Orbital Foregrounds for Ultra-short Duration Transients

Abstract

Reflections from objects in Earth orbit can produce subsecond, star-like optical flashes similar to astrophysical transients. Reflections have historically caused false alarms for transient surveys, but the population has not been systematically studied. We report event rates for these orbital flashes using the Evryscope Fast Transient Engine, a low-latency transient detection pipeline for the Evryscopes. We select single-epoch detections likely caused by Earth satellites and model the event rate as a function of both magnitude and sky position. We measure a rate of -+ 1800 280 600 sky −1 hr −1 , peaking at m g =13.0, for flashes morphologically degenerate with real astrophysical signals in surveys like the Evryscopes. Of these, -+ 340 85 150 sky −1 hr −1 are bright enough to be visible to the naked eye in typical suburban skies with a visual limiting magnitude of V≈4. These measurements place the event rate of orbital flashes orders of magnitude higher than the combined rate of public alerts from all active all-sky fasttimescale transient searches, including neutrino, gravitational-wave, gamma-ray, and radio observatories. Shorttimescale orbital flashes form a dominating foreground for untriggered searches for fast transients in lowresolution, wide-angle surveys. However, events like fast radio bursts with arcminute-scale localization have a low probability (∼10 −5 ) of coincidence with an orbital flash, allowing optical surveys to place constraints on their potential optical counterparts in single images. Upcoming satellite internet constellations, like SpaceX Starlink, are unlikely to contribute significantly to the population of orbital flashes in normal operations.

High cadence optical transient searches using drift scan imaging II: Event rate upper limits on optical transients of duration <21 ms and magnitude <6.6

“…In this image, the peak brightness of the flash from the satellite corresponds to a magnitude of V ∼ 5. Corbett et al (2020) characterise the occurrence of flashes from satellites and measure a peak rate of 1 800± 600 280 per h per sky near the equator, at a peak magnitude of 6.8, assuming a flash duration of 0.4 s. This duration is comparable to what we have observed in Figure 4. The subsequent processing steps described in Paper I, determining the astrometry and photometry, need only be performed for any astronomical candidates subsequently confirmed to be high confidence candidates, after a detailed examination of the potential match.…”

Rotation periods of TESS Objects of Interest from the Magellan-TESS Survey with multiband photometry from Evryscope and TESS

“…Evryscope light curves of dim stars (g =15) reach comparable precision to TESS, attaining 10% photometric precision (Ratzloff et al 2019). In between light curve database updates, we may query light curves of individual sources not in the standard database at high computational cost using a separate Evryscope pipeline, Evryscope Fast Transient Engine (EFTE; Corbett et al 2020). The photometric performance and stability of the EFTE light curves is comparable to light curves from the standard pipeline.…”

“…The photometric performance and stability of the EFTE light curves is comparable to light curves from the standard pipeline. More details on the EFTE pipeline are found in Corbett et al (2020). We use light curves from both the standard and EFTE pipelines, which are tracked in the machinereadable version of Table 1.…”

High Cadence Optical Transient Searches using Drift Scan Imaging II: Event Rate Upper Limits on Optical Transients of Duration <21 ms and Magnitude <6.6

“…In this image, the peak brightness of the flash from the satellite corresponds to a magnitude of V∼5. Corbett et al (2020) characterise the occurrence of flashes from satellites and measure a peak rate of 1800± 600 280 per hour per sky near the equator, at a peak magnitude of 6.8, assuming a flash duration of 0.4 seconds. This duration is comparable to what we have observed in Figure 4.…”