# Proving the outstanding capabilities of IACTs in high time resolution optical astronomy

## TL;DR

This paper demonstrates the exceptional high time resolution capabilities of Imaging Atmospheric Cherenkov Telescopes (IACTs) in optical astronomy, highlighting their potential for studying fast optical phenomena and measuring stellar diameters with unprecedented precision.

## Contribution

It shows that IACTs can be effectively used for high-resolution optical observations, including stellar diameter measurements, expanding their application beyond gamma-ray astronomy.

## Key findings

- First detection of asteroid occultations with an IACT
- Highest angular resolution measurements of stellar diameters in visible range
- Potential to increase measured stellar radii by 50% with a high-speed photometer

## Abstract

Imaging Atmospheric Cherenkov Telescopes (IACTs) are very-large telescopes designed to detect the nanosecond-timescale flashes produced within extended air showers. Because IACTs are sensitive to the Cherenkov light (UV/blue) and use photodetectors with extremely fast time responses, they are also able to perform simultaneous optical observations. The large reflecting areas of these telescopes (larger than 100 m$^2$) makes them well-suited to studying fast optical transient phenomena with timescales ranging from seconds to milliseconds to nanoseconds, and the unique optical design provides a wide field of view monitoring capability with a modest point spread function. VERITAS, with its recently upgraded PMT current monitoring instrumentation, was able to provide the first detection of asteroid occultations with an IACT, resulting in the highest angular resolution measurements for stellar diameters ever taken in the visible band range. Here we explore the feasibility of using this technique to significantly expand the number of stars with directly measured stellar radii, usable for population studies to test stellar evolution modelling or transiting exoplanet radius measurements. A single observatory with a high-speed visible-band photometer with a sensitivity reaching the 13$^{th}$ magnitude could increase the number of directly measured K stars diameters by 50%.