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Probing Dark Matter and pre-Galactic Lithium with Hadronic Gamma Rays

Probing Dark Matter and pre-Galactic Lithium with Hadronic Gamma Rays. Tijana Prodanović University of Illinois at Urbana-Champaign Brian D. Fields, UIUC John F. Beacon, OSU. Outline. Cosmic Rays & Gamma Rays Diffuse Hadronic Galactic Gamma Rays What we know

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Probing Dark Matter and pre-Galactic Lithium with Hadronic Gamma Rays

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  1. Probing Dark Matter and pre-Galactic Lithium with Hadronic Gamma Rays Tijana Prodanović University of Illinois at Urbana-Champaign Brian D. Fields, UIUC John F. Beacon, OSU

  2. Outline • Cosmic Rays & Gamma Rays • Diffuse Hadronic Galactic Gamma Rays • What we know • What we don’t know: dark matter signal? • Diffuse Hadronic Extragalactic Gamma-Ray Background • Lithium-gamma-ray connection • Probe lithium nucleosynthesis • Structure Formation Cosmic Rays • Implications • Constraints • Conclusion Seminar @ North Carolina State University 12/13/2005

  3. Cosmic Rays • High-energy charged particles • Accelerated in astrophysical (collisionless) shocks • Spectrum: • Strong shocks: Flux~E-2 • Measured (JACEE 1998) : Flux~E-2.75 • CR proton energy density in local interstellar medium: ~0.83 eV/cm3 (typical galactic magnetic field B~3μGauss has ε~0.25 eV/cm3) • Trivia: CR muon flux at sea level 1 cm-2 min-1 Seminar @ North Carolina State University 12/13/2005

  4. Any shock source is a candidate! (Blandford & Eichler 1987) Sites Supernova remnants (Blondin, Reynolds, McLaughlin) galactic cosmic rays (D. Ellison) Structure formation shocks structure formation cosmic rays (Inoue, Kang, Miniati) Cosmic Ray Acceleration Sites VLA image of Tycho SNR Reynolds & Chevalier Seminar @ North Carolina State University 12/13/2005

  5. Why Cosmic Rays? • Galaxy/Universe is a “beam dump” for CRs ! • Probe acceleration sites • Probe particle physics beyond our reach • Probe dark matter (WIMP annihilation) • Understand processes difficult to access • Structure formation shock properties • Cosmological baryons • But CRs diffuse in the magnetic field… Seminar @ North Carolina State University 12/13/2005

  6. Gamma Rays … • give away direction! • “Pionic” gamma-rays • Distinctive spectrum – pion “bump”; peaks at mπ/2 (Stecker 1971; Dermer 1986) • But no strong evidence for pion “bump” • Can use the shape of the spectrum (Pfrommer & Enßlin 2003) to find max “pionic” fraction (Prodanović & Fields 2004) • Relativistic electrons • Inverse Compton (off starlight & CMB) • Synchrotron • Bremsstrahlung Seminar @ North Carolina State University 12/13/2005

  7. Seminar @ North Carolina State University 12/13/2005

  8. 1. Galactic Cosmic Rays: 1.1 Galactic Gamma-Ray Sky Gaetz et al (2000) SNR E0102-72

  9. Galactic “Pionic” Gamma Rays Prodanović and Fields (2004a) • Find max “pionic” fluxso that “pion bump” stays below observed Galactic spectrum • Galactic CRs: • Max “pionic” fraction • But notice the residual! Brems/IC Strong et al. (2004) Seminar @ North Carolina State University 12/13/2005 ???

  10. Constraining Dark Matter • Possible dark matter annihilation gamma-ray signals • But first need to constrain gamma-ray foreground • Boer et al. 2005 (astro-ph/0508617) : “GeV excess” due to WIMP annihilation, mass ~ 50-100 GeV • Such signal requires low “pionic” component Seminar @ North Carolina State University 12/13/2005

  11. Constraining Dark Matter Foreground Prodanović, Fields & Beacom (2005) In preparation • Though inverse compton component at low end, cutoff at ~ TeV • Pionic gamma’s dominate? • Unconventional spectral index • Milagro: pionic dominates indeed • Observed spectral index • Milagro: pionic only ~10% ! • Another component? Dark matter? Point sources? Need more data!!!! Milagro Water Cherenkov Detector Seminar @ North Carolina State University 12/13/2005

  12. Beck et al. 1994 1. Galactic Cosmic Rays:1.2 Extragalactic Gamma-ray Background

  13. Li-g-ray Connection • Any cosmic-ray source produces both gamma-rays and lithium • Connected essentially with ratio of reaction rates (Fields and Prodanović 2005) • Li abundance: local CR fluence • Diffuse extragalactic : CR fluence across Universe • Given one, constrain other Seminar @ North Carolina State University 12/13/2005

  14. Extragalactic Gamma-Ray Background • Still emission at the Galactic poles • Subtract the Galaxy EGRB is the leftover(Strong 2004, Sreekumar 1998) • Guaranteed components(Pavlidou & Fields 2002) • Normal galaxies • Blazars(Stecker & Salamon 1996) • Any other cosmic-ray source Seminar @ North Carolina State University 12/13/2005

  15. Estimating Galactic CR “pionic” g-rays from Extragalactic Gamma-Ray Background • “Pion bump” not observed in extragalactic gamma-ray background • Maximize pionic spectrum so that it stays below the observed extragalactic gamma-ray background • Galactic CRs – accelerated in supernova remnants; use propagated spectrum • Integrate over the redshift history of Galactic CR sources (cosmic star-formation rate) • Max “pionic” fraction Fields and Prodanović (2005) Seminar @ North Carolina State University 12/13/2005

  16. Galactic CRs and 6Li • 6Li only made by cosmic rays • Standard assumption: 6LiSolarmade by Galactic CRs • Li-gamma-ray connection: 6LiSolar requires → but entire observed extragalactic gamma-ray background(Strong et al. 2004) • What’s going on? • Milky Way CR flux higher than average galaxy? • CR spectrum sensitivity (thresholds!; Li probes low E) • 6Li not from Galactic CRs? Seminar @ North Carolina State University 12/13/2005

  17. The “Lithium Problem” • 7Li made predominantly in the Big Bang Nucleosynthesis (Cyburt, Fields, McLaughlin, Schramm) • Measurements in low-metallicity halo stars: lithium plateau (Spite & Spite 1982) → indicate primordial lithium • But WMAP (2003)result: primordial Li~ 2 times higher than observed in halo-stars lithium problem • Any pre-Galactic sources of Li would contribute to halo-stars and make problem even worse! • And then there were cosmological cosmic rays… Cyburt 2005 (private communication) Seminar @ North Carolina State University 12/13/2005

  18. 2. Structure Formation Cosmic Rays: Extragalactic Gamma-Ray Background Miniati et al. 2000

  19. Structure formation shocks - cosmological shocks that arise from baryonic infall and merger events during the growth of large-scale structures (Miniati) Diffusive shock acceleration mechanism structure formation/cosmological cosmic rays X-ray observations of galaxy clusters: non-thermal excess(see eg. Fusco-Femiano et al. 2004) A large reservoir of energy and non-thermal pressure Miniati et al. 2000 Structure Formation Cosmic Rays Seminar @ North Carolina State University 12/13/2005

  20. How To Find Them? • Implications still emerging • Will contribute to extragalactic gamma-ray background (Loeb & Waxman 2000) • CRs make LiBeB (Fields, Olive, Ramaty, Vangioni-Flam) • But structure formation CRs are mostly protons and α-particles → only LiBeB • Will contribute to halo star Li abundance → “Li problem” even worse! (Suzuki & Inoue 2002) • Use Li-gamma-connection as probe Seminar @ North Carolina State University 12/13/2005

  21. Estimating SFCR“pionic” g-rays from Extragalactic Gamma-Ray Background • Structure Forming Cosmic Rays – assume all come from strong shocks with spectrum (about the same source spectrum as for Galactic CRs, but does not suffer propagation effects) • Assume all pionic g-rays are from structure formationCRs and all come from single redshift (unlike for Galactic CRs, history not known in this case) • Max “pionic” fraction z=0 z=10 Prodanović and Fields(2004a) Seminar @ North Carolina State University 12/13/2005

  22. Structure Formation CRs and Lithium • Use Li-gamma-ray connection • From observed extragalactic gamma-ray background estimate maximal pionic contribution, assign it to structure formation CRs → estimate LiSFCR production (depending on the assumed redshift) • Structure formation CRs can be potentially significant source of pre-Galactic Lithium! • Need constrain structure formation CRs Seminar @ North Carolina State University 12/13/2005

  23. Searching for SFCRs in High Velocity Clouds • Clouds of gas falling onto our Galaxy (Wakker & van Woerden 1997) • Some high-velocity clouds have metallicity 10% of solar • Some high-velocity clouds show evidence for little or no dust • Origins: • Galactic fountain model(Shapiro & Field 1976) • Extragalactic • Magellanic Stream-type objects or • gas left over from formation of the Galaxy(Oort, Blitz , Braun) low-metallicity, HVCs with little dust are promising sites for testing pre-Galactic Li and SFCRs(Prodanović and Fields 2004b) Seminar @ North Carolina State University 12/13/2005

  24. New Data on the Way! • GLAST: • A view into “unopened window” (up to 300 GeV) • Better extragalactic background determination • Pion feature? • Cherenkov experiments: TeV window • H.E.S.S. • Southern hemisphere • Observing since 2004 • VERITAS • Northern hemisphere • upcoming H.E.S.S. Collaboration Science 309 (2005) 746 Seminar @ North Carolina State University 12/13/2005

  25. Final Thoughts… • Universal, model independent approach: pionic spectrum • Probe both Galactic and extragalactic sourcs • Li-gamma connection • Need to disentangle diffuse gamma-ray sky! • Probe CR populations and implications through their diffuse gamma-ray signatures • A foreground for possible dark matter signal • Structure Formation Cosmic Rays • A large energy reservoir • Can have important effects (e.g. even worse lithium problem) • The key: need to use different measurements in concert (e.g. TeV measurements: lever arm on pionic component) Seminar @ North Carolina State University 12/13/2005

  26. The End Seminar @ North Carolina State University 12/13/2005

  27. Strong et al. (2004) Diffuse Galactic continuum, EGRET data Conventional model Optimized model Seminar @ North Carolina State University 12/13/2005

  28. BBN in the light of WMAP Dark, shaded regions = WMAP+ BBN predictions Light, shaded and dashed regions = observations Cyburt, Fields and Olive (2003) Seminar @ North Carolina State University 12/13/2005

  29. Detecting TeV Gammas • EM air shower: • ~TeV gamma’s hit top of the atmosphere • → pair production; Compton Scat. + Bremsstrahlung → high-energy gamma’s → pair production … = electron + photon cascade • Cherenkov light • Particle travels “superluminously” • “Pool” of faint bluish light (~250m diameter) • For 1 TeV photon: 100 photons/m2 • Extensive air shower detectors: • Air Cherenkov: reflectors • Eth~200 GeV, small f.o.v., short duty cycle • Air Shower Array: scintillators • Eth~50 TeV, large f.o.v., long duty cycle H.E.S.S. Seminar @ North Carolina State University 12/13/2005

  30. Cherenkov Radiation: Gamma-ray vs. Hadronic More narrow cone! Seminar @ North Carolina State University 12/13/2005

  31. Milagro Gamma-Ray Observatory • Miracle telescope@ LANL • Water CherenkovExtensive Air Shower Array: • Low threshold • Large field of view • Observing24/7 • Cherenkovlight threshold • lower in the water • Gamma’spair-produce faster • 450 + 273PMTs TeV Gamma-Ray Fishing! Seminar @ North Carolina State University 12/13/2005

  32. Seminar @ North Carolina State University 12/13/2005

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