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| Author(s): |
Jessica Dipold
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT) |
| Defense date: | 2015-02-10 |
| Examining board members: |
Luiz Vitor de Souza Filho;
Valter Luiz Líbero;
Marcelo Augusto Leigui de Oliveira
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| Advisor: | Luiz Vitor de Souza Filho |
| Abstract | |
γrays are billions of times more energetic than visible photons. Through the sky observation of this kind of radiation, it is possible to study phenomena like the emission from pulsars, supernova explosions and black holes, as well as gamma-ray bursts, one of the greatest mysteries in modern astrophysics. The main technique used in astrophysical observations in γrays showers is the Imaging Cherenkov Telescope, which can image the trajectory of gamma-rays during its passage through the atmosphere by observing its emission of Cherenkov radiation. There are several successful experiments currently functioning, such as VERITAS, MAGIC and HESS. In 2006, a new observatory was proposed, which will have a sensitivity one order of magnitude better than any of the existing experiments. The Cherenkov Telescope Array (CTA) is in its prototype phase, and will consist of several tens of Cherenkov telescopes with different sizes, which will allow observation in many different regions of the γray spectrum. The site where the Observatory will be constructed is not yet decided and it depends on several geographic characteristics, being one of the most important the observable time, which must be above 80% to be considered as a possible site. One of the proposed sites is located in the north of Argentina, close to the city of San Antonio de los Cobres (SAC). In order to demonstrate the functionality of the site, we developed a facility on it to test the optical and mechanical properties of four prototype mirrors, as well as their condensation conditions. Three Glass/Aluminum hexagonal mirrors, 1.5 meters flat-to-flat diameter, and one Glass/Dielectric circular mirror, 0.5 meters diameter, all spherical with a focal position between 15 and 16 meters, were exposed to the environmental conditions of SAC from May/2013 until June/2014. To test their mechanical and optical properties variation because of the environment exposition, two different tests were made. In order to verify if the curvature and smoothness of the mirrors remained constant, we developed an equipment at the Instituto the Física de São Carlos that could measure the 2f position, where the image formed by the mirror is the smallest as possible, and its Point Spread Function (PSF), the size of the image made by the mirror by a punctual source. The focal position of all mirrors was proven to be stable, while the PSF size showed small differences according to the exposure time. To examine the variation of the Aluminum (or Dielectric) covering of the mirrors we measured its reflectivity variation through a portable spectrometer fabricated by OceanOptics, which showed that the dielectric covering is more stable than the Aluminum ones, even though all of them showed a constant reflectivity in the 300-400 nm range. And finally, to test both the mirror and the site quality in observation time, we calculated the condensed time of two mirrors during the period of December/2013 until April/2014. This was done through automatic pictures of each mirror taken remotely during the night, providing data to observe daily changes in the quality of the mirror surfaces as well as if there is condensation during that period. A Glass/Aluminum mirror and the Glass/Dielectric one were tested, both showing very similar results of around 20% condensed time, being in the limit of the 80% of observational time forementioned. Through these tests, we intend to provide a technique for the calculation of condensed time in any proposed site. (AU) | |
| FAPESP's process: | 12/23676-7 - Mirror characterization for use in Cherenkov telescopes |
| Grantee: | Jessica Dipold |
| Support Opportunities: | Scholarships in Brazil - Master |