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Sebastian Achim Mueller

Publications and source records attributed to Sebastian Achim Mueller.

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Simulating an imaging atmospheric radio telescope to observe cosmic gamma rays and cosmic neutrinos

Observations of cosmic gamma~rays with energies above the 10$^{12}$ electronvolts (TeV) regime are often a direct probe of events where our theoretical predictions are challenged by extreme conditions. Because high energetic cosmic gamma-rays are rare, one needs collection areas with the size of soccer fields (10$^{5}$ m$^2$) or more to gather significant counting statistics in short time. The imaging atmospheric Cherenkov telescope detects cosmic gamma-rays in such large areas and currently offers the best reconstruction power for the cosmic particle's type, energy, and direction in particular. However, with only about 1,000 hours of dark and clear nights every year, the imaging atmospheric Cherenkov~telescope only has a duty cycle of about $12\%$. To overcome this limitation, we propose a novel imaging atmospheric radio telescope. By observing radio emission in the $10$ GHz regime from air showers, the imaging atmospheric radio telescope could observe 24/7, independent of the day night cycle, and almost independent of the weather. The novelty here is the high resolution imaging of the air shower's radio emission which might result in high resolution images as one finds them in imaging atmospheric Cherenkov~telescopes. We present a technique to simulate the image formation in the radio telescope using wave mechanics instead of conventional ray tracing. The imaging atmospheric radio telescope could increase our access more than eight-fold to an accurately reconstructed high energy gamma-ray-sky. Further, the imaging atmospheric radio telescope might also eight fold the observation power for cosmic neutrinos in the so called Earth-skimming technique.

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Imaging the radio-wave emission from extensive air showers

We propose a new way to observe cosmic-ray-induced air showers by imaging the radio emission. With simulations we demonstrate key features for imaging the radio-wave emission from air showers, which show similarities to the well-established atmospheric imaging Cherenkov technique in gamma-ray astronomy. In addition, we find that imaging the emission with a camera, consisting of multiple antennas, resolves emission that is not accessible to a single antenna. Pursuing this technique, with a camera operating in the GHz frequency domain, might be beneficial ultra-high-energy gamma-ray astronomy and other studies that include detailed observations of air showers.

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Exploring one giga electronvolt cosmic gamma rays with a Cherenkov plenoscope capable of recording atmospheric light fields, Part 1: Optics

Detecting cosmic gamma rays at high rates is the key to time-resolve the acceleration of particles within some of the most powerful events in the universe. Time-resolving the emission of gamma rays from merging celestial bodies, apparently random bursts of gamma rays, recurring novas in binary systems, flaring jets from active galactic nuclei, clocking pulsars, and many more became a critical contribution to astronomy. For good timing on account of high rates, we would ideally collect the naturally more abundant, low energetic gamma rays in the domain of one giga electronvolt in large areas. Satellites detect low energetic gamma rays but only in small collecting areas. Cherenkov telescopes have large collecting areas but can only detect the rare, high energetic gamma rays. To detect gamma rays with lower energies, Cherenkov-telescopes need to increase in precision and size. But when we push the concept of the -- far/tele -- seeing Cherenkov telescope accordingly, the telescope's physical limits show more clearly. The narrower depth-of-field of larger mirrors, the aberrations of mirrors, and the deformations of mirrors and mechanics all blur the telescope's image. To overcome these limits, we propose to record the -- full/plenum -- Cherenkov-light field of an atmospheric shower, i.e. recording the directions and impacts of each individual Cherenkov photon simultaneously, with a novel class of instrument. This novel Cherenkov plenoscope can turn a narrow depth-of-field into the perception of depth, can compensate aberrations, and can tolerate deformations. We design a Cherenkov plenoscope to explore timing by detecting low energetic gamma rays in large areas.

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Cherenkov-Plenoscope

Telescopes -- far seeing -- have since centuries revealed insights to objects at cosmic distances. Adopted for gamma-ray-astronomy, ground based Cherenkov-telescopes image the faint Cherenkov-light of air-showers induced by cosmic gamma-rays rushing into earth's atmosphere. In the race for the lowest possible energy-threshold for cosmic gamma-rays, these Cherenkov-telescopes have become bigger, and now reached their physical limits. The required structural rigidity for image-quality constrains a cost-effective construction of telescopes with apertures beyond 30 meter in diameter. Moreover, as the aperture increases, the narrower depth-of-field irrecoverably blurs the images what prevents the reconstruction of the cosmic particle's properties. To overcome these limits, we propose plenoptic-perception with light-fields. Our proposed 71 meter Cherenkov-plenoscope requires much less structural rigidity and turns a narrow depth-of-field into three-dimensional reconstruction-power. With an energy-threshold for gamma-rays of one Giga electron Volt, 20 times lower than what is foreseen for the future planned Cherenkov-Telescope-Array (CTA), the Cherenkov-plenoscope could become the portal to enter the sub second time-scale of the highly variable gamma-ray-sky. Also, this doctoral-thesis contains a second part on the prospects of single-photon-perception in Cherenkov-astronomy.

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Towards Robotic Operation with the First G-APD Cherenkov Telescope

The First G-APD Cherenkov Telecope is an Imaging Air Cherenkov Tele- scope operating since 2011 at the Observatorio del Roque de los Muchachos. One of the major goals of the FACT collaboration is to achieve robotic operation of the telescope. Since 2011 FACT is operated remotely. To reduce the necessity of human interven- tion, several programs were developed, most notably the shifthelper together with the pycustos library. This software monitors the telescope system and environmental conditions and calls the shifters in case human intervention is required. This will lead to FACT being the first IACT with all shifters asleep during regular observations. The software presented here is open source and under MIT License.

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