Title: Cosmology with VHE Gamma Ray Telescopes.
1Cosmology with VHE Gamma Ray Telescopes.
IRGAC 2006
Barcelona, 13-Jul-2006
2Outline
- Introduction
- Instruments and techniques
- Status and prospects for Measurements related to
Cosmology - - Dark Matter Searches
- - The Gamma Ray Horizon
- - Invariance of speed of light
3Introduction
- 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 !
4The VHE Sky - 1995
The VHE Sky - 1995
Mrk421
Mrk501
Crab
R.A.Ong Aug 2005
5The 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
6Second generation telescopes
MAGIC (2004)
HESS (2003)
VERITAS (2006)
CANGAROO-III (2004)
7 8-15 additional sources in galactic plane.
Nadia Tonello
8HESS 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
10Spectra
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
12Detection of TeV gamma rays using
Cherenkovtelescopes
Observation Technique
13Image intensity ? Shower energy
Image orientation ? Shower direction
Image shape ? Primary particle
14Getting rid of CR background I
Image parameterization
(1) Orientation g-rays point to the source
excess at small alpha
15Getting rid of CR background II
z
g
y
16Systems 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
18A 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
- -
-
19Indirect Searches for Cold Dark Matter with
IACTs
20The 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.
21Gamma 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
22The 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
?
23Neutralino Indirect searches
Mono-energetic g-lines Loop suppressed
annihilations.
24Prospects for Indirect detection
25Where 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)
26Best targets for Dark Matter searches
Galactic Center
g-ray flux from c annihilation
Density and mass profiles
Flix, Klypin, Martinez, Prada, Simonneau
27Galactic Center
syst. error
-gt No significant variability from year to
minute scales (in 40 h obs. time
distributed over 2 years)
28Dark matter annihilation ?
Preliminary
proposed based on early H.E.S.S. data
proposed before H.E.S.S. data
? J. Ripken ICRC 2005
29Gamma 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
30The 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...
31The 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
32Best 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
33Best 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
34Dark 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.
35Dark 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.
36Cosmological measurements from VHE Gamma Ray
absorption
37Extragalactic 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
38Optical 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(No Transcript)
40Present IACT range
M.Schroedter astro/ph-0504397
41CERN Courier June 2006
42AGN 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.
43MAGIC
H.E.S.S.
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45Spectra ExtragalacticBackgroundLight
- EBL resolved
- Universe more
- transparent
X
measure- ments
upper limits
X
lower limits from galaxy counts
46VHE 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 ?). -
47How 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).
48GRH 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
49Cosmological 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.
50EBL 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
51Determination 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 !
52Measurement 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.
53Searching for energy dependence of the speed of
light with IACTs
54Tests 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- 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
56Energy 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)
59The 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
61Tests 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.
62Outlook What next ?
- 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.
63Outlook What next ?
64Outlook What next ?