Blazars through the eyes of REDSoX and GOSoX

Blazar polarimetric properties provide key constraints on the physical conditions within relativistic jets, offering insights into particle acceleration mechanisms, high-energy radiation processes, and jet composition. The Rocket Experiment Demonstration of a Soft X-ray Polarimeter (REDSoX) will serve as a precursor to the Globe Orbiting Soft X-ray Polarimeter (GOSoX), a state-of-the-art polarimeter designed for observations in the soft X-ray range (0.2–0.4 keV), with a planned launch for 2030. REDSoX and GOSoX will be the first (and currently only) X-ray polarimeters capable of performing observations below 1 keV, opening a new observational window into high-energy polarimetry. In this work, we investigate the soft X-ray polarimetric properties of blazars expected in the REDSoX and GOSoX band and assess the detectability of different samples of sources: one drawn from the RoboPol Monitoring Program, a statistically complete sample of γ-ray-selected blazars spanning the low-, intermediate-, and high-synchrotron-peaked sources, and one cross-matched between the CAZ (CRTS, ATLAS, and ZTF) and eROSITA catalogs. We estimated the expected source fluxes in the selected energy bands through spectral energy distribution fitting performed with the tool. We investigated the expected polarimetric properties under three competing emission scenarios: leptonic, hadronic, and hybrid, each one predicting distinct observational signatures. We assessed the detectability of every source by comparing our polarization degree predictions with the instrument's minimum detectable polarization function (MDP). Finally, we computed the detection probability for each source. This work offers a set of promising blazar targets for future observations with GOSoX, highlighting the mission’s potential for probing relativistic jet physics through soft X-ray polarimetry. Bjet-MCMC