Performance of MAGIC stellar intensity interferometer and expansion to MAGIC + CTAO-LST1 stellar intensity interferometer

TL;DR

This paper discusses the development and performance of the MAGIC stellar intensity interferometer, its recent scientific achievements, and the expansion to include CTAO-LST1, demonstrating the feasibility of a larger, more capable SII system.

Contribution

It introduces the upgraded MAGIC SII system, reports its first scientific results, and presents a plan to expand the system with CTAO-LST1 and additional telescopes.

Findings

Measured angular sizes of 22 stars, 13 without previous B band measurements.

MAGIC SII can switch quickly between gamma-ray and SII modes.

Successful correlation measurements with CTAO-LST1 in early 2024.

Abstract

A new generation of optical intensity interferometers are emerging in recent years taking advantage of the existing infrastructure of Imaging Atmospheric Cherenkov Telescopes (IACTs). The MAGIC SII (Stellar Intensity Interferometer) in La Palma, Spain, has been operating since its first successful measurements in 2019 and its current design allows it to operate regularly. The current setup is ready to follow up on bright optical transients, as changing from regular gamma-ray observations to SII mode can be done in a matter of minutes. A paper studying the system performance, first measurements and future upgrades has been recently published. MAGIC SII's first scientific results are the measurement of the angular size of 22 stars, 13 of which with no previous measurements in the B band. More recently the Large Sized Telescope prototype from the Cherenkov Telescope Array Observatory (CTAOLST1) has been upgraded to operate together with MAGIC as a SII, leading to its first correlation measurements at the beginning of 2024. MAGIC+CTAO-LST1 SII will be further upgraded by adding the remaining CTAOLSTs at the north site to the system (which are foreseen to be built by the end of 2025). MAGIC+CTAO-LST1 SII shows a feasible technical solution to extend SII to the whole CTAO.