Vasileiadis GeorgeLUMP/Un. Montpellier II

for the H.E.S.S. Collaboration

Recent results of the High EnergyStereoscopic System (H.E.S.S.)

Outline

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Instruments for gamma-ray astronomyH.E.S.S. instrument and physicsprogramSelected recent discoveries

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Galactic sourcesNovel sources

➢ Fundamental physics:➢

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Search for dark matterTests of Lorentz invariance

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non-thermal emissionreveal cosmic acceleratorstwo main emission mechanisms:

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p0 decay (“hadronic”)inverse Compton scattering of

electrons (“leptonic”)

Gamma-ray astronomy

Goal: study the universe in the GeV-TeV energy range

Instruments forgamma-ray astronomy

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Comparison of the detection methods in gamma-ray astronomy

e.g. EGRET, Fermi

direct detection in spacee.g. Fermi-LAT:Si tracker withconversion foils +EM calorimeter

e.g. H.E.S.S., MAGIC, VERITAS

detect Cherenkov lightfrom gamma-ray inducedair showers

e.g. Milagro, HAWC,Tibet ASg, ARGO-YBJ

detect charged particlesin tails of gamma-rayinduced air showers

satellite-basedCherenkov telescopes high-altitude arrays

ground-based

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Cherenkov telescopes

e.g. H.E.S.S., MAGIC, VERITAS

detect Cherenkov lightfrom gamma-ray inducedair showers

high-altitude arrays

e.g. Milagro, HAWC,Tibet ASg, ARGO-YBJ

detect charged particlesin tails of gamma-rayinduced air showers

Comparison of the detection methods in gamma-ray astronomyground-based

300 GeV gamma-ray

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Comparison of the detection methods in gamma-ray astronomy

low energy threshold high sensitivity large aperture, high dutycycle

high-resolution spectradetailed morphological analysissurvey capability for limited skyregion

unbiased sky survey,transients < 100 GeVextended sources

unbiased sky surveyextended sourcestransients

satellite-basedCherenkov telescopes high-altitude arrays

ground-based

Energy rangeAreaEnergy resolutionAngular resolutionBackground suppressionApertureDuty cycle

0.1 - 300 GeV1m2

10% @ 1 GeV0.7° @ 1GeV> 99.99%2.4 sr> 90%

0.05 – 50 TeV100 000 m2

15%0.05°99%0.006 sr~10%

0.1 – 100 TeV30 000 m2

~50%0.3°-0.7°> 95%> 2 sr> 90%

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Gamma-ray astronomy with IACTs

IACT = Imaging atmospheric Cherenkov

telescope

Konrad Bernlöhr

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H.E.S.S.

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array of four imagingatmospheric Cherenkovtelescopeslocated in the Khomashighlands of Namibia, at1800m ASL

Eth = ~100 GeVDE/E = 15%angular resolution ~0.1°5° FoV

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Binaries

SNRsPWNePlerions

Survey

H.E.S.S. physics programExtended extragalactic objects

SNRPP

AGN

radio galaxiesGRBs

Astroparticle / Exotic

starburst galaxiesgalaxy clusterspair halos

Galactic Plane Survey andfollow-up observationsGalactic Center

MultiwavelengthCosmic raysDark matterLorentz invariance tests

Galactic sources

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Galactic Plane Survey

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large FoV enables systematic scanof Inner Galaxy, ongoing since2004aim: discovery of new gamma-raysources

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2300 h of good-quality datadataset = pointed observations +scan mode + hotspot follow-up

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over 60 Galactic VHE gamma-raysourcespopulation dominated by SNRs,PWNe, unidentified sourcesfocus in 2011:

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sensitivity goal of 2% Crabfor core region

deepening exposure in outerGalaxy

point-source sensitivity (G=2.5) for 5s detection, at latitude b = -0.3°H. Gast et al., proc.32nd ICRC (2011)

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First non-thermal shell SNRdiscovered based on gamma-ray observations!TeV and MWL data can beexplained in either hadronic orleptonic scenario.

RCW 86Vela Jr

Shell-type supernova remnants: HESS J1731-347H.E.S.S. collaboration,A&A in press

HESS J1731-347 HESS J1729-345

SN 1006•

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RX J1713.7-3946•

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possible interaction of SNR with a molecular cloud

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G318.2+0.1:VHE gamma-ray emissionfound in Galactic planesurveyCO data: molecular cloud

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(~106 Msun) found at either3.5 or 9.2kpcAssuming near solution andn~1/cm3: age ~8000 years:Sedov phase

➢ Possible scenario:emission from cosmic raysaccelerated in the SNR andilluminating the MC

843 MHz radio imageG318.2+0.1

CO radio data (Dame et al., 2001)

G318.2+0.1 inVHE gamma-rays

P. Hofverberg et al.,arXiv: 1104.5119

Novel sources

ESO

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Starburst galaxies

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Strongly enhancedstar-formation rate i.e.high supernova rateConsequence: highcosmic ray (CR)density

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High gas densityIntense radiation fieldsPromising conditionsfor gamma-rayproduction

stellar nurseries

interesting test ofstandard paradigm forcosmic-ray production

Starburst galaxy NGC 253 (optical)

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Starburst galaxy NGC253

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119 hours of good observationsadvanced image analysis techniquesintegral flux roughly 0.3% Crab: oneof the faintest sources detected so farin VHE gamma raysPoint-like emission, consistent withstarburst nucleus

x-rayVHE gamma-rayoptical

H.E.S.S. collaboration, Science 326 (2009) 1080-1082

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Starburst galaxy NGC253

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Hadronic scenario: TeV cosmic-ray density in the starburst regionabout three orders of magnitudelarger than at the location of theEarthAbout 5% of the energy in CRsconverted into gamma raysVeritas detection of M82, Fermidetection of NGC253 and M82

F. Acero et al.,Science 326 (2009) 1080

starburst galaxies emerging as new source class in gamma-ray astronomy

ESO

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Terzan 5

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near-IR image of Terzan 5

40 arcsec

Globular cluster Terzan 5:largest population of identifiedmillisecond pulsars and high stellardensity at its coreelectrons accelerated by millisecondpulsars themselves or in their collidingwindsintense stellar radiation fieldintegral VHE gamma-ray flux matchesPredictionsFew possibilities as of the origin of thisVHE source under discussion. ! First time observed

H.E.S.S. collaboration,A&A 531 (2011) L18

Fundamental physics

The Dark Matter of the Universe

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+, , g.

[AMS, Neutrino Telescopes, GLAST, Cherenkov Telescopes]

In Standard Cosmology Cold Dark Matter is favoured

Weakly Interacting Massive Particles (WIMPs)

WIMPs must be beyond the Standard Model

BUT... No confirmed detection yet.

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 ?

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Search for Dark Matter

➢ gamma-ray flux from dark matter annihilations:

DM density profiles of the Galactic halo annihilation spectra for different WIMP models

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➢ Galactic Center Halo- |b| > 0.3° to excludeastrophysical backgrounds- rsource> rbg-region

➢ dwarf galaxiessystems dominated by darkmatter

Recent results of indirect dark matter searchcompilation of limits for neutralino LSP

Best H.E.S.S. limits currently in the range3x10-25 to 3x10-24 cm3s-1.

H.E.S.S. Collaboration,PRL 106 (2011) 161301Astropart. Phys. 34 (2011) 608ApJ 735 (2011) 12

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

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• 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)

• Use pulse-shape of giant AGN flare, to search for energy-dependent velocity of gamma-ray photons. Ideal candidate: PKS 2155 flare of July 28th, 2006.

• Lightcurve for low energy range (0.25-0.28 TeV) as temporal template.• No hint for Lorentz invariance violation found. 95% CL upper limits:

MlQG>2.1 1018 GeV Mq

QG> 6.4 1010 GeV

Test of Lorentz invariance

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H.E.S.S. II

➢ lower threshold to ~50 GeV:➢

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pulsar physicsAGN physicsdark matter searchoverlap with Fermi-LAT energy range

➢ on track for first light in June 2012

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H.E.S.S. II

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Summary

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H.E.S.S. Galactic Plane Survey continuesdiscovering new sources.Novel source classes can still bediscovered.Important contributions to fundamentalphysics.H.E.S.S.-I mirror refurbishments inprogress. H.E.S.S.-II nearing completion,first light foreseen in June 2012.

➢ TeV gamma-ray astronomy has turnedinto a mature field, with over 120sources known to date.