Capability of Cherenkov Telescopes to Observe Ultra-fast Optical Flares

TL;DR

This study demonstrates the capability of Cherenkov telescopes with microsecond resolution to detect ultra-fast optical flares, revealing potential for observing rapid astrophysical phenomena near compact objects.

Contribution

It introduces a novel observational setup using a Cherenkov telescope with a dedicated photometer to detect microsecond-scale optical transients from astrophysical sources.

Findings

Detected background-free optical events between 3 and 500 microseconds.

Identified flashes from space debris demonstrating setup sensitivity.

Showed potential to observe rapid flares from stellar-mass black holes and neutron stars.

Abstract

The large optical reflector (~ 100 m^2) of a H.E.S.S. Cherenkov telescope was used to search for very fast optical transients of astrophysical origin. 43 hours of observations targeting stellar-mass black holes and neutron stars were obtained using a dedicated photometer with microsecond time resolution. The photometer consists of seven photomultiplier tube pixels: a central one to monitor the target and a surrounding ring of six pixels to veto background events. The light curves of all pixels were recorded continuously and were searched offline with a matched-filtering technique for flares with a duration of 2 us to 100 ms. As expected, many unresolved (<3 us) and many long (>500 us) background events originating in the earth's atmosphere were detected. In the time range 3 to 500 us the measurement is essentially background-free, with only eight events detected in 43 h; five from lightning and three presumably from a piece of space debris. The detection of flashes of brightness ~ 0.1 Jy and only 20 us duration from the space debris shows the potential of this setup to find rare optical flares on timescales of tens of microseconds. This timescale corresponds to the light crossing time of stellar-mass black holes and neutron stars.