1. Future directions in Ground-Based Gamma-Ray Astronomy Simon Swordy - TeV Particle Astro II, UW Madison, 2006

2. Future of ground-based gamma-rays, postulate: "Where there's a will there's a way.." Discuss..

4. Some History........

5. The Crab in early x-rays from a rocket flight....

6. Also....

7. Balloon "sky survey"......

8. Catalog of objects, mostly not there...

9. What happened next? Balloon/ x-rays >20keV Then Now still awaiting NuSTAR NASA/Explorer Rocket/ x-rays<10keV etc....

10. 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).

11. 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.....

12. So what "ways" are there and where might they go? Air CerenkovFutureParticle ArraysFuture Energy Thr (GeV) ~100<50~2000<200 FOV (sq deg.) ~12~100?~5000 Livetime~8%10%?95%>95%  -ray ang. res. (deg.) 0.10.05?1<0.4 Collection Area (m 2 ) 10 5 10 6 10 4 10 5  -ray energy res. ~20%15%~75%40% hadron rejection >99.9%>99.95%~90%

13. "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

14. Distance From Center Of Array [m] 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: 5543m 2 3.Total area: 1.06km 2 Some examples: S. Fegan, V. Vassiliev, UCLA "HE-ASTRO" concept

15. Field of view [π sr] Field of view [deg] Current IACTAs Narrow field of view <0.01 km 2 @ 40 GeV 0.05-0.1 km 2 @ 100 GeV 0.2-0.3 km 2 @ 10 TeV Square KM Array Continuum of modes Trade area for solid angle Parallel mode Narrow field of view 1 km 2 @ 40 GeV 2 km 2 @ 100 GeV 4-5 km 2 @ 10 TeV “Fly’s Eye” mode Wide field of view 0.02-0.03 km 2 @ 40 GeV 0.1-0.2 km 2 @ 100 GeV 3-4 km 2 @ 10 TeV Observation Modes Collecting Area [km 2 ]

16. HAWC or miniHAWC? (300m versus 150m baseline) New Info…

17. Milagro group + collaborators

18. few 1000 m High-energy section ~0.05% area coverage E th ~ 1-2 TeV 250 m Medium-energy section ~1% area coverage E th ~ 50-100 GeV 70 m Low-energy section ~10% area coverage E th ~ 10-20 GeV Hofmann: Array layout: 2-3 Zones FoV increasing to 8-10 degr. in outer sections CTA - European Initiative (HESS+MAGIC)

19. Not to scale ! Option: Mix of telescope types

20.  Sensitivity on Crab: Whipple 5  /√hr Milagro ~8  /√yr (wide angle) VERITAS-4, etc 23  /√hr HAWC 7  /√hr (wide angle) HE-ASTRO23  /√hr (wide angle) HE-ASTRO166  /√hr (sees Crab in 3s!)

21. Whipple, HEGRA, CANGAROOII, Milagrito HESS, MAGIC VERITAS, CANGAROOIII, Milagro HESS2, MAGIC2 VERITAS2, CANGAROOIII+?, MiniHAWC CTA, HE-ASTRO, HAWC, +…. Ground Gamma-Ray Timeline

22. 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 ~10 5 m 2. Future ACT arrays head toward >1km 2 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 ( 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