The photon stream, a novel IACT event representation

Imaging Atmospheric Cherenkov Telescopes (IACTs) observe extensive air showers during the night to probe the very high energetic gamma ray sky on an event to event basis. Both a Cherenkov photon and a Night Sky Background (NSB) photon generates an indistinguishable electric pulse in IACT cameras. However, the separation of Cherenkov photons from the pool of NSB photons is crucial for the air shower reconstruction. Using silicon sensors, the single photon performance of the First G-APD Cherenkov Telescope (FACT) is stable enough that at least in dark nights a single photon reconstruction can be applied. This results in a list of photon arrival times for each pixel in contrast to the common main-pulse amplitude and main-pulse arrival time for each pixel. In this contribution, we first present our single photon extractor for FACT and evaluate its performance, second we introduce an IACT event representation which stores only the arrival times of the individual photons in each pixel (Photon Stream). Finally, we give a brief outlook into possible improvements in air shower reconstruction and show why the Photon Stream is a very natural IACT event format and why it has potential to be very compact, efficient and interchangeable.