Transcript swordy_1

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…
QuickTi me™ and a
TIFF (Uncompressed) 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