SIMBAD references

The Intensity Interferometry Imaging Telescope (I3T) concept illustrated how a single imaging air Cherenkov telescope (IACT) can be transformed into a multi-element intensity interferometer. This is achieved by segmenting the light collecting surface into many sub-apertures via active control of individual mirror facets. Here, we propose an alternative method applicable to all IACTs that we refer to as pupil plane intensity interferometry. Principally, the re-imaged pupil of an IACT can be subdivided with a multipixel detector to enable extremely dense uv-plane sampling. Ray tracing of an IACT based on one of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) light collectors was performed as a proof of principle. Several unique science cases could be investigated and, in particular, we performed a case study that indicates the ability to strongly constrain the angular brightness distribution of the extended disc of the Be star Gamma Cassiopeia. The proposed design could be used as an alternative to current intensity interferometry instruments as it mitigates several inherent limitations of IACTs when used as intensity interferometers, namely temporal dispersion and large angular point spread functions.