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

TL;DR

This work investigates second-timescale optical glints caused by reflections from satellites and space debris using the Tomo-e Gozen instrument. A GPU-accelerated SSD-based pipeline detects 0.5 s point-source glints from wide-field video data, yielding 1554 candidates, of which 1088 repeat detections are broadly consistent with high-altitude GEO/HEO debris and 466 are single detections. Bright glints correlate with catalogued objects, while a substantial faint population (0.3–1 m) remains largely uncatalogued, suggesting many small, high area-to-mass ratio debris. The estimated areal event rates are $R \approx 4.7 \pm 0.2$ and $9.0 \pm 0.4$ deg$^{-2}$ hr$^{-1}$, respectively, highlighting that GEO/HEO debris constitute a significant foreground for second-timescale transients and that deep surveys like Rubin/LSST will frequently detect such glints in single exposures. These findings motivate mitigation strategies and careful survey design to separate astrophysical second-timescale transients from satellite/debris foregrounds.

Abstract

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 $4.7 \pm 0.2\ {\rm deg^{-2}\ hr^{-1}}$ (average) and $9.0 \pm 0.3\ {\rm deg^{-2}\ hr^{-1}}$ (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.

Figures (11)

• Figure 1: (Top) Survey footprints of our observations in the equatorial coordinate. The color represents the total exposure time for each part of the sky. (Bottom) Distribution of the detected glints. The blue points show all the glints while the orange points show those associated with catalogued objects. Note that the coordinates of the glints are given as viewed from the Kiso observatory.
• Figure 2: Cumulative areal exposure (${\rm deg^2 \ hr}$) of our survey as a function of $5 \sigma$ limiting magnitude.
• Figure 3:
• Figure 4: Example of detected glints. For the glints matched with catalogued objects, their common names are also given. Each image section has a size of 100 pixels $\times$ 100 pixels (about 2 arcmin $\times$ 2 arcmin). North is up and East is left. Note that some faint sources (i.e., those in SIRIUS 3 (first row), uncatalogued source (fourth row), and HIMAWARI 5 AKM (fifth row)) are not detected with SSD, and these are not included in the number of detection.
• Figure 5: Distribution of solar separation angles for the detected glints (blue). For comparison, the gray line shows the (normalized) angle distribution for our survey footprints. The thin dashed line shows the uniform distribution.