future directions in ground-based gamma-ray astronomy
DESCRIPTION
Future directions in Ground-Based Gamma-Ray Astronomy. Simon Swordy - TeV Particle Astro II, UW Madison, 2006. Discuss. Future of ground-based gamma-rays, postulate: "Where there's a will there's a way..". Will. Way. Some History. The Crab in early x-rays from a rocket flight. Also. - PowerPoint PPT PresentationTRANSCRIPT
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?
Balloon/ x-rays >20keV
Then Now
still awaiting NuSTARNASA/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 recentlybecause modern detector technology in SWIFT has angularresolution ~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 morphologyof 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 resolutionIncrease live-time for air cherenkov
Dis
tan
ce F
rom
Cen
ter
Of
Arr
ay [
m]
Distance From Center Of Array [m]
Array1. 217 telescopes 2. 8 hexagonal rings + 13. 80m separation
Telescope and Detector1. ø10m equivalent2. QE = 0.25 (Bialkali)3. 15º field of view
Facts and Figures1. Outer radius: 640m2. Single cell area: 5543m2 3. Total area: 1.06km2
Some examples:S. Fegan, V. Vassiliev, UCLA "HE-ASTRO" concept
Fie
ld o
f vi
ew [
π s
r] Field
of view
[deg
]
Current IACTAsNarrow field of view<0.01 km2 @ 40 GeV0.05-0.1 km2 @ 100 GeV0.2-0.3 km2 @ 10 TeVSquare KM ArrayContinuum of modesTrade area for solid angleParallel modeNarrow field of view1 km2 @ 40 GeV2 km2 @ 100 GeV4-5 km2 @ 10 TeV
“Fly’s Eye” modeWide field of view0.02-0.03 km2 @ 40 GeV0.1-0.2 km2 @ 100 GeV3-4 km2 @ 10 TeV
Observation Modes
Collecting Area [km2]
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
HAWC or miniHAWC? (300m versus 150m baseline)
New Info…
Milagro group + collaborators
few 1000 m
High-energy section~0.05% area coverage
Eth ~ 1-2 TeV
250 m
Medium-energy section~1% area coverage
Eth ~ 50-100 GeV
70 m
Low-energy section~10% area coverage
Eth ~ 10-20 GeV
Hofmann: Array layout: 2-3 Zones
FoV increasingto 8-10 degr.
in outer sections
CTA - European Initiative (HESS+MAGIC)
Not to scale !
Option:Mix of telescope types
Sensitivity on Crab:
Whipple 5/√hrMilagro ~8/√yr (wide angle)
VERITAS-4, etc 23/√hr
HAWC 7/√hr (wide angle)
HE-ASTRO 23 /√hr (wide angle)HE-ASTRO 166 /√hr (sees Crab in 3s!)
Whipple, HEGRA, CANGAROOII,
Milagrito
HESS, MAGIC VERITAS, CANGAROOIII,
Milagro
HESS2, MAGIC2 VERITAS2, CANGAROOIII+?,
MiniHAWC
CTA, HE-ASTRO,HAWC, +….
Ground Gamma-Ray Timeline
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