Hot and dense water in the inner 25 au of SVS13-A

In the context of the ASAI (Astrochemical Surveys At IRAM) project, we carried out an unbiased spectral survey in the millimetre window towards the well known low-mass Class I source SVS13-A. The high sensitivity reached (3-12 mK) allowed us to detect at least six HDO broad (full width at half-maximum similar to 4-5 km s(-1)) emission lines with upper level energies up to E-u = 837 K. A non-local thermodynamic equilibrium Large Velocity Gradient (LVG) analysis implies the presence of very hot (150-260 K) and dense (>= 3 x 10(7) cm(-3)) gas inside a small radius (similar to 25 au) around the star, supporting, for the first time, the occurrence of a hot corino around a Class I protostar. The temperature is higher than expected for water molecules are sublimated from the icy dust mantles (similar to 100 K). Although we cannot exclude we are observing the effects of shocks and/or winds at such small scales, this could imply that the observed HDO emission is tracing the water abundance jump expected at temperatures similar to 220-250 K, when the activation barrier of the gas phase reactions leading to the formation of water can be overcome. We derive X(HDO) similar to 3 x 10(-6), and a H2O deuteration >= 1.5 x 10(-2), suggesting that water deuteration does not decrease as the protostar evolves from the Class 0 to the Class I stage.