First measurements and upgrade plans of the MAGIC intensity interferometer

TL;DR

This paper discusses the first measurements and upgrade plans for the MAGIC intensity interferometer, which uses Cherenkov telescopes to measure stellar diameters with high sensitivity and plans to expand with additional telescopes for improved coverage.

Contribution

It introduces a novel intensity interferometer setup using MAGIC telescopes with GPU-based real-time correlator and plans to integrate CTA telescopes for enhanced capabilities.

Findings

Achieved stellar diameter measurements with 10x better sensitivity than 1970s

Implemented active mirror control for simultaneous multi-baseline measurements

Plans to incorporate CTA LST-1 to improve sensitivity and u-v coverage

Abstract

The two MAGIC 17-m diameter Imaging Atmospheric Cherenkov Telescopes have been equipped to work also as an intensity interferometer with a deadtime-free, 4-channel, GPU-based, real-time correlator. Operating with baselines between approx. 40 and 90 m the MAGIC interferometer is able to measure stellar diameters of 0.5-1 mas in the 400-440 nm wavelength range with a sensitivity roughly 10 times better than that achieved in the 1970s by the Narrabri Stellar Intensity Interferometer. Besides, active mirror control allows to split the primary mirrors into sub-mirrors. This allows to make simultaneous calibration measurements of the zero-baseline correlation or to simultaneously collect six baselines below 17 m with almost arbitrary orientation, corresponding to angular scales of approx. 1-50 mas. We plan to perform test observations adding the nearby Cherenkov Telescope Array (CTA) LST-1 23 m diameter telescope by next year. All three telescope pairs will be correlated simultaneously. Adding LST-1 is expected to increase the sensitivity by at least 1 mag and significantly improve the u-v plane coverage. If successful, the proposed correlator setup is scalable enough to be implemented to the full CTA arrays.