UBAT of UFFO/Lomonosov: The X-Ray Space Telescope to Observe Early Photons from Gamma-Ray Bursts

Abstract

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.

Detection of Low-Energy X-rays Using YSO Scintillation Crystal Arrays for GRB Experiments

“…After the launch, calibration of the satellite and payloads, including the UFFO/Lomonosov, was carried out for approximately seven months, but unfortunately, the operation was ended before any GRB data could be acquired because of a power supply failure in the satellite. UFFO/Lomonosov consists of two telescopes: a UFFO Burst Alert and Trigger telescope (UBAT) [25] and an SMT [26,27]. The UBAT is an X-ray trigger telescope, and the SMT is a UV/optical telescope, as shown in Figure 1.…”

“…UFFO/Lomonosov consists of two telescopes: a UFFO Burst Alert and Trigger telescope (UBAT) [25] and an SMT [26,27]. The UBAT is an X-ray trigger telescope, and the SMT is a UV/optical telescope, as shown in Figure 1.…”

Slewing mirror telescope of the UFFO-pathfinder: first report on performance in space

“…The instrument has a 17 × 17 FoV and a resolution of 4.2 over 256×256 pixels. The SMT is built to cover the half-coded FoV of UBAT [20], i.e. ±35°through the utilization of its slewing mirror.…”

“…Correction of the FoV is performed once per second. Figure 5 (bottom) shows the drift of the FoV over a one second interval (frames 1-15) and its compensation by the mirror system (frames [16][17][18][19][20]. Each succeeding 1-bit frame is shifted from the previous.…”

“…For the detection and localization of GRB events at X-ray wavelengths, the UFFO Burst Alert and Trigger Telescope (UBAT) is used [20,21]. The UBAT is a coded mask camera with 70°× 70°h alf coded FoV, able to localize bright GRBs within a 1 second integration time.…”