Download Technical Challenges and Parameters for a Future Design Simon Swordy University of Chicago

Technical Challenges and Parameters for
a Future Design
Simon Swordy
University of Chicago
gamma-ray future meeting, SLAC/KIPAC 11/8/2007
Now What?
Mehr Licht!
Mehr Bereich
Mehr Auflösung
Verringern Sie Energieschwelle
Goethe
Science Drivers
•
More Sensitivity (~10-13 vs. existing ~10-12 ergs/cm2 s @ 1TeV)
•
Lower Energy Threshold (~40GeV vs. existing ~100GeV at peak)
•
More Sky Coverage (π steradians vs. existing π/100 @ 1TeV)
•
More Detail (~1-2arcmin vs. existing ~5arcmin for a photon @ 1TeV)
More Sensitivity - make it bigger
80-120m
More Sensitivity - make it bigger
One "cell"
Array size larger
than Cerenkov
pool
(e.g. figure from
AGIS r+d prop.)
Sensitivity x10
HESS/VERITAS
@ 1TeV
but..............
50 Telescopes
Lower Energy Threshold
(Rate Peak on Crab-like Spectra)
"Cell-Effect" makes effective area at low-E relatively large for a big array,
compared to small array of 3 or 4 mid-diameter telescopes.
Simulations for Crab-like spectra, 7m telescopes w/separation
(Fegan and Vassiliev, ICRC 2007)
Energy Threshold variations w/Dimensions
• Ratio of mirror diameter
D and separation L
constant for a given
threshold energy.
• 40 GeV threshold with 8m
mirrors at 100m separation
(Fegan and Vassiliev ICRC 2007)
More sky coverage comes easily to an array……
Field of view [deg]
Field of view [π sr]
Collecting Area vs. Field Of View
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
Angular Resolution - Morphology
VERITAS
Single γ resolution
(arcmin)
~5
GLAST
~10
SWIFT
~17
Chandra
~0.01
Future Gamma
~1-2
Instrument
Image Resolution is Crucial for Galactic Science
Some kind of signal
It’s human!
High detail!
It’s not one
of these!
Limiting Angular Resolution for Cerenkov Instruments
(from W. Hofmann astro-ph/0603076)
1.5 arcminutes @ 1TeV could be reasonable?
=> 10 times the picture resolution of VERITAS
=> resolution ~half pixel size - i.e. 3 arcminute = 0.05 degree pixels
High Pixel Resolution is also Important for Low
Energy Gamma Discrimination
(Vassiliev and Fegan ICRC 2007 and previous Cerenkov workshops)
40GeV
VERITAS
100GeV
~40GeV Gamma
Red - gamma
Green - NSB
Some reflections on high resolution:
• High resolution images in the TeV regime are very
important for galactic sources.
• High resolution also has importance for image processing to
increase sensitivity at low energy (40GeV)- important for
extragalactic sources, where source morphology is not as
important.
Parameter Guesses……
• 50 8m diameter telescopes on 100m baselines
• Array size 700m x 700m, altitude ~2.5-3km
• 40GeV (peak counting) energy threshold
• 3-4 arcminute pixels (0.05-0.07deg)
Technical Challenges……
• For something of this size, reliability and overall
systems engineering during development are far more
important. We cannot have 20% (10!) telescopes
needing something fixing all the time.
• Electronics and detector cost per pixel must be low to
provide high resolution cameras.
Ferrari P4 $4M
(no reliability data)
Toyota Camry $15k
(Autoworld - most reliable car 2006)
•The only high image resolution detectors that are realistic from a cost
standpoint (MAPMTs, SiAPDs) have pixel sizes ~10mm-3mm. We
need an optical design with a small plate scale, i.e. ~1arcminute/mm
(see later talks)
• The trigger system will be very challenging. It does not need to act on
the high resolution pixel angular scale (0.05 deg) but on ~0.15 deg
scale (see later talks).
Fiscal Challenges:
• The overall scale of this project is ~$100M
• Following conventional wisdom, the optimum distribution is somewhere
close to telescope+mirrors cost = electronics+detector cost. Each telescope
costs $1M, each camera + electronics cost $1M.
• A reflector of effective diameter 7 degrees needs 10,000 pixels of 0.06
degrees. This means $100 per pixel -> maybe possible because of scaling
savings, but definitely a new regime (VERITAS costs ~$1,500 per pixel)
which will require a new paradigm for the engineering approach.
• Non-spherical mirror manufacture will most likely be required. Exploration of
cost effective replication schemes is needed.
• High quantum efficiency devices are very attractive. Doubling existing bialkali QE to ~50% would reduce the cost of the telescope by a significant
amount (x2-3) and might ultimately be a “tipping point” for a project like this.
Site Challenges:
Altitude:
( from EOS/NASA)
• There is no time like the present for exploring possible sites
Clouds…
(EOS/NASA/MOSDIS)
Lightning
(from EOS/NASA)
Community Challenge:
• For an instrument of this size we need a large (several hundred
scientist) core community and plenty of other interested
astronomers.
• This will have to be more like a facility instrument than existing
telescope arrays (VERITAS/HESS/MAGIC/CANGAROO).
• It will need on site ~20 technical/management people to keep it
running.
• We will need to capitalize on the community which will be created
by GLAST to make this happen.
Rumsfeldian Analysis
Known knowns:
• the field of TeV gamma-rays is transforming to “mainstream”
• we need ~$100M to take the next x10 step
• in the US we must be high in the next decadel survey “medium” class
• we cannot hit this budget level with existing technology
• technically reliable, cost effective design is vital
Known unknowns:
• how many more sources will we see at x10 sensitivity?
• will high QE devices become a real option?
• will highly pixellated devices become real?
• where will it (they) be sited?
Unknown unknowns:
• make the best honest scientific case, attempts at tailoring to current
agency perspectives can backfire..
• something really interesting is discovered with the present
instruments…..
Summary..
Go up a mountain
Build a bunch of telescopes
Take some data
BINGO!
sorted