Results From VERITAS K. Byrum High Energy Physics (HEP) Division Argonne National Laboratory...

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


Very High Energy Gamma-ray Sky 1999

Crab first observed 1989 (Whipple)


Very High Energy Gamma-ray Sky 2010

>130 sources


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)


Current status: Very High Energy Gamma-ray Detectors

H.E.S.S.

MAGIC

Milgro

FGST

HAWC (future)

VERITAS


Talk Outline



VERITAS


VHE Gamma-ray Technique

Multiple Telescopes: improve angular resolution improve energy resolution reduce background eliminate muons improve stability


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


Talk Outline



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


Search for Indirect Detection of Dark Matter


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


Indirect DM Search using Dwarf Spheroid

18

•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


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


Typical map of null observation



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



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


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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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: ?


Higher QE PMTs


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.


Talk Outline



CTA


VHE Gamma-ray Sensitivities: Present and Future

FGST

Energy (GeV)

Space IACT EAS


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


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

Results From VERITAS K. Byrum High Energy Physics (HEP) Division Argonne National Laboratory...

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