Cosmology with VHE Gamma Ray Telescopes.

Manel Martinez

Barcelona, 13-Jul-2006

IRGAC 2006

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

Introduction

• Very special moment in VHE Cosmic gamma-ray observation:

real revolution in consolidation of Cherenkov telescopes as astronomical instruments

=> transition from “HE experiments” to “telescopic installations”

--> 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 => unprecedented detailed studies in Spectra, Morphology, Time Variation).

=> => DOWN OF A DOWN OF A GOLDEN AGEGOLDEN AGE FOR CHERENKOV TELESCOPES ! FOR CHERENKOV TELESCOPES !

The VHE Sky - 1995

Mrk421

Mrk501

Crab

R.A.OngAug 2005

Pulsar Nebula

SNR

AGN

Other, UNID

The VHE Sky - 1995

The VHE Sky - 2003

Mrk421 H1426

Mrk501

1ES1959

1ES 2344

PKS 2155

Cas A

RXJ 1713

CrabTeV 2032

M87

GC

R.A.OngAug 2005

Pulsar Nebula

SNR

AGN

Other, UNID

The VHE Sky - 2003

Second generation telescopes

MAGIC (2004)

VERITAS (2006)

CANGAROO-III (2004)

HESS (2003)

+ 8-15 additional sourcesin galactic plane.

Nadia Tonello

330°

HESS Galactic Plane Survey

Sources > 6 sigma: 9 new, 11 total

Sources > 4 sigma: 7 new

Most sources:

• Shell-type SNR

• Pulsar-Wind-Nebulae

• Unidentified

• New objects

H.E.S.S. Highlight:H.E.S.S. Highlight: Resolved Supernova-Remnants Resolved Supernova-Remnants

RX J1713-3946

SpectraSpectra

Preliminary

Index ~ 2.1 – 2.2Little variation across SNRCutoff or break at high energy

Acceleration ofprimary particlesin SNR shock towell beyond 100 TeV

High time-resolution study of AGN flare

• Huge Mkn 501 flare on 1st July 2005 -> 4 Crab intensity.

• Intensity variation in 2 minute bins -> new, much stronger, constraints on emission mechanism and light-speed dispersion relations (effective quantum gravity scale).

Preliminary

2 minutes time bins

Crab

Gamma-ray

~ 10 kmParticleshower

Detection of TeV gamma

rays

using Cherenkovtelescopes

~ 1o

Che

renk

ov li

ght

~ 120 m

Observation Technique

Image intensity Shower energy

Image orientation Shower direction

Image shape Primary particle

Better bkgd reduction Better angular resolutionBetter energy resolution

Systems of Cherenkov telescopes

Slide fro Pr W. Hofmann

SNRsSNRs

Cold Cold Dark Dark

MatterMatter

PulsarsPulsars

GRBsGRBs

Test of the Test of the speed of light speed of light

invarianceinvariance

cosmologiccosmologicalal-Ray -Ray HorizonHorizon

AGNsAGNs

The VHE -ray Physics Program

Origin of Origin of Cosmic Cosmic RaysRays

MicroquasarsMicroquasars

Indirect Searches for

Cold Dark Matter with IACTs

• For gammas coming from WIMP annihilation , expected observable flux is:

WIMP MODEL DARK MATTER DISTRIBUTION MODEL

=> calculation factorizes !

• Large uncertainties in the predictions: - WIMP models -> WIMP mass and cross section - Dark Matter distribution models -> very

sensitive to how cuspy is the density profile

l.o.s

2

2)()(

4)(

dll

M

Ndm

WIMP

Gamma Flux predictions

Neutralino – Indirect searches

lines

continuum

,

d

e

p

Point back to source Search for excess components

in cosmic rays (DIFUSION)

Z

Mono-energetic -linesLoop suppressed annihilations.

Continuum -ray spectraFrom 0s decays.Spectra extends up to m.

Prospects for Indirect detection

WIMPs would constitute the galactic halo and would concentrate at

- the galaxy center

- dark matter clumps

- visible satellites

- invisible satellites

- nearby galaxies (M31)

Where to look for Cold Dark Matter in our neibourghood ?

Galactic CenterGalactic Center

SGR A

Point-like core

Extended tailSimilar to NFW profile

-> Consistent with SGR A* to 6’’ and slightly extended.

-> No significant variability from year to minute scales (in ~40 h obs. time distributed over 2 years)

syst. error

10-13

10-12

10-11

0,1 1 10

E2 F

(E)

[Te

V/c

m2 s]

E [TeV]

Dark matter annihilation ?Dark matter annihilation ?

20 TeV Neutralino

20 TeV KK particle proposed beforeH.E.S.S. data

proposed based on early H.E.S.S. data

J. Ripken ICRC 2005

Preliminary

Gamma ray spectrumGamma ray spectrum

PreliminaryUnbroken power law, index 2.3

Preliminary

Good agreement between HESS andMAGIC (large zenith angle observation).

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

The Galactic Center region

Proximity (~8 kpc) and possibly high DM concentration

BUT

Extreme environment

Totally obscured in the OpticalOnly visible from Radio to IR and high energies

GC contains:

10 % of galactic interstellar medium [giant molecular clouds]

Host the nearest [hypothetical] super-massive BHVariety of VHE emitters: SNRs, Molecular Clouds, non-

thermal arcs...

The Galactic Centre Ridge

Same map after subtraction of two dominant point sources =>Clear correlation with molecular gas traced by its CS emission

Galactic Centre gamma-ray count map

H.E.S.S.

Best targets for Dark Matter searches

- - Dwarf spheroidal galaxies with M/L ~ 100-200:Dwarf spheroidal galaxies with M/L ~ 100-200:

· DRACODRACO: cul ~ 30º

RA15 08.2 - DEC +67 23

D = 82 Kpc. CACTUS claim under scrutiny.

DRACO dwarf galaxyDRACO dwarf galaxy

7 hours 30‘000 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.

Dark Matter searches: conclusions

•VHE VHE -ray -ray astronomy might provideastronomy might provide WIMP WIMP annihilation signalsannihilation signals but but actual detection potential detection potential somewhat uncertainsomewhat uncertain because because : :

- WIMP- WIMP mass spectrum and couplings should be known to mass spectrum and couplings should be known to determine the annihilation probabilities into the different determine the annihilation probabilities into the different channelschannels -> important accelerator and relic density constraints -> important accelerator and relic density constraints but still too manybut still too many possibilities possibilities open. Help from LHC ? open. Help from LHC ?

- The cuspy region of the dark matter density profiles virtually - The cuspy region of the dark matter density profiles virtually unknown.unknown.

- Background due to astrophysical sources.- Background due to astrophysical sources.

Dark Matter searches: conclusions

• GLAST catalogue together with VHE telescopes may be GLAST catalogue together with VHE telescopes may be instrumental for DM searches:instrumental for DM searches: - GLAST unid. sources might spot DM clumps- GLAST unid. sources might spot DM clumps - Spectra features provided by VHE telescopes very - Spectra features provided by VHE telescopes very important to pinpoint DM signaturesimportant to pinpoint DM signatures

•So far no confirmed detection and the enterprise to So far no confirmed detection and the enterprise to claimclaim DM signals looks DM signals looks challenging challenging but very important to but very important to continue becausecontinue because:: => even if WIMP candidates are => even if WIMP candidates are foundfound in accelerator in accelerator experiments it must be confirmed that they actually experiments it must be confirmed that they actually are are constituents of theconstituents of the Dark Matter of our universe.Dark Matter of our universe.

Cosmological measurements from

VHE Gamma Ray absorption

Extragalactic TeV astronomyExtragalactic TeV astronomy

Space is filled with diffuse extragalactic background light: sum of starlight emitted by galaxies through history of universeGamma Rays absorbed by interaction with Background radiation fields

EBLx

xx

VHEEBL e+e-

W.Hofmann

Optical Depth and GRH

eeEBLHEThen the -ray flux is suppressed while travelling from the emission point to the detection point.

The e-fold reduction ( (E,z) = 1) is the Gamma Ray Horizon (GRH).

z,Ee 0

High energy -rays traversing cosmological distances are expected to be absorbed through their interactions with the EBL by:

2

22

1

2

22

00

12,2

,

zEx

cm

z

q zxEzndx

dxzd

dlzdzE

q

Where the Opacity E,zis:

M.Schroedter astro/ph-0504397

Present IACT range

AGN SummaryAGN 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 2344+514 0.044 BL Lac Whipple HEGRA

Mkn 180 0.045 BL Lac MAGIC

1ES 1959+650 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

H1426+428 0.129 BL Lac Whipple Many

H2356-309 0.165 BL Lac HESS

1ES 1218+304 0.182 BL Lac MAGIC

1ES 1101-232 0.186 BL Lac HESS

PG 1553+113 <0.78 BL Lac HESS-MAGIC MAGIC

Reaching further out in redshift.

1 ES 1101 = 2.9±0.2

H 2356 (x 0.1) = 3.1±0.2

EBL

Source spectrum = 1.5

Preliminary

H.E.S.S.

MAGIC

Spectra & ExtragalacticBackgroundLight

lower limitsfrom galaxy

counts

measure-ments upper

limits

Reference shape

HESS limits

X

XEBL resolvedUniverse more

transparent

VHE gamma-ray absorption: Conclusions

• Hard spectrum of new AGNs observed at z~1.6-1.8 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

=> EBL basically consistent with resolved sources.

• EBL much smaller than anticipated: the universe is more transparent to VHE gamma rays than expected => farther reach in redshift => many more AGNs could be seen.

• If EBL resolved, GRH could be turned around as a (absorption) distance estimator (crazy and speculative ?).

How to do it ?

If spectrum measured in a broad band of energy: adjust simultaneously intrinsic spectrum and absorption => need low-threshold and large sensitivity instruments (multiwavelength measurements together with GLAST will help).

GRH measurement is constraining the EBL density

Blanch & Martinez 2004

Simulatedmeasurements

Different EBL models

Mkn 421Mkn 501

1ES 2344+514Mkn 180

1ES1959+650

PKS 2155-304H1426+428

PKS2005-489

1ES1218+3041ES1101-232H2356-309

Cosmological Parameters

GRH depends on the –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

2123

0 11

11/

kM zzH

z/c

dzdl

GRH behaves differently than other observables already used for cosmology measurements.

EBL constraint is paving the way for the use of AGNs to fit M and …

Blanch & Martinez 2004

Simulatedmeasurements

Mkn 421Mkn 501

1ES1959+650Mkn 180

1ES 2344+514

PKS2005-489

1ES1218+3041ES1101-232

H2356-309PKS 2155-304H1426+428

Determination of H0, M and

Using the foreseen precision on the GRH measurements of 20 extrapolated EGRET AGNs, the COSMOLOGICAL PARAMETERS can be fitted.

=> The 2=2.3 2-parameter contour improves by more than a factor 2 the 2004’ Supernovae combined result !

25.024.065.0

20.021.035.0

/6.16.15.680

M

MpcskmH

MINOS

We take the scenario where Ho is known from other experiments at the level of 4 km/ s Mpc (Hubble project).

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.

Searching for energy dependence of the speed

of light with IACTs

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

EEQGQG = O(M = O(MPP )= O(10 )= O(101919) GeV) GeV

• From a purely phenomenological point of view, the effect can be studied with a perturbative expansion. In first order, the arrival delay of rays emitted simultaneously from a distant source should be proportional to their energy difference E 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 -rays coming from sources at cosmological distances.

c

L

E

Et

QG

• In addition one needs very fast transient phenomena providing a “time stamp” for the “simultaneous” emission of different energy –rays.

• Good source candidates are: - Very distant Blazars showing fast flares - Gamma-Ray-Bursts (GBR)

• “Limits to Quantum Gravity Effects from Observations of TeV Flares in Active Galaxies” Phys.Rev.Lett.83 (1999) 2108

• Huge Mkn 421 flare -> 280 second time intervals

and 2 energy bins

EQE > MP/250 @ 95% CL

The Whipple QG limit

• 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.

Tests of energy dependence of the speed of light:

conclusions

Cherenkov TelescopesCherenkov Telescopes

HESS-II

• New 28m telescope.

• 2048 pixel camera.

• Lower energy 40-50 GeV

• First light in 2008.

MAGIC-II

• Improved 17m telescope.

• Faster FADCs and a high-QE camera.

• First light in 2007.

MAGIC-IMAGIC-I MAGIC-IIMAGIC-II

85m

Outlook: What next ?

VERITAS

• 4x 12m telescopes at Kitt-Peak in 2006.

Outlook: What next ?

Outlook: What next ?