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Results From VERITAS

Results From VERITAS. K. Byrum High Energy Physics (HEP) Division Argonne National Laboratory. Indirect and Direct Detection of Dark Matter 6-12 Feb 2011, Aspen Colorado. Talk Outline. Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA.

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Results From VERITAS

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  1. Results From VERITAS K. Byrum High Energy Physics (HEP) Division Argonne National Laboratory Indirect and Direct Detection of Dark Matter 6-12 Feb 2011, Aspen Colorado

  2. Talk Outline Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA

  3. Very High Energy Gamma-ray Sky 1999 Crab first observed 1989 (Whipple)

  4. Very High Energy Gamma-ray Sky 2010 >130 sources

  5. Very High Energy Gamma-Ray Science: Astronomy, Astrophysics, Cosmology, Fundamental Physics • Search for Dark Matter & Fundamental Physics • Extragalactic Science (GRBs, Cosmology, AGNs, Starburst Galaxies) • Galactic Science (SNRs, PWNs, Binaries) This is a Broad Program

  6. Current status: Very High Energy Gamma-ray Detectors FGST HAWC (future) Milgro MAGIC VERITAS H.E.S.S.

  7. Talk Outline Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA

  8. VERITAS

  9. VHE Gamma-ray Technique • Multiple Telescopes: • improve angular resolution • improve energy resolution • reduce background • eliminate muons • improve stability

  10. VERITAS is currently the most sensitive TeV Observatory in the world. 500 MS/s Flash-ADC on every ch. 8-bit dual gain • Trigger & Readout: Three-level trigger • Constant fraction discriminator for each PMT • Pattern trigger on every telescope (requires hits on adjacent 3 PMTs within ~7-9ns) • Array trigger requires 2 or more telescopes

  11. Talk Outline Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA

  12. VERITAS: Indirect Dark Matter Program • Dark Matter makes up ~25% of energy budget of Universe WDMh2 = 0.113 (WMAP +BAO +SN1a) ~ 23% • DM has only been inferred gravitationally by its interaction with visible matter • Well described theoretically by extensions to standard model of particle physics (MSSM, Kaluza-Klein). • Cosmological constraints: Thermal relic of early universe with weak scale cross section & mass produces present DM density (Lee & Weinberg, 1977) • ~ 50 GeV/c2 < MWIMP < ~ 10 TeV/c2 • WIMP annihilation to g-rays: • g-ray line from direct annihilation (higher order process) • g-ray continuum from hadronization • Enhanced near MWIMP from internal brem

  13. Search for Indirect Detection of Dark Matter

  14. VERITAS Dark Matter Program • Concentrate on WIMP scenario: SUSY or Kaluza-Klein particle with mass in the GeV-TeV range • Assume pair annihilation giving rise to flux of g-rays w/cutoff at Mwimp • Expect g-ray flux proportional to squared DM density • Because of large uncertainties (WIMP mass, s, astrophysical flux),VERITAS observing strategy has been: “variety of targets” Target Disadvantages Advantages -Many astrophysical backgrounds -Huge uncertainities in the DM distribution (O(103)) -Closeby -Huge amount of DM Galactic Center -May be beyond reach of current instrument sensitivity -Can be tidally disrupted: uncertainties in the DM distribution O(10)) -DM dominated -Clear of astrophysical bkgd Dwarf spheroidal galaxies -Not DM dominated -Astrophysical backgorund -Interplay of baryons with DM not well known -Very close Globular clusters -Very far -Astrophysical background -Huge amount of DM Clusters of galaxies

  15. Indirect DM Search using Dwarf Spheroid • Recent discovery of many dSphs by SDSS; likely more discoveries in future VERITAS Dwarf Spheroid Targets: Draco, Ursa Minor, Bootes 1, Willman 1, Segue 1 18

  16. Indirect DM Search using Dwarf Spheroid • Dwarf galaxy observations made since early 2007 • Wobble pointing mode (0.5deg offset from camera center). • Second moment analysis (Hillas parameter of the shower image in the camera focal plane) for the selection of g-rays: cut optimized for a 3.5% Crab-like source • Reflected background model to subtract the residual background Typical map of null observation

  17. Indirect DM Search using Dwarf Spheroid No significant excess detected in any of the observations. aSignificance calculated using Li & Ma method (ApJ 272, 317 eqn.17) b95% CL upper limits using Rolke, Lopez & Conrad (arXiv:0403059v4) bounded profile likelihood method cAbove energy threshold, for a Crab-like spectrum

  18. Indirect DM Search using Dwarf Spheroid

  19. Indirect DM Search using Dwarf Spheroid • MSSM models from DarkSUSY within ±1 standard deviations of WMAP measured relic density. • Uncertainty ±1 order of magnitude due to systematics in halo modeling • 95% CL upper limits from Reflected Region Background Model analysis and Rolke zero-bounded profile likelihood • Boost factor from substructure, internal bremsstrahlung could give ×10-100 smaller <σv> X 100 ApJ 2010 Limits from VERITAS on annihilation <sv>: ~ 10-23 cm-3 s-1 By Matthieu Vivier

  20. VERITAS Future Dark Matter Analysis Continued observations on dSphs should reduce the theoretical uncertainties on mass models. Will target deeper exposures on select dSph targets Stacked analysis FERMI follow-up observations of DM source candidates Analysis currently underway Galactic Center Globular clusters Electron spectrum

  21. Talk Outline Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA

  22. VERITAS Upgrade Underway Motivation Increased effective area Better Background Suppression Better Angular Resolution Lower Energy Threshold Faster Slewing time Result is Improved Sensitivity • Faster detection for a given source strength • Detect weaker and more distant sources Components (started with T1 move in Summer 2009) • PMT replacement with higher QE PMTs • FPGA Level-2 pattern Trigger • Faster slewing for Telescopes After T1 move + mirror align 1% crab = 28 hr (already) After Trigger, High QE PMTs: 1% crab: ?

  23. Higher QE PMTs

  24. VERITAS FPGA Level 2 Trigger Upgrade Meant to be a drop in replacement to current aging L2 With enhanced capabilities Coincidence window improvement (down to 3-4ns) Pixel timing alignment Improved diagnostic capabilities Reconfigurable trigger through downloadable firmware Updates/improvements do not require access to hardware Alternate/experimental triggers may be tested w/o access to hardware All the hooks in place for adding a future L4 topological trigger First telescope installed parasitically Nov 2010; remaining telescopes in Summer 2011.

  25. Talk Outline Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA

  26. CTA

  27. VHE Gamma-ray Sensitivities: Present and Future FGST Energy (GeV) Space EAS IACT

  28. Sensitivities for WIMP detection “A significant region of parameter space could potentially be excluded (or the effort might result in a detection!) through observations of nearby dwarf galaxies. Therefore, increasing the sensitivity of atmospheric Cherenkov telescopes by another order of magnitude is our top priority for exploring the nature of dark matter” (Astro2010, Panel Report) x100 Exposure x10 Sensitivity x5 BG reduction E Threshold

  29. Summary VERITAS: Broad science program (that I didn’t discuss) Current Dark Matter program : Observations of 5 northern dSphs, with exposures 15 hrs No g-ray signal detected (so far) Limits on annihilation cross-sections of order 10-23-10-24 cm3 s-1; competitive with limits obtained by MAGIC and with southern dSphs by HESS Results using Draco, Ursa Minor, Willman 1 and Bootes 1 reported in ApJ Analysis of Galactic Center and Globular clusters underway VERITAS upgrade underway; expect improved sensitivity Future Dark Matter observations w/VERITAS: Upcoming observational data sets on dSphs will reduce the theoretical uncertainties on mass models and point to better dSph candidates Will target deeper exposures on select targets Will provided FERMI follow-up observations of DM source candidates Future Dark Matter observations with CTA Improved sensitivity of CTA order of magnitude beyond current instruments

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