On-sky silicon photomultiplier detector performance measurements for millisecond to sub-microsecond optical source variability studies

In our Ultra-Fast Astronomy (UFA) program, we aim to improve measurements of variability of astronomical targets on millisecond and shorter time scales. In this work, we present initial on-sky measurements of the performance of silicon photomultiplier detectors (SiPMs) for UFA. We mounted two different SiPMs at the focal plane of the 0.7-m aperture Nazarbayev University Transient Telescope at the Assy-Turgen Astrophysical Observatory, with no filter in front of the detector. The 3 mm x 3 mm SiPM single-channel detectors have a field of view of 2.2716 ' x 2.2716 '. During the nights of October 28-29, 2019, we measured sky background, bright stars, and an artificial source with a 100-Hz flashing frequency. We compared detected SiPM counts with Gaia satellite G-band flux values to show that our SiPMs have a linear response. With our two SiPMs (models S14520-3050VS and S14160-3050HS), we measured a dark current of similar to 130 and similar to 85 kilo counts per second (kcps), and a sky background of similar to 201 and similar to 203 kcps, respectively. We measured an intrinsic crosstalk of 10.34% and 10.52% and derived a 5 sigma sensitivity of 13.9 and 14 Gaia G-band magnitude for 200-ms exposures, for the two detectors, respectively. For a 10-mu s window, and allowing a false alarm rate of once per 100 nights, we derived a sensitivity of 22 detected photons, or six Gaia G-band magnitudes. For nanosecond timescales, our detection is limited by crosstalk to 12 detected photons, which corresponds to a fluence of similar to 155 photons per square meter. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)