1. Cosmology and VHE Gamma Ray astrophysics: connections and perspectives. Manel Martinez Barcelona, 7-Jul-2006 THE MULTI-MESSENGER APPROACH TO UNIDENTIFIED GAMMA-RAY SOURCES (Third Workshop on the Nature of Unidentified High-Energy Sources)

2. SNRs Cold Dark Matter Pulsars GRBs Test of the speed of light invariance cosmological  -Ray Horizon AGNs The VHE  -ray Physics Program Origin of Cosmic Rays Microquasars

3. 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 -> 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 - …

4. Indirect Searches for Cold Dark Matter with IACTs

5. The Dark Matter of the Universe experiments 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] Cold Dark Matter 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.

6. 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 Gamma Flux predictions

7. 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 

8. Neutralino – Indirect searches Point back to source Search for excess components in cosmic rays (DIFUSION)   Z Mono-energetic  -lines Loop suppressed annihilations. Continuum  -ray spectra From  0 s decays. Spectra extends up to m .

9. Prospects for Indirect detection

10. 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 ?

11. Best targets for Dark Matter searches Density and mass profiles  -ray flux from  annihilation Galactic Center: Galactic Center: Flix, Klypin, Martinez, Prada, Simonneau

12. Galactic Center SGR A Point-like core Extended tail Similar 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

13. Dark matter annihilation ? 20 TeV Neutralino 20 TeV KK particle proposed before H.E.S.S. data proposed based on early H.E.S.S. data  J. Ripken ICRC 2005 Preliminary

14. Gamma ray spectrum Preliminary Unbroken power law, index 2.3 Preliminary Good agreement between HESS and MAGIC (large zenith angle observation).  Very unlikely to be dark matter.  Presence of a strong gamma-ray source outshines any possible DM signal

15. 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...

16. 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 HESS

17. Best targets for Dark Matter searches - Dwarf spheroidal galaxies with M/L ~ 100-200: DRACO · DRACO:  cul ~ 30º RA15 08.2 - DEC +67 23 D = 82 Kpc. CACTUS claim under scrutiny. Ursa Minor · Ursa Minor:  cul ~ 40º RA17 19.2 - DEC +57 58 D = 69 Kpc. DRACO 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.

18. - Dark Matter halo substructure: Best targets for Dark Matter searches - Compact High Velocity Clouds. (as “missing” satellites) - as gamma diffuse background. Anatoly Klypin Simulation of local group: ~300 satellites with V circ > 10 km/s

19. Dark Matter searches: conclusions VHE  -ray astronomy might provide WIMP annihilation signals but detection potential somewhat uncertain because :VHE  -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 -> important accelerator and relic density constraints but still too many possibilities open. Help from LHC ? - WIMP mass spectrum and couplings should be known to determine the annihilation probabilities into the different channels -> 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. - The cuspy region of the dark matter density profiles virtually unknown. - Background due to astrophysical sources. - Background due to astrophysical sources.

20. Dark Matter searches: conclusions GLAST catalogue together with VHE telescopes may be instrumental for DM searches: GLAST catalogue together with VHE telescopes may be 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 important to pinpoint DM signatures - 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:So far no confirmed detection and the enterprise to claim DM signals looks challenging but very important to continue because: => 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. => 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.

21. Cosmological measurements from VHE Gamma Ray absorption

22. 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 x x x  VHE  EBL  e + e - W.Hofmann

23. Optical Depth and GRH Then 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). High energy  -rays traversing cosmological distances are expected to be absorbed through their interactions with the EBL by: Where the Opacity  E,z  is:

25. M.Schroedter astro/ph-0504397 Present IACT range

26. CERN Courier June 2006

27. AGN Summary Source RedshiftTypeFirst DetectionConfimation M870.004FR IHEGRAHESS Mkn 4210.031BL LacWhippleMany Mkn 5010.034BL LacWhippleMany 1ES 2344+5140.044BL LacWhippleHEGRA Mkn 1800.045BL LacMAGIC 1ES 1959+6500.047BL LacTel. ArrayMany PKS 2005-4890.071BL LacHESS PKS 2155-3040.116BL LacMark VIHESS H1426+4280.129BL LacWhippleMany H2356-3090.165BL LacHESS 1ES 1218+3040.182BL LacMAGIC 1ES 1101-2320.186BL LacHESS PG 1553+113<0.78BL LacHESS-MAGICMAGIC  Reaching further out in redshift.

28. 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

30. Spectra & E xtragalactic B ackground L ight lower limits from galaxy counts measure- ments upper limits Reference shape HESS limits X X EBL resolved Universe more transparent

31. 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 ?).

32. GRH measurement is constraining the EBL density Blanch & Martinez 2004 Simulated measurements Different EBL models Mkn 421 Mkn 501 1ES 2344+514 Mkn 180 1ES1959+650 PKS 2155-304 H1426+428 PKS2005-489 1ES1218+304 1ES1101-232 H2356-309

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

34. 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). Whipple 2001

35. EBL constraint is paving the way for the use of AGNs to fit  M and    … Blanch & Martinez 2004 Simulated measurements Mkn 421 Mkn 501 1ES1959+650 Mkn 180 1ES 2344+514 PKS2005-489 1ES1218+304 1ES1101-232 H2356-309 PKS 2155-304 H1426+428

36. Determination of H 0,  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 ! MINOS We take the scenario where Ho is known from other experiments at the level of 4 km/ s Mpc (Hubble project).

37. 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.

38. Searching for energy dependence of the speed of light with IACTs

39. Tests of Lorenz Invariance Breaking effects. Quantum Gravity theories predict Lorentz Invariance breaking at very large energies. Large extra dimension theories predict a similar effect at much smaller energy scales O(1 TeV). L QG ~ O(L P ) =1.6 x 10 -35 m. E QG ~ O(M P ) = 1.22 x 10 19 GeV => Consequence: small LI violating terms modify free-field propagators  Different maximal attainable velocity for different particles: c e = c  (1+  ), 0 < abs(  ) << 1 Stecker and Glashow

40. 1.If  c e decay  -> e + e - kinematically allowed for gamma with energies above 2. If  >0 => c e > c  => electrons become superluminal for energies larger than E max /Sqrt(2) => Vacuum Cherenkov Radiation. - E  > 50 TeV from Crab Nebula => abs(  ) < 2 x 10 -16 E max = m e sqrt(2/abs(  )) - E e > 2 TeV from cosmic radiation => abs(  ) < 2 x 10 -14 - Modification of  e  e  threshold  Using Mkn 501 and Mkn 421 spectra observations up to E  > 20 TeV => abs(  ) < 1.3 x 10 -15

41. 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 E QG = O(M P )= O(10 19 ) GeV E QG = O(M P )= O(10 19 ) GeV

42. 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.

43. 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)

44. “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 E QE > M P /250 @ 95% CL The Whipple QG limit

45. 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  HE  IR -> e+ e- => shortening of the  ray horizon E QG =M P /100E QG =M P

46. 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