Blazar variability with the Vera C. Rubin Legacy Survey of Space and Time (LSST)

With their emission mainly coming from a relativistic jet pointing towards us, blazars are fundamental sources to study extragalactic jets and their central engines, consisting of supermassive black holes (SMBHs) fed by accretion discs. They are also candidate sources of high-energy neutrinos and cosmic rays. Because of the jet orientation, the non-thermal blazar emission is Doppler beamed; its variability is unpredictable and occurs on time-scales from less than one hour to years. The comprehension of the diverse mechanisms producing the flux and spectral changes requires well-sampled multiband light curves on long time periods. In particular, outbursts are the best test bench to shed light on the underlying physics, especially when studied in a multiwavelength context. The Vera C. Rubin Legacy Survey of Space and Time (Rubin-LSST) will monitor the southern sky for ten years in six photometric bands, offering a formidable tool to study blazar variability features in a statistical way. The alert system will allow us to trigger follow-up observations of outstanding events, especially at high (keV-to-GeV) and very high (TeV) energies. We here examine the simulated Rubin-LSST survey strategies with the aim of understanding which cadences are more suitable for the blazar variability science. Our metrics include light curve and colour sampling. We also investigate the problem of saturation, which will affect the brightest and many flaring sources, and will have a detrimental impact on follow-up observations.