Download Quo Vadis

Quo Vadis ?
Wide Field Imaging
Razmick Mirzoyan
MPI Munich, Germany
A Wide Angle Very Low Threshold
Air Cherenkov Imaging Telescope
22 February 2006
• How can one find, independent on satellites
and/or any other space or ground-based
detectors, operating at different wavelengths,
many VHE gamma ray sources ?
• A sensitive sky survay instrument can do it!
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Stationary wide field of
view instruments
• Air shower arrays like Tibet and ARGO-YBJ or
MILAGRO like instruments measure particles
from air showers and cannot go much below 1 TeV.
They provide relatively low sensitivity.
• Imaging air Cherenkov telescope technique has
proven to be a very sensitive one. Few tens of
sources are discovered in recent years.
• Can one build a stationary wide angle Cherenkov
telescope ? A solution based on Fresnel lens ?
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
A Fresnel lens has low losses for incident angles of light of up
to 10°-15°. For an incident angle of light of 25° the loss can be
~ 30 % (see below the data from EUSO experiment).
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Wide angle telescope ?
• Can one build a relatively wide-angle
tracking telescope ?
• In recent two years HESS has shown that
even with ~ 4° diameter camera/s they
could find quite an impressive number of
new sources!
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Recent wide angle tendencies in
optical astronomy
• Megacam: a wide-field imaging camera 1° x 1° being
designed for the prime focus of the 3.6m Canada-FranceHawaii Telescope. Includes 40 thinned CCDs.
• VISTA is the Visible and Infrared Telescope
for Astronomy, a new 4m wide field survey
telescope under development which
will be the world-leading facility for and IR (and
potentially for optical) survey work. Initially 1° x 1°, later
on 1.5° x 1.5° FoV.
• VST: A 2.5 m VLT Survay Telescope. 1° x 1° FoV
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Some relevant data for wide FoV
• The hemisphere subtends 20626 deg.². If one will limit the
zenith angle to 60°, one can observe half of the
hemisphere, i.e. about 10000 deg.²
• Imagine a camera measuring in 10° x 10° FoV, i.e.
subtending 100 deg.² in the sky. One can make 100
exposures with such a camera to cover the entire sky.
• A good observatory will provide ~ 1000 h observation time
in one year. One can make 100 observations, each of 10 h
duration.
• A good telescope system can find a g source of ~ 1 % Crab
in 10 h.  All-sky survay in 1 year with 1 % Crab
sensitivity.
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
A prime-focus solution
One of the main problems is the shadowing of the main
mirror by the camera. For any telescope the focal plane
scale in units of cm/degree is:
F * (1/57.3) cm/deg.
For MAGIC it makes: 1700 cm x (1/57.3) = 30 cm/deg.
For a telescope of simple configuration (single reflector +
camera) with given F/D and given focal plane detector
acceptance q (half angle) the relative shadowing effect in
% is:
4 * (q/57.3)² * (F/D)² * 100
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
A prime-focus solution
An imaginary MAGIC-size telescope with a 30 deg. (half)
acceptance (i.e. full angle of 60 deg.) will have a shadowing
of 100 % (the camera diameter will be ~18m and the entire
reflector will be in shadow).
If one will limit the camera size, for example, to 12° (full
size) (or to +6° and –6°) then the camera diameter will be
about 4m and it will shadow only ~5 % of the reflector
area.
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Wide FoV based on prime-focus
telescope solutions
Schliesser & Mirzoyan, Astrop. Phys., 2005
As one can see from
the calculations on
the left, it is do
possible to
construct a 10° FoV
telescope.
The drawback: one
will need to provide:
F/D ≥ 2.7 optics
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Schmidt telescope allows one
wide-angle imaging
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Schmidt telescope ‚keeps‘ the
spherical aberration low
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
VST: VLT Survey Telescope
A 2.5 m telescope dedicated to
Wide Field Imaging
OWL, 100m diameter optical telescope
project of ESO
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Let us add a correction plate at
the radius of curvature
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Other than shadowing limitation on the maximum
size of the field of view
• Providing a large field-of-view, because of the zenith
angle dependence, the showers of different E will
reach their maxima on different distances from the
telescope.
• This means that their images will be smeared out
depending on their angular deviation from the
telescope‘s axis and the best focus plane of the
telescope. Needs to be studied what is the upper limit
of the maximum field-of-view.
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
A wide-angle camera
12 deg.
A 12° x 12° camera will have an active
area of 10° x 10° (=100 deg.²) (because of
the edge effects the 1° rim will not be in
the trigger and could be used for
measuring shower tails).
One can imagine a 11°x11° high
resolution part with 12100 pixels of 0.10°
size and the 0.5 ° edges covered by pixels
of ~0.2° size, in total ~700 pixels.
Total number used PMTs = 12800 or
equivalent number of SiPM
10 deg.
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
Wide-Angle Telescopes
(Cherenkov) (WATCH)
• We have carried out detailed ray tracings that
show that it is do possible to design a telescope
configuration which can provide a full field-ofview of 10° - 20°, everywhere providing 1´
optical resolution.
• A fast-optics solution can provide a relatively
compact sizes for the telescope. For example, a
F/0.7 optics will provide a ‚length‘ of 1.4 x D.
• We have simulated a D=28m telescope that can
provide a useful D=22m.
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope
st
1
Cost Estimate
• One needs to find a readout that costs
< 500.-€/channel. That will cost 12800 x 0.5.-k€ =
6,4.-M€
• The light-sensors may cost: 2.-M€
• The frame may cost 5.-M€ (including secondary
optics)
• The mirrors may cost 1,5.-M€
• Total: ~ 15.-M€ / telescope
• A system of 10 such telescopes may become an
extremely powerful next generation g instrument
22 February 2006
Razmick Mirzoyan: Wide-Angle
Telescope