Mgr. Jan Ebr, Ph.D.
Both cosmic-ray and gamma experiments, in which our department participates, include optical telescopes which need precise real-time data on atmospheric transparency. Modern photosensors (which we study in the respective laboratory) enable efficient atmospheric monitoring using stellar photometry. We are currently operating five small robotic telescopes known as FRAMs – two at the Pierre Auger Observatory and three at the future Cherenkov Telescope Array Observatory (CTAO) sites, with several more FRAMs in preparation. We also develop the application of infrared Lidars for CTAO for cloud height measurements and we collaborate with the Astronomical Institute on the operation of Sun/Moon Photometers at CTAO sites for aerosol studies.
FRAMs can not only quickly provide transparency information for any location in the sky as required by the astroparticle experiments, but we also have shown that the they can precisely measure the overall vertical aerosol optical depth (VAOD) at a precision comparable with the standard Lidars, but without the undesirable production of stray light. We work towards extending this method to measurements of wavelength dependence of the optical depth and thus of the physical properties of the aerosols. In their spare time, the FRAMs conduct astronomical observations, which have contributed to over 40 publications so far, the discovery of ~500 variable stars and hundreds of astronomical circulars; recently one of the FRAMs was used in the first comet discovery by a Czech astronomer in over two decades – C/2024 Y1 (Mašek). Quick follow-up observations of gamma-ray bursts, including some of the most peculiar GRBs ever detected, contribute to multi-messenger studies of sources detected by the large astroparticle experiments.
The first FRAM was installed at the Pierre Auger Observatory already in 2005 and is being continuously upgraded. The second Auger FRAM was installed in 2021 and we are currently developing a further variation on the concept, known as framNG, which will replace the aging infra-red cameras for real-time cloud coverage monitoring across the entire field of view of the fluorescence telescopes of the Observatory. Between 2017-2019, three more FRAMs were installed at the future Cherenkov Telescope Array Observatory sites, where they carry out long-term measurements of the aerosol conditions and serve as pathfinders for the installation of further CTAO instrumentation. These FRAMs will eventually become a key link in the operations of the Observatory, informing the immediate operators' reaction to the atmospheric conditions. They will be a part of a rich atmospheric monitoring program designed to maximize the scientific output of CTAO: in this program, we are also developing the steerable ceilometers (infra-red Lidars) and had been, for many years, for the Sun/Moon Photometers (now led by the Astronomical Institute); additionally, FZU colleagues from the Joint Laboratory of Optics in Olomouc built and operate All-sky Cameras.