Future directions in GroundBased GammaRay Astronomy Simon Swordy

Future directions in Ground-Based Gamma-Ray Astronomy Simon Swordy - Te. V 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 >20 ke. V Now still awaiting Nu. STAR NASA/Explorer Rocket/ x-rays<10 ke. V etc. .

WHY did <10 ke. V do so much better? The technology of x-ray mirrors as focusing optics could be used <10 ke. V, (now also possible >20 ke. V, hence Nu. STAR) Low energy x-ray detectors could be built from silicon -> CCDs Low energy single photon resolution became sub arcsec The energy window ~20 -100 ke. V is only being more fully explored recently because modern detector technology in SWIFT has angular resolution ~17 arcmin. (Coded mask and Cd. Zn. Te).

Ground-based gamma-ray astronomy will not be able get much better than ~5 arcmin (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 (Ge. V) ~100 <50 ~2000 <200 FOV (sq deg. ) ~12 ~100? ~5000 Livetime ~8% 10%? 95% >95% -ray ang. res. (deg. ) 0. 1 0. 05? 1 <0. 4 Collection Area (m 2) 105 106 104 105 -ray energy res. ~20% 15% ~75% 40% hadron rejection >99. 9% >99. 95% ~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. 80 m separation 4. 5. 6. 7. Telescope and Detector ø 10 m equivalent QE = 0. 25 (Bialkali) 15º field of view Facts and Figures 1. Outer radius: 640 m 2. Single cell area: 5543 m 2 3. Total area: 1. 06 km 2 Distance From Center Of Array [m]

Field of view [deg] Field of view [π sr] Observation Modes Collecting Area [km 2] Current IACTAs Narrow field of view <0. 01 km 2 @ 40 Ge. V 0. 05 -0. 1 km 2 @ 100 Ge. V 0. 2 -0. 3 km 2 @ 10 Te. V Square KM Array Continuum of modes Trade area for solid angle Parallel mode Narrow field of view 1 km 2 @ 40 Ge. V 2 km 2 @ 100 Ge. V 4 -5 km 2 @ 10 Te. V “Fly’s Eye” mode Wide field of view 0. 02 -0. 03 km 2 @ 40 Ge. V 0. 1 -0. 2 km 2 @ 100 Ge. V 3 -4 km 2 @ 10 Te. V

New Info… HAWC or mini. HAWC? (300 m versus 150 m 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 Fo. V increasing to 8 -10 degr. in outer sections Low-energy section ~10% area coverage 70 m 250 m Eth ~ 10 -20 Ge. V Eth ~ 50 -100 Ge. V Eth ~ 1 -2 Te. V 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 7 /√hr (wide angle) HE-ASTRO 23 /√hr (wide angle) 166 /√hr (sees Crab in 3 s!)

Ground Gamma-Ray Timeline Whipple, HEGRA, CANGAROOII, Milagrito HESS, MAGIC VERITAS, CANGAROOIII, Milagro HESS 2, MAGIC 2 VERITAS 2, CANGAROOIII+? , Mini. HAWC 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 ~105 m 2. Future ACT arrays head toward >1 km 2 • Higher altitude sites help ACTs and ground arrays, probably >3000 m (presently ~2000 m). • Coverage of full sky is highly desirable -> north and south facilities. • Given expected world-wide resources (<$500 M? ) 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