Results From VERITAS K. Byrum High Energy Physics (HEP) Division Argonne National Laboratory Indirect…
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Results From VERITAS
K. ByrumHigh Energy Physics (HEP) Division
Argonne National Laboratory
Indirect and Direct Detection of Dark Matter 6-12 Feb 2011, Aspen Colorado
2 Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
Talk Outline
Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA
3 Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
Very High Energy Gamma-ray Sky 1999
Crab first observed 1989 (Whipple)
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Very High Energy Gamma-ray Sky 2010
>130 sources
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Very High Energy Gamma-Ray Science:Astronomy, Astrophysics, Cosmology, Fundamental
Physics
This is a Broad Program
Search for Dark Matter & Fundamental Physics Extragalactic Science (GRBs, Cosmology, AGNs, Starburst Galaxies)Galactic Science (SNRs, PWNs, Binaries)
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Current status: Very High Energy Gamma-ray Detectors
H.E.S.S.
MAGIC
Milgro
FGST
HAWC (future)
VERITAS
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Talk Outline
Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA
8 Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
VERITAS
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VHE Gamma-ray Technique
Multiple Telescopes: improve angular resolution improve energy resolution reduce background eliminate muons improve stability
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VERITAS is currently the most sensitive TeV Observatory in the world.
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
500 MS/s Flash-ADC on every ch. 8-bit dual gain
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13 Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
14 Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
Talk Outline
Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA
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VERITAS: Indirect Dark Matter Program
Dark Matter makes up ~25% of energy budget of Universe
DMh2 = 0.113 (WMAP +BAO +SN1a) ~ 23%DM has only been inferred gravitationally by its interaction with visible matterWell 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 -rays:-ray line from direct annihilation (higher order process)-ray continuum from hadronizationEnhanced near MWIMP from internal brem
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Search for Indirect Detection of Dark Matter
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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 -rays w/cutoff at Mwimp
• Expect -ray flux proportional to squared DM density
Because of large uncertainties (WIMP mass, , astrophysical flux), VERITAS observing strategy has been: “variety of targets”
Target
Advantages
Disadvantages
Galactic Center
Dwarf spheroidal galaxies
Globular clusters
Clusters of galaxies
-Closeby-Huge amount of DM
-Many astrophysical backgrounds-Huge uncertainities in the DM distribution (O(103))
-DM dominated-Clear of astrophysical bkgd
-Very close
-Huge amount of DM
-May be beyond reach of current instrument sensitivity -Can be tidally disrupted: uncertainties in the DM distribution O(10))-Not DM dominated-Astrophysical backgorund-Interplay of baryons with DM not well known-Very far-Astrophysical background
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Indirect DM Search using Dwarf Spheroid
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•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
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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 -rays: cut optimized for a 3.5% Crab-like sourceReflected background model to subtract the residual background
Indirect DM Search using Dwarf Spheroid
Typical map of null observation
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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 methodcAbove energy threshold, for a Crab-like spectrum
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Indirect DM Search using Dwarf Spheroid
22 Indirect and Direct Detection of Dark Matter, 6-12 Feb, 2011, K.Byrum
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>
Limits from VERITAS on annihilation <v>: ~ 10-23 cm-3 s-1
X 100ApJ 2010
By Matthieu Vivier
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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
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Talk Outline
Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA
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VERITAS Upgrade UnderwayMotivation
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: ?
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Higher QE PMTs
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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.
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Talk Outline
Introduction VERITAS VERITAS Results VERITAS Upgrade Beyond VERITAS: CTA
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CTA
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VHE Gamma-ray Sensitivities: Present and Future
FGST
Energy (GeV)
Space IACT EAS
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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 Exposurex10 Sensitivityx5 BG reductionE Threshold
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Summary VERITAS: Broad science program (that I didn’t discuss) Current Dark Matter program :
– Observations of 5 northern dSphs, with exposures 15 hrs– No -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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