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

Tijana Prodanović North Carolina State University 12/13/2005 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

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

Tijana Prodanović North Carolina State University 12/13/2005 Cosmic Ray Acceleration Sites 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) VLA image of Tycho SNR Reynolds & Chevalier

Tijana Prodanović North Carolina State University 12/13/2005 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…

Tijana Prodanović North Carolina State University 12/13/2005 Gamma Rays …  give away direction!  “Pionic” gamma-rays  Distinctive spectrum – pion “bump”; peaks at m π /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

Tijana Prodanović North Carolina State University 12/13/2005

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

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

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

Tijana Prodanović North Carolina State University 12/13/2005 Constraining Dark Matter Foreground  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? Prodanović, Fields & Beacom (2005) In preparation Milagro Water Cherenkov Detector Need more data!!!!

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

Tijana Prodanović North Carolina State University 12/13/2005 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

Tijana Prodanović North Carolina State University 12/13/2005 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

Tijana Prodanović North Carolina State University 12/13/2005 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)

Tijana Prodanović North Carolina State University 12/13/2005 Galactic CRs and 6 Li 6 Li only made by cosmic rays Standard assumption: 6 Li Solar made by Galactic CRs Li-gamma-ray connection: 6 Li Solar 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)  6 Li not from Galactic CRs?

Tijana Prodanović North Carolina State University 12/13/2005 The “Lithium Problem” 7 Li 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)

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

Tijana Prodanović North Carolina State University 12/13/2005 Structure Formation Cosmic Rays 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

Tijana Prodanović North Carolina State University 12/13/2005 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

Tijana Prodanović North Carolina State University 12/13/2005 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 formation CRs 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)

Tijana Prodanović North Carolina State University 12/13/2005 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 Li SFCR production (depending on the assumed redshift ) Structure formation CRs can be potentially significant source of pre-Galactic Lithium! Need constrain structure formation CRs

Tijana Prodanović North Carolina State University 12/13/2005 Searching for SFCRs in High Velocity Clouds  Clouds of gas falling onto our Galaxy (Wakker & van Woerden 1997)  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)  Some high-velocity clouds have metallicity 10% of solar low-metallicity, HVCs with little dust are promising sites for testing pre-Galactic Li and SFCRs (Prodanović and Fields 2004b)

Tijana Prodanović North Carolina State University 12/13/2005 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

Tijana Prodanović North Carolina State University 12/13/2005 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)

Tijana Prodanović North Carolina State University 12/13/2005 The End

Tijana Prodanović North Carolina State University 12/13/2005 Strong et al. (2004) Diffuse Galactic continuum, EGRET data Conventional modelOptimized model

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

Tijana Prodanović North Carolina State University 12/13/2005 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/m 2  Extensive air shower detectors:  Air Cherenkov: reflectors  E th ~200 GeV, small f.o.v., short duty cycle  Air Shower Array: scintillators  E th ~50 TeV, large f.o.v., long duty cycle H.E.S.S.

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

Tijana Prodanović North Carolina State University 12/13/2005 Milagro Gamma-Ray Observatory  Miracle LANL TeV Gamma-Ray Fishing!  Water Cherenkov Extensive Air Shower Array:  Low threshold  Large field of view  Observing 24/7  Cherenkov light threshold  lower in the water  Gamma’s pair-produce faster  PMTs

Tijana Prodanović North Carolina State University 12/13/2005