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The solar telescope connected to HARPS-N has been observing the Sun since thesummer of 2015. Such high-cadence, long-baseline data set is crucial forunderstanding spurious radial-velocity signals induced by our Sun and by theinstrument. On the instrumental side, this data set allowed us to detectsub-\ms\,systematics that needed to be corrected for. The goal of thismanuscript is to i) present a new data reduction software for HARPS-N, ii)demonstrate the improvement brought by this new software on the first threeyears of the HARPS-N solar data set, and iii) release all the obtained solarproducts, from extracted spectra to precise radial velocities. To correct forthe instrumental systematics observed in the data reduced with the currentversion of the HARPS-N data reduction software (DRS version 3.7), we adaptedthe newly available ESPRESSO DRS (version 2.2.3) to HARPS-N and developed newoptimized recipes for the spectrograph. We then compared the first three yearsof HARPS-N solar data reduced with the current and new DRS. The mostsignificant improvement brought by the new DRS is a strong decrease in theday-to-day radial-velocity scatter, from 1.27 to 1.07\ms; this is thanks to amore robust method to derive wavelength solutions, but also to the use ofcalibrations closer in time. The newly derived solar radial-velocities are alsobetter correlated with the chromospheric activity level of the Sun on thelong-term, with a Pearson correlation coefficient of 0.93 compared to 0.77before, which is expected from our understanding of stellar signals. Finally,we also discuss how HARPS-N spectral ghosts contaminate the measurement of thecalcium activity index, and present an efficient technique to derive an indexfree of instrumental systematics. This paper presents a new data reductionsoftware for HARPS-N, and demonstrates its improvements [...]

Three Years of HARPS-N High-Resolution Spectroscopy and Precise Radial Velocity Data for the Sun