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Future directions in Ground-Based Gamma-Ray Astronomy Simon Swordy - TeV Particle Astro II, UW Madison, 2006 Future of ground-based gamma-rays, postulate: "Where there's a will there's a way.." Discuss.. Some History........ The Crab in early x-rays from a rocket flight.... Also.... Balloon "sky survey"...... Catalog of objects, mostly not there... What happened next? Then Balloon/ x-rays >20keV Now still awaiting NuSTAR NASA/Explorer Rocket/ x-rays<10keV etc.... WHY did <10keV do so much better? The technology of x-ray mirrors as focusing optics could be used <10keV, (now also possible >20keV, hence NuSTAR) Low energy x-ray detectors could be built from silicon -> CCDs Low energy single photon resolution became sub arcsec The energy window ~20-100keV is only being more fully explored recently because modern detector technology in SWIFT has angular resolution ~17arcmin. (Coded mask and CdZnTe). Ground-based gamma-ray astronomy will not be able get much better than ~5arcmin (for single gamma), so several objects will always seem close to point-like (e.g. Cass A, Tycho, Crab..) It cannot compete with optical, radio, soft x-ray in the detailed morphology of sources..... but it can provide a clear outline of the extreme non-thermal pieces of our Galaxy and beyond. So..... So what "ways" are there and where might they go? Air Cerenkov Future Particle Arrays Future Energy Thr (GeV) ~100 <50 ~2000 <200 FOV (sq deg.) ~12 ~100? ~5000 ~5000 Livetime ~8% 10%? 95% >95% -ray ang. res. (deg.) 0.1 0.05? 1 <0.4 Collection Area (m2) 105 106 104 105 -ray energy res. ~20% 15% ~75% 40% hadron rejection >99.9% >99.95% ~90% ~90% "Easy" ways to go.. Make 'em bigger (increase to an array size of sqkm) Make 'em higher (go up a bigger mountain) "Tricky" ways to go... Lower energy threshold (going up a mountain helps, high QE devices help) Increase FOV for air cherenkov (some optical limits to this) Seemingly impossible stuff... Get better single photon angular resolution Increase live-time for air cherenkov Distance From Center Of Array [m] Some examples: S. Fegan, V. Vassiliev, UCLA "HE-ASTRO" concept Array 1. 217 telescopes 2. 8 hexagonal rings + 1 3. 80m separation Telescope and Detector 1. ø10m equivalent 2. QE = 0.25 (Bialkali) 3. 15º field of view Facts and Figures 1. Outer radius: 640m 2. Single cell area: 5543m2 3. Total area: 1.06km2 Distance From Center Of Array [m] Field of view [deg] Field of view [π sr] Observation Modes Collecting Area [km2] Current IACTAs Narrow field of view <0.01 km2 @ 40 GeV 0.05-0.1 km2 @ 100 GeV 0.2-0.3 km2 @ 10 TeV Square KM Array Continuum of modes Trade area for solid angle Parallel mode Narrow field of view 1 km2 @ 40 GeV 2 km2 @ 100 GeV 4-5 km2 @ 10 TeV “Fly’s Eye” mode Wide field of view 0.02-0.03 km2 @ 40 GeV 0.1-0.2 km2 @ 100 GeV 3-4 km2 @ 10 TeV New Info… QuickTime™ and a TIFF (U ncompressed) decompressor are needed to see this picture. HAWC or miniHAWC? (300m versus 150m baseline) Milagro group + collaborators CTA - European Initiative (HESS+MAGIC) Hofmann: Array layout: 2-3 Zones High-energy section ~0.05% area coverage Medium-energy section ~1% area coverage FoV increasing to 8-10 degr. in outer sections Low-energy section ~10% area coverage 70 m 250 m Eth ~ 10-20 GeV Eth ~ 50-100 GeV Eth ~ 1-2 TeV few 1000 m Option: Mix of telescope types Not to scale ! Sensitivity on Crab: Whipple Milagro 5/√hr ~8/√yr (wide angle) VERITAS-4, etc 23/√hr HAWC HE-ASTRO HE-ASTRO 7/√hr (wide angle) 23 /√hr (wide angle) 166 /√hr (sees Crab in 3s!) Ground Gamma-Ray Timeline Whipple, HEGRA, CANGAROOII, Milagrito HESS, MAGIC VERITAS, CANGAROOIII, Milagro HESS2, MAGIC2 VERITAS2, CANGAROOIII+?, MiniHAWC CTA, HE-ASTRO, HAWC, +…. Some Ways Forward: • In principle, collection area can be increased ad infinitum. The collection area of present ACTs is defined by the light pool size. The detector becomes larger than the light pool above ~105m2. Future ACT arrays head toward >1km2 • Higher altitude sites help ACTs and ground arrays, probably >3000m (presently ~2000m). • Coverage of full sky is highly desirable -> north and south facilities. • Given expected world-wide resources (<$500M?) this will probably be a limit -> two observatories • All-sky monitoring capability at <0.1 Crab level seems essential. Possibly with a co-located HAWC-type detector, or with a single HE-ASTRO-type detector, or maybe something new. • The interested science community will probably grow significantly - we need to get our world-wide act together