VHE Gamma Ray Astronomy: a UK strategy for the next decade Paula Chadwick for the University of Durham Johannes Knapp for the University of Leeds Richard Holdaway & John Womersley for RAL Definitions & detection The international context Some recent highlights The UK situation Our proposed strategy

(Multiple) Images of showers Gamma rays form consistent pattern Excellent gamma-hadron separation (~100%) Showers located to ~0.1° at threshold Point source location to ~ 20” Imaging Atmospheric Cherenkov Technique VHE gamma rays can be defined as those detectable from the ground using the: Generally E > 100 GeV at present

Current Major IACTs N tels EtEt Res.FoV Dead Time Sens. CANGAROO III 3X ✓✓✓ X H.E.S.S. 4 ✓✓✓✓✓✓ MAGIC 1 ✓✓✓✓✓ VERITAS 4 ✓✓✓✓✓✓

Science topics Dunkle Materie Pulsars and PWN GRBs SNRs AGNs Origin of cosmic rays Cosmology Dark matter Space-time & relativity

VERITAS-4 Four 12m diameter telescopes Davies-Cotton design, 345 mirrors FoV 3.5° 499 PMTs, pixel spacing 0.15° Two telescopes operating in stereo mode Four telescope array by end 2006 USA: Smithsonian Astrophysical Observatory; Iowa State University;University of California, Los Angeles; University of Chicago; University of Utah; Washington University, Saint Louis UK: Leeds University Canada: McGill University Ireland: National University of Ireland Integrated Pulse

First Stereo Observations Markarian 421 at ~ 2 Crab in Jan/Feb 2006

High Energy Stereoscopic System – H.E.S.S. Four 13m diameter telescopes Davies-Cotton design, m diameter mirrors FoV 5° 960-pixel cameras Routine operations since January 2004 Germany: M-PIK Heidelberg; Humboldt University, Berlin; University of Hamburg; Ruhr University, Bochum; Landessternwarte Heidelberg France: LLR Ecole Polytechnique, LPNHE, PCC College de France, University of Grenoble, CERS Toulouse, CEA Saclay, Observatoire de Paris-Meudon, University of Montpellier II UK: Durham University Ireland: Dublin Institute for Advanced Studies Czech Republic: Charles University, Prague Armenia: Yerevan Physics Institute Namibia: University of Namibia South Africa: North-Western University

Progress in VHE Gamma Rays… Source Type Pulsar wind nebula (Crab, MSH15-52…)16 SNRs (Cas A, RXJ1713….)26 Binary Pulsar (PSR B )01 Microquasar (LS5039)01 Diffuse (Cygnus region)01 AGN (PKS , Mkn 421…)711 Unidentified26 TOTAL1232 X 7 X 11 X 40 X 12 X 2

RXJ Aharonian et al., Nature, 75, 432 (2004) 2 telescopes with/without array trigger E > 800 GeV; angular res. 3 arcmin hours livetime, 20  Enomoto, R. et al.,Nature, 416, (2002) Image from 2004 with all four H.E.S.S. Phase telescopes; 2 arcmin resolution, 33 hours livetime.

Vela region Vela (Rosat) Vela Junior d ≈200 pc age ≈ 700 y

H.E.S.S. observations show a source which is consistent with the position of Sgr A* and with a nearby SNR. Significance with 2004 data > 30  Aharonian et al., Astron. Astrophys., 425, L13 (2004) Galactic Centre

Dark matter annihilation? 20 TeV Neutralino 20 TeV KK particle proposed before H.E.S.S. data proposed based on early H.E.S.S. data Preliminary Bergström et al, Phys. Rev. Lett., 94, id (2005)

Diffuse Emission

Galactic Plane Scan

1ES Z = H (x 0.1) Z = EBL Source spectrum  = 1.5 Preliminary AGN Spectra & E xtragalactic B ackground L ight

1 ES 1101  = 2.9±0.2 H 2356 (x 0.1)  = 3.1±0.2 too much EBL Source spectrum  Upper limit on EBL Preliminary

Spectra & E xtragalactic B ackground L ight 1 ES 1101  = 2.9±0.2 H 2356 (x 0.1)  = 3.1±0.2 too much EBL Not really a solution: add huge amount of UV photons to EBL  problems with source energetics, X-ray/gamma- ray SED ratio UV EBL Preliminary

Spectra & E xtragalactic B ackground L ight lower limits from galaxy counts measure- ments upper limits Reference shape HESS limits X X EBL resolved Universe more transparent

Cosmic Background – hidden quasars MWB XRB IRB Cosmic Stars/AGN AGN X

The UK VHE Gamma Ray Scene A long UK history in VHE gamma ray astronomy Two UK groups – Leeds (VERITAS) and Durham (H.E.S.S.) Both provide a strong contribution to their respective collaborations based on over 20 years’ experience UK thus has access to data from both North and South, but our efforts are divided Joint UK strategy defined

Our Strategy Start a UK Gamma Ray Association to co-ordinate activities e.g. multi-instrument campaigns, development Exploit VERITAS – similar performance to H.E.S.S. but different, Northern sky targets – total cost ~ £100k - £200k p.a. Minimal capital investment. Jim Hinton at Leeds to become involved in H.E.S.S. Sizeable (~ £1M) capital contribution to H.E.S.S. II aiming at higher sensitivity at low energies. RAL joins VHE gamma ray effort, other groups also interested (e.g. Liverpool, Oxford). H.E.S.S. & H.E.S.S. II to be the experiment towards which UK gamma ray activities gravitate. Post-2010 – plan UK contribution to the next major VHE gamma-ray facility (ESFRI?). Development work to start now.

H.E.S.S. II A single, 28m diameter dish Lowers threshold to ~ 20 GeV in standalone mode Improves overall array sensitivity in coincidence Key science questions: AGN population & the EBL; microquasar & XRB models; hadrons vs. leptons in SNR; pulsar detection; EGRET UiD sources; gamma ray bursts; dark matter.

After H.E.S.S. II? Crab 10% Crab 1% Crab GLAST MAGIC H.E.S.S. Current Simulations 20 wide-angle 10 m telescopes de la Calle Perez, Biller, astro-ph m stereo telescopes Konopelko Astropart.Phys. 24 (2005) 191

In summary… Exploitation of VERITAS H.E.S.S. II Build Exploitation of H.E.S.S. I & II Array development & design Array build

Why North and South? Understanding both AGN & SNR requires population studies Specific objects in both hemispheres require investigation (e.g. Cas A, Tycho, Galactic Centre, LMC/SMC…) Full sky coverage is desirable for multiwavelength multi-target campaigns

Technical Expertise of UK groups CCLRC/RAL: large scale project management/delivery; instrumentation (esp. single photon detection, fast electronics, communications); detector assembly (design/validation, test assemblies); data analysis & physics (data management, ‘gridification’) Durham University: mirror design/manufacture, atmospheric monitoring, calibration, simulations. Leeds University: fast signal transmission; advanced trigger systems; photodetectors; simulations.

The UK GRA Start with a general discussion between all members of involved and interested groups Form a small committee of (say) 2 members from each group Quarterly meetings to enable updating Regular reviews of strategy Eventually a more formal orghanisation with MoU etc.