Second-timescale Glints from Satellites and Space Debris Detected with Tomo-e Gozen

A search for second-timescale optical transients is one of the frontiers of time-domain astronomy. However, it has been pointed out that reflections of sunlight from Earth-orbiting objects can also produce second-timescale ``glints. '' We conducted wide-field observations at 2 frames per second using Tomo-e Gozen on the 1. 05 m Kiso Schmidt telescope. We identified 1554 point-source glints that appeared in only one frame (0. 5 sec). Their brightness ranges from 11 to 16 mag, with fainter glints being more numerous. These glints are likely caused by satellites and space debris in high-altitude orbits such as the geosynchronous Earth orbit or highly elliptical orbits. Many glints brighter than 14 mag are associated with known satellites or debris with large apogees (> 30, 000 km). In contrast, most fainter glints are not associated with cataloged objects and may be due to debris with sizes of 0. 3--1 m. The event rate of second-timescale glints is estimated to be 4. 7 0. 2\ deg^{-2\ hr^-1} (average) and 9. 0 0. 3\ deg^{-2\ hr^-1} (near the equator) at 15. 5 mag. Our results demonstrate that high-altitude debris can represent a significant foreground in searches for second-timescale optical transients. They also imply that deep surveys such as Rubin/LSST will detect many of these glints in single-exposure images.