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Wide Angle Very Low Threshold Air Cherenkov Imaging Telescope

Discovering VHE gamma ray sources using a wide angle telescope without the need for satellites or other detectors. A solution based on a Fresnel lens and prime-focus configuration is presented.

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Wide Angle Very Low Threshold Air Cherenkov Imaging Telescope

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  1. Quo Vadis ? Wide Field Imaging Razmick Mirzoyan MPI Munich, Germany A Wide Angle Very Low Threshold Air Cherenkov Imaging Telescope

  2. 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! Razmick Mirzoyan: Wide-Angle Telescope

  3. 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 ? Razmick Mirzoyan: Wide-Angle Telescope

  4. 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). Razmick Mirzoyan: Wide-Angle Telescope

  5. 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! Razmick Mirzoyan: Wide-Angle Telescope

  6. Recent wide angle tendencies inoptical astronomy • Megacam: a wide-field imaging camera 1° x 1° being designed for the prime focus of the 3.6m Canada-France-Hawaii 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 Razmick Mirzoyan: Wide-Angle Telescope

  7. 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. Razmick Mirzoyan: Wide-Angle Telescope

  8. 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 givenF/Dand given focal plane detector acceptanceq° (half angle)the relative shadowing effect in % is: 4 * (q/57.3)² * (F/D)² * 100 Razmick Mirzoyan: Wide-Angle Telescope

  9. 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. Razmick Mirzoyan: Wide-Angle Telescope

  10. Wide FoV based on prime-focustelescope 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 Razmick Mirzoyan: Wide-Angle Telescope

  11. Schmidt telescope allows one wide-angle imaging Razmick Mirzoyan: Wide-Angle Telescope

  12. Schmidt telescope ‚keeps‘ the spherical aberration low Razmick Mirzoyan: Wide-Angle Telescope

  13. VST: VLT Survey Telescope A 2.5 m telescope dedicated to Wide Field Imaging OWL, 100m diameter optical telescope project of ESO Razmick Mirzoyan: Wide-Angle Telescope

  14. Let us add a correction plate at the radius of curvature Razmick Mirzoyan: Wide-Angle Telescope

  15. 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. Razmick Mirzoyan: Wide-Angle Telescope

  16. A wide-angle camera 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 12 deg. 10 deg. Razmick Mirzoyan: Wide-Angle Telescope

  17. 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-of-view 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. Razmick Mirzoyan: Wide-Angle Telescope

  18. 1st 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 Razmick Mirzoyan: Wide-Angle Telescope

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