SiFAP4XP: Time domain polarimetry with silicon photometers at the TNG

SiFAP4XP is a new COTS PI instrument mounted at the TNG aimed at observing in the visible band some polarised objects simultaneously to the X-ray polarimetric mission IXPE. SiFAP4XP is an experience-based improvement over the previous version of the photometer SiFAP2 currently mounted at the F/11 focus of the TNG.SiFAP4XP takes advantage of the already installed polarimetric unit of Dolores, called PAOLO, based on a Wedged Double Wollaston prism to split the 4 position angles at increasing (45.) values from the N-S direction. Four pairs of Silicon MPPCs are mounted on both sides of a small optical bench and each pair of detectors receives from PAOLO the polarized light of the target and of the nearby sky through 8 optical relays. Another relay is dedicated to A&G. The control electronics are based on Red-Pitayas for photon counting, on GPS disciplined clocks for time tagging the photons with a resolution of 8ns. First light was at the end of February 2022.