Speaker
Description
Despite the extraordinary leap forward obtained with current implementations on Imaging Air Cherenkov Telescopes (IACTs), which take advantage from the huge photon statistics, intensity interferometry on IACTs has to cope with the poor optical quality and large numerical aperture of the optics, which is a limiting factor for observations in narrow spectral bands and with sub-nanosecond accuracy. To improve on current Cherenkov implementations, we are realizing a new instrument, the Stellar Intensity Interferometry Instrument (SI3), to be installed on the ASTRI Mini-Array, an array of nine IACTs under construction in Tenerife, Spain. The assembly of the first instrument has been recently completed. ASTRI SI3 will lead to the first implementation of very narrow band, multi-channel intensity interferometry in photon counting on Cherenkov telescopes with a sub-nanosecond sampling time. The basic concept of SI3 is injecting light into a multimode optical fiber bundle at the telescope focal plane, working on the output beam to efficiently insert very narrow band (~1 nm) filters, and finally focussing light into modern single photon Silicon detectors fully exploiting their ~100 ps resolution. We demonstrated for the first time the feasibility of this concept with a prototype version of SI3 fully tested in the laboratory, which was capable of delivering a highly significant zero baseline narrow band measurement of the correlation from two Silicon Photon Multipliers (SiPM) detectors fed by multimode optical fibers. This result paves the way to significantly improving the boundaries and capabilities of stellar intensity interferometry with Cherenkov telescope arrays.
