Pre-outburst signal in the light curves of the recurrent novae RS Oph and T CrB

Pre-outburst signal (a decrease of the optical brightness) just before the outburst is clearly detected in the observations of the T CrB obtained before and during the 1946 outburst. A similar decrease is also visible in the light curve of RS Oph during the 2021 outburst. We suppose that this is due to formation of a thick, dense envelope around the white dwarf, and we estimate its size (1000 - 2000 km), mass (5.10${}^{-8}$ - 6.10${}^{-7}$ M${}_{\odot }$) and average density (5 - 16 g cm${}^{-3}$).