmological
distances are expected to be absorbed through
their interactions with the EBL by
Then the ?-ray flux is suppressed while
travelling from the emission point to the
detection point.
Where the Opacity ?(E,z) is
The e-fold reduction ( ?(E,z) 1) is the Gamma
Ray Horizon (GRH).
39
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40
Present IACT range
M.Schroedter astro/ph-0504397
41
CERN Courier June 2006
42
AGN Summary
Source Redshift Type First Detection Confimation
M87 0.004 FR I HEGRA HESS
Mkn 421 0.031 BL Lac Whipple Many
Mkn 501 0.034 BL Lac Whipple Many
1ES 2344514 0.044 BL Lac Whipple HEGRA
Mkn 180 0.045 BL Lac MAGIC
1ES 1959650 0.047 BL Lac Tel. Array Many
PKS 2005-489 0.071 BL Lac HESS
PKS 2155-304 0.116 BL Lac Mark VI HESS
H1426428 0.129 BL Lac Whipple Many
H2356-309 0.165 BL Lac HESS
1ES 1218304 0.182 BL Lac MAGIC
1ES 1101-232 0.186 BL Lac HESS
PG 1553113 lt0.78 BL Lac HESS-MAGIC MAGIC
? Reaching further out in redshift.
43
MAGIC
H.E.S.S.
44
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45
Spectra ExtragalacticBackgroundLight
  • EBL resolved
  • Universe more
  • transparent

X
measure- ments
upper limits
X
lower limits from galaxy counts
46
VHE gamma-ray absorption Conclusions
  • Hard spectrum of new AGNs observed at z1.6-1.8
    allows strong constraints on absorption due to
    EBL density in the visible-infrared region.
  • EBL density close to lower limits from galaxy
    counts using HST and Spitzer
  • gt EBL basically consistent with resolved
    sources.
  • EBL much smaller than anticipated the universe
    is more transparent to VHE gamma rays than
    expected gt farther reach in redshift gt many
    more AGNs could be seen.
  • If EBL resolved, GRH could be turned around as a
    (absorption) distance estimator (crazy and
    speculative ?).

47
How to do it ?
If spectrum measured in a broad band of energy
adjust simultaneously intrinsic spectrum and
absorption gt need low-threshold and large
sensitivity instruments (multiwavelength
measurements together with GLAST will help).
48
GRH measurement is constraining the EBL density
Blanch Martinez 2004
Different EBL models
Simulated measurements
Mkn 421 Mkn 501
1ES 2344514 Mkn 180 1ES1959650
PKS2005-489
PKS 2155-304 H1426428
1ES1218304 1ES1101-232
H2356-309
49
Cosmological Parameters
GRH depends on the ?ray path and there the
Hubble constant and the cosmological densities
enter gt if EBL density is known, the GRH might
be used as a distance estimator
GRH behaves differently than other observables
already used for cosmology measurements.
50
EBL constraint is paving the way for the use of
AGNs to fit WM and WL
Blanch Martinez 2004
PKS2005-489
PKS 2155-304 H1426428
H2356-309
1ES1959650 Mkn 180 1ES 2344514
1ES1218304 1ES1101-232
Mkn 421 Mkn 501
Simulated measurements
51
Determination of H0, ?M and ??
Using the foreseen precision on the GRH
measurements of 20 extrapolated EGRET AGNs, the
COSMOLOGICAL PARAMETERS can be fitted.
We take the scenario where Ho is known from
other experiments at the level of 4 km/ s Mpc
(Hubble project).
MINOS
gt The Dc22.3 2-parameter contour improves by
more than a factor 2 the 2004 Supernovae
combined result !
52
Measurement of Cosmological Parameters
Conclusions
  • Low-threshold and high sensitivity IACT arrays
    might be able to measure the GRH for a large
    sample of sources in a moderate redshift range at
    a few level.
  • The GRH dependence on the COSMOLOGICAL PARAMETERS
    gives a method to calculate them that
  • - is independent on the current ones
  • - does not rely on the existence of standard
    universal candles
  • - is complementary to the existing Supernovae
    Ia because it explores a different universe
    expansion epoch uses AGN as sources
  • This method might be able to put relevant
    constraints on the cosmological densities.

53
Searching for energy dependence of the speed of
light with IACTs
54
Tests of Lorenz Invariance Breaking effects.
  • Quantum Gravity theories predict Lorentz
    Invariance breaking at very large energies.

EQG O(MP ) 1.22 x 1019 GeV gt
LQG O(LP) 1.6 x 10-35 m.
  • Large extra dimension theories predict a similar
    effect at much smaller energy scales O(1 TeV).
  • Consequence small LI violating terms modify
    free-field propagators
  • Different maximal attainable velocity for
    different particles

ce cg(1d), 0 lt abs(d) ltlt 1 Stecker
and Glashow
55
  1. If dlt0 gt ce lt cg gt decay g -gt ee-
    kinematically allowed for gamma with energies
    above

Emax me sqrt(2/abs(d))
- Eg gt 50 TeV from Crab Nebula gt abs(d) lt 2 x
10-16

2. If dgt0 gt ce gt cg gt electrons become
superluminal for energies larger than
Emax/Sqrt(2) gt Vacuum Cherenkov Radiation.
  • - Ee gt 2 TeV from cosmic radiation gt abs(d) lt 2
    x 10-14
  • Modification of g g -gt ee- threshold. Using Mkn
    501 and Mkn 421 spectra observations up to Eg gt
    20 TeV
  • gt abs(d) lt 1.3 x 10-15

56
Energy dependence of the Speed of light
  • Space-time at large distances is smooth but,
    if Gravity is a quantum theory, at very short
    distances it might show a very complex ( foamy
    ) structure due to Quantum fluctuations.
  • A consequence of these fluctuations is the fact
    that the speed of light in vacuum becomes energy
    dependent.
  • The energy scale at which gravity is expected to
    behave as a quantum theory is the Planck Mass
  • EQG O(MP ) O(1019) GeV

57
  • From a purely 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 DE and the path L to the source
  • 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.

58
  • In addition one needs very fast transient
    phenomena providing a time stamp for the
    simultaneous emission of different energy g
    rays.
  • Good source candidates are
  • - Very distant Blazars showing fast flares
  • - Gamma-Ray-Bursts (GBR)

59
The Whipple QG limit
  • Limits to Quantum Gravity Effects from
    Observations of TeV Flares in Active Galaxies
    Phys.Rev.Lett.83 (1999) 2108
  • Huge Mkn 421 flare -gt
  • 280 second time intervals and 2 energy bins
  • EQE gt MP/250 _at_ 95 CL

60
  • The same local deformation of space-time which
    originates a dispersion relation for the speed of
    light, has as a consequence a local
    non-conservation of energy-momentum
    (Lorenz-invariance deformation) which changes the
    energy threshold for the absorption of gamma rays
    in the process
  • g HE g IR -gt e e- gt shortening of the
    g-ray horizon

EQGMP/100
EQGMP
61
Tests of energy dependence of the speed of light
conclusions
  • IACTs might provide the opportunity of testing
    directly the quantum nature of Gravity up to
    effective scales of the order of the Planck mass.
  • That requires the study of a sample of very fast
    flaring objects at different redshifts, namely
    Blazars and GBRs, which is expected to be
    observed by IACTs thanks to their high flux
    sensitivity.

62
Outlook What next ?
  • Cherenkov Telescopes
  • VERITAS
  • 4x 12m telescopes at Kitt-Peak in 2006.

MAGIC-II
MAGIC-I
  • MAGIC-II
  • Improved 17m telescope.
  • Faster FADCs and a high-QE camera.
  • First light in 2007.

85m
  • HESS-II
  • New 28m telescope.
  • 2048 pixel camera.
  • Lower energy 40-50 GeV
  • First light in 2008.

63
Outlook What next ?
64
Outlook What next ?
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