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We implement an electron avalanche photodiode (e-APD) in the MIRC-Xinstrument, upgrade of the 6-telescope near-infrared imager MIRC, at the CHARAarray. This technology should improve the sensitivity of near-infraredinterferometry. We first used the classical Mean-Variance analysis to measurethe system gain and the amplification gain. We then developed a physical modelof the statistical distribution of the camera output signal. This model isbased on multiple convolutions of the Poisson statistic, the intrinsicavalanche gain distribution, and the observed distribution of the backgroundsignal. At low flux level, this model constraints independently the incidentillumination level, the total gain, and the excess noise factor of theamplification. We measure a total transmission of $48\pm3\%$ including the coldfilter and the Quantum Efficiency. We measure a system gain of 0.49 ADU/e, areadout noise of $10$ ADU, and amplification gains as high as 200. Theseresults are consistent between the two methods and therefore validate ourmodeling approach. The measured excess noise factor based on the modeling is$1.47\pm0.03$, with no obvious dependency with flux level or amplificationgain. The presented model allows measuring the characteristics of the e-APDarray at low flux level independently of preexisting calibration. With$<0.3$\,electron equivalent readout noise at kilohertz frame rates, we confirmthe revolutionary performances of the camera with respect to the PICNIC orHAWAII technologies. However, the measured excess noise factor is significantlyhigher than the one claimed in the literature ($<$1.25), and explains whycounting multiple photons remains challenging with this camera.

astronomy and astrophysics

Modeling the e-APD SAPHIRA/C-RED ONE camera at low flux level: an  attempt of photon counting in the near-infrared with the MIRC-X  interferometric combiner