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Workshop on Exotic Physics with Neutrino Telescopes, Uppsala, 2006

Dark Matter Searches with Balloons and  -ray Telescopes Ullrich Schwanke (Humboldt University, Berlin). Workshop on Exotic Physics with Neutrino Telescopes, Uppsala, 2006. Overview. Indirect Dark Matter Searches Search for positron and antiproton signals The HEAT balloon experiment

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Workshop on Exotic Physics with Neutrino Telescopes, Uppsala, 2006

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  1. Dark Matter Searches with Balloons and -ray TelescopesUllrich Schwanke (Humboldt University, Berlin) Workshop on Exotic Physics with Neutrino Telescopes, Uppsala, 2006

  2. Overview • Indirect Dark Matter Searches • Search for positron and antiproton signals • The HEAT balloon experiment • Gamma-ray Astronomy • 511 keV annihilation line (Integral) • Diffuse galactic gamma-ray emission (EGRET) • {Extragalactic gamma-ray background (EGRET)} • Gamma-rays from the Galactic centre (H.E.S.S.) • Summary and Outlook

  3.  GLAST Simulation Indirect Searches • Extraterrestrial sources. Detection in orbit/atmosphere. • Potentially large amount of DM (~entire Universe). • Competition from less exotic production mechanisms. • Modelling of Milky Way required. • Antiprotons • Propagation effects • Expect energy spectrum with cut-off at mass of DM particle • Positrons • lower range than antiprotons • Gammas • Directional information can be correlated with (dark) matter density in the Milky Way • Gamma-line(s) would be unique signature.

  4. Search for Antiprotons and Positrons • Historic claims for a sizable fraction of positrons/antiprotons in the cosmic radiation • Experimental challenge: small fraction of e+/p-, wealth of background with opposite charge • Good particle ID required 1987 BESS, CAPRICE, High-Energy Antimatter Telescope, ... HEAT BESS

  5. HEAT Positron Fraction 1987 HEAT-pbar • Measured by two different detectors (HEAT-e and HEAT-pbar) • Near solar maximum (1994 and 1995) and solar minimum (2000) • Different vertical geomagnetic cutoffs: ~1 GeV (1995) and ~4 GeV (1994, 2000) • Statistical significance ? Interpretation ?

  6. Interpretation of the Positron Fraction • Neutralino DM • inefficient generation of positrons • increase annihilation rate by clumping • Kaluza-Klein Dark Matter • viable positron source for mass range 300..400 GeV e+ diffusion parameters D. Hooper, hep-ph/0409272 (Annihilation rate normalized to data)

  7. Antiproton Fraction and Flux 1987 • Some claimed excesses in the past • Now, measurements seem to be consistent with purely secondary production of antiprotons • Expect BESS 2004 data (factor ~10 longer flights) Primary antiproton flux from annihilation of a 964 GeV MSSM neutralino (P. Ullio, astro-ph/9904086 (1999))

  8. Gamma-Ray Telescopes Soft -rays: < 1 MeV Integral Very high energy -rays: > 100 GeV Air-Cherenkov Telescopes H.E.S.S. Whipple/Veritas MAGIC CANGAROO High energy -rays: 10 MeV – 100 GeV EGRET, GLAST

  9. Galactic 511 keV Annihilation Line • Accurate tracer of galactic positrons. • Thermalization of positrons required. • Various detections since initial discovery in 1973. • Agreement on absolut flux, no time dependence • Morphology less clear (halo + galactic disk component) e+e-

  10. Latest Data: Integral and SPI launched in Oct 02 • SPectromètre Integral • 16° FoV (FWHM) • 20 keV – 10 MeV • 2 keV energy resolution (at 1 MeV) • 2° angular resolution

  11. Observations of the Galactic Centre Exposure 20  Energy (keV) • Measurement relies on accurate subtraction of instrumental annihilation line • Flux and intrinsic line width compatible with earlier measurements

  12. 0.00 photons/cm2/s/sr 0.04 Source Morphology 15 kpc DIRBE • Gaussian with FWHM=9°

  13. Interpretations (I) • Conventional Interpretations • Supernovae • Wolf-Rayet Stars • Neutron stars, pulsars • Cosmic rays • ...and (of course) Black holes • Dark Matter Interpretation • C. Boehm et al., astro-ph/0309686 • F. Beacom et al., astro-ph/0409403 Contribution from disk expected, i.e. smaller bulge-to-disk ratio (Integral: B/D > 0.3..0.5)

  14. Flux()/Flux(0) Interpretations (II) • DM annihilation occurs „invisibly“ • Light (1-100 MeV) scalar DM particles • Exchange particle could be fermion (with suppressed Z couplings) or new gauge boson („U boson“) • Correct DM relic density is obtained • Caveat: COMPTEL and EGRET data require m<20 MeV when internal bremsstrahlung is taken into account • Cannot be excluded....

  15. Gamma-Ray Telescopes Soft -rays: < 1 MeV Integral Very high energy -rays: > 100 GeV Air-Cherenkov Telescopes H.E.S.S. Whipple/Veritas MAGIC CANGAROO High energy -rays: 10 MeV – 100 GeV EGRET, GLAST

  16. Diffuse Gamma-Ray Emission CGRO (1991-2000) • EGRET • 20 MeV – 30 GeV • energy resolution 20% • angular resolution: • 1.3° at 1 GeV • 0.4° at 10 GeV

  17. EGRET Gamma-Ray Data • Subtraction of 271 EGRET point sources  Diffuse galactic gamma-ray emission remains • Excess observed from all directions • Right now, EGRET data (and more) can be described by scenarios with and without DM S. D. Hunter et al. Astrophys. J. 481, 205 (1997) Solution without DM: Strong, Moskalenko & Reimer, Astrophys. J. 613, 962 (2004) Solution with DM: W. de Boer et al., A&A 444 (2005) 51.

  18.  Geometry  Diffusion GALPROP: Cosmic Ray Propagation • radiation field • nuclear reaction networks • spatial distribution of sources • energy spectra at injection • solar modulation Model

  19. 1) Solution without Dark Matter (30.5°<l<179.5°, 180.5°<l<330.5°) 0 decay 1.0-2.0 GeV Inverse Compton Bremsstrahlung Extragalactic Gamma-Ray Background • GALPROP: Numeric evaluation of Diffusion-Loss-Equations. • Obtains (anti)proton and electron/positron spectra, too. • -ray data can be described fairly well, albeit at the expense of a slightly worse matching of the local electron and proton spectra

  20. 2) Solution with Dark Matter • Explains EGRET data with a photon component from neutralino annihilation • Gets background shape from GALPROP, signal shape from SUSY generators • Determines halo structure, needs two rings of stars around Milky Way • Locates WIMP mass in 50-100 GeV range • DM signal compatible with supersymmetry for boost factors of ~20 (-30°<l<+30°) E>0.5 GeV Neutralino annihilation Backgrounds

  21. Gamma-Ray Telescopes Soft -rays: < 1 MeV Integral Very high energy -rays: > 100 GeV Air-Cherenkov Telescopes H.E.S.S. Whipple/Veritas MAGIC CANGAROO High energy -rays: 10 MeV – 100 GeV EGRET, GLAST

  22. Crab 1989 H.E.S.S. 2004 1 year Cas A 2002 1 night 30 sec EGRET H.E.S.S. Performance The Crab Nebula • Trigger threshold: 40 – 100 GeV • Angular resolution is a few arcminutes (~0.1°, stereo) • Collection area: 50000 m2 • Relative energy resolution ~20% • Factor 102 improved sensitivity • Duty cycle: 1000 h per year

  23. Observations of the Galactic Centre H.E.S.S. Field of View (5°)

  24. 3‘ Sgr A* Sgr A East The Dynamical Centre:Sgr A* • 3  106 solar mass black hole • Very low luminosity • Highly variable non-thermal emission in IR and X-ray • Surrounded by supernova-remnant Sgr A East and H II region Sgr A West MPE / R. Genzel et al.

  25. H.E.S.S. Result (2003) • 17 hours of data • Taken with 2 telescopes during construction of the array • 160 GeV threshold • 11 signal from close to Sgr A* • Point-like source • See A&A 425, L13-16 (2004)

  26. H.E.S.S. Result (2004) G0.9+0.1 • G0.9 ist SNR mit Pulsarwind-Nebel • Starkes Signal vom Galaktischen Zentrum HESS J1745-290

  27. Chandra GC survey NASA/UMass/D.Wang et al. Chandra GC survey NASA/UMass/D.Wang et al. CANGAROO (80%) CANGAROO (80%) H.E.S.S. H.E.S.S. (95%) Whipple (95%) Whipple (95%) Contours from Hooper et al. 2004 Position

  28. H.E.S.S. 95% 68% Chandra F. Banagoff et al. Position: Compatible with Sgr-A*

  29. Energy Spectrum • HESS: dN/dE  E-2.2 • Flux > 160 GeV: 5 % of Crab flux • CANGAROO: dN/dE  E-4.6 Flux > 160 GeV: ~ 1 Crab

  30. H.E.S.S. 2004 Data • Two years of data: 40 h with full 4 telescope array • Significance of HESS J1745-290 is 35 s • Position, flux and spectrum (~2.3) compatible • No Variability on scales of • Years • Months • Days • Minutes

  31. Interpretations of the TeV Signal from the Galatic Centre Particle Acceleration near the Black Hole Sgr A*: F. Aharonian & A. Neronov, astro-ph/0408303 (2004); Atoyan & Dermer, astro-ph/0401243 (2004). Particle Acceleration in the supernova remnant Sgr A East: Crocker et al. astro-ph/0408183 (2004) Dark Matter Annihilation: D. Horns, astro-ph/0408192; Bergström et al., astro-ph/0410359

  32. 1) Particle Acceleration close to Sgr A* • Low luminosity of Sgr A*  ~10 TeV photons can escape without e+e- conversion • There is evidence that Sgr A* is spinning at a good fraction of the maximum possible speed. • Rotation in a magnetic field produces a strong electro-motoric force • Acceleration of protons to 1018 eV (?) • VHE gamma-rays via curvature radiation or hadronic interactions • Acceleration of electrons (?) • TeV Gamma-rays via Inverse Compton Scattering • More efficient than proton acceleration • Or acceleration at shocks in the accretion disk • TeV radiation via: p + p p+/-, p0gg

  33. Log E (eV) VHE g-rays from Sgr A* ? Aharonian et al. 2004 • Data can be explained as radiation of accelerated protons… or electrons close (<10 Rg) to Sgr A* • Absence of variability does not support BH origin of -rays

  34. 2) Particle Acceleration in Sgr A East • Spectral index measured by H.E.S.S. close to expectation from Fermi acceleration • Sgr A East is a powerful SNR • 10,000 years old • Compact (~3 arcmins) • Energy: 4 x 1052 erg • Crocker et al. explain overabundance of cosmic rays from the GC around 1018 eV • Flux normalization from H.E.S.S. (or a nearby EGRET source) under the assumption of pp induced p0 decay • Explains particle acceleration up to the ankle (3 1018 eV) • Note: SUGAR/AGASA CR anisotropies are constrained by AUGER data

  35. Association with CR Anisotropy? Crocker et al 2004, astro-ph/0408183 EGRET p+p  0+X  n+X Log (dF/dE / cm-2 s-2 eV-1) Fit H.E.S.S. AGASA (1018 eV) Log (E/eV) No indication for CR anisotropies in AUGER data, but plausible explanation for H.E.S.S. data

  36. 3) DM Interpretation: Spectrum • CANGAROO Spectrum consistent with a 1.1 TeV neutralino-type WIMP • HESS Spectrum requires a mass > 12 TeV • Most models favour a < 2 TeV WIMP • Requires high DM density and/or cross section • Kaluza-Klein DM requires large boost factors (>103) • DM interpretation is stretched further by H.E.S.S. 2004 data Wimp annihilation spectra have a cutoff at ~(0.2…0.3) M

  37. Summary and Outlook • There is no WIMP that can explain more than one measurement…. • For antiprotons and positrons, future space-borne experiments (AMS02, Pamela) will do a lot better than balloon experiments. • 511 keV line: Interpretation? • Galactic Centre region • Multi-wavelength approach • Continue identifying and subtracting conventional sources • GLAST (5/2007) and low-threshold IACTs will provide improved sensitivity below 100 GeV • Search for gamma-lines and continuum. • Observation of other DM candidates (e.g. dwarf galaxies orbiting the Milky Way) PAMELA GLAST

  38. Extragalactic -ray background (EGB) • Various contributions: Seyfert galaxies, quasars, type 1a supernovae... • Re-analysis of complete EGRET data set found that galactic background (from GALPROP) was underestimated (i.e. EGB overestimated) 1998 1 GeV

  39. EGB and Dark Matter • Re-analysis of complete EGRET data set, GALPROP for foreground subtraction • D. Elsässer and K. Mannheim, PRL 94, 171302 (2005) • Annihilation of a MSSM neutralino in NFW-type DM halos • Integration from z=20 to present, factor 106 enhance due to structure formation • Gaugino-line WIMP with mass 515+110-75 GeV

  40. Caveats • S. Ando, PRL 94, 171303 (2005) • Assume universality of halo density profile, same WIMP mass and cross-section • Use EGRET, H.E.S.S. and CANGAROO galactic centre data as upper limit on the neutralino flux and predict EGB • If DM component in EGB is real, it would imply a much higher flux from the Galactic Centre • 515 GeV WIMP is at odds with DM interpretation of galactic EGRET data

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