The Ultra-Fast Flash Observatory (UFFO) Burst Alert and Trigger Telescope (UBAT) has been designed and built for the localization of transient X-ray sources such as Gamma Ray Bursts (GRBs). As one of main instruments in the UFFO payload onboard the Lomonosov satellite (hereafter UFFO/Lomonosov), the UBAT's roles are to monitor the X-ray sky, to rapidly locate and track transient sources, and to trigger the slewing of a UV/optical telescope, namely Slewing Mirror Telescope (SMT). The SMT, a pioneering application of rapid slewing mirror technology has a line of sight parallel to the UBAT, allowing us to measure the early UV/optical GRB counterpart and study the extremely early moments of GRB evolution. To detect X-rays, the UBAT utilizes a 191.1 cm 2 scintillation detector composed of Yttrium Oxyorthosilicate (YSO) crystals, Multi-Anode Photomultiplier Tubes (MAPMTs), and associated electronics. To estimate a direction vector of a GRB source in its field of view, it employs the well-known coded aperture mask technique. All functions are written for implementation on a field programmable gate array to enable fast triggering and to run the device's imaging algorithms. The UFFO/Lomonosov satellite was launched on April 28, 2016, and is now collecting GRB observation data. In this study, we describe the UBAT's design, fabrication, integration, and performance as a GRB X-ray trigger and localization telescope, both on the ground and in space.

Publication date: 2017 Document VersionPublisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Gaikov, G., Jeong, . S., Agaradahalli, V. G., Park, I. H., Budtz-Jørgensen, C., Castro-Tirado, A. J., ... . Slewing mirror telescope of the UFFO-pathfinder: first report on performance in space. Optics Express, 25(23), 29143-29154. DOI: 10.1364/OE.25.029143 Slewing mirror telescope of the UFFO-pathfinder: first report on performance in space G. GAIKOV, 1,2 S. JEONG, 1,2,3,11 V. G. AGARADAHALLI, 1 Physics, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do, 16419, South Korea 2 Institute of Science and Technology in Space, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do, 16419 Technology and Science, Jawahar Nagar, Shamirpet Mandal, India * ilpark@skku.edu Abstract: To observe the early optical emissions from gamma ray bursts (GRBs), we built the Slew Mirror Telescope. It utilizes a 150 mm motorized mirror to redirect incoming photons from astrophysical objects within seconds and to track them as compensating satellite movements. The SMT is a major component of the UFFO-pathfinder payload, which was launched on April 28, 2016, onboard the Lomonosov satellite. For the first time, the slewing mirror system has been proven for the precision tracking of astrophysical objects during space operation. We confirmed that the SMT has 1.4 seconds of response time to the X-gamma-ray trigger, and is able to compensate for satellite drift and to track astrophysical objects with magnitudes from 7 to 18.

The payload of the UFFO (Ultra-Fast Flash Observatory)-pathfinder now onboard the Lomonosov spacecraft (hereafter UFFO/Lomonosov) is a dedicated instrument for the observation of GRBs. Its primary aim is to capture the rise phase of the optical light curve, one of the least known aspects of GRBs. Fast response measurements of the optical emission of GRB will be made by a Slewing Mirror Telescope (SMT), a key instrument of the payload, which will open a new frontier in transient studies by probing the early optical rise of GRBs with a response time in seconds for the first time. The SMT employs a rapidly slewingThe Lomonosov Mission Edited

We developed an X-ray detector using 36 arrays, each consisting of a 64-pixellated yttrium oxyorthosilicate (YSO) scintillation crystal and a 64-channel multi-anode photomultiplier tube. The X-ray detector was designed to detect X-rays with energies lower than 10 keV, primarily with the aim of localizing gamma-ray bursts (GRBs). YSO crystals have no intrinsic background, which is advantageous for increasing low-energy sensitivity. The fabricated detector was integrated into UBAT, the payload of the Ultra-Fast Flash Observatory (UFFO)/Lomonosov for GRB observation. The UFFO was successfully operated in space in a low-Earth orbit. In this paper, we present the responses of the X-ray detector of the UBAT engineering model identical to the flight model, using 241Am and 55Fe radioactive sources and an Amptek X-ray tube. We found that the X-ray detector can measure energies lower than 5 keV. As such, we expect YSO crystals to be good candidates for the X-ray detector materials for future GRB missions.

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