Multi-mission results on RS Oph observed in X-rays: a unique view of the white dwarf and the outflow.

Novae are powerful eruptions on the surface of a white dwarf in a binary systems, triggered by a thermonuclear runaway on material accreted from a close binary companion. In the recurrent novae, the outburst has been observed at least twice on time scales of 1 to 100 years, during human lifetimes. "Symbiotic novae" are those in long period systems, with a red giant or asymptotic giant branch companion and orbital periods of the order of years (instead of hours like in cataclysmic variables). RS Oph, both a recurrent and a symbiotic nova, had its 7th recorded outburst in 2021 August. As an already well monitored, luminous nova that hosts a massive white dwarf and is a possible type Ia supernova candidate progenitors, it aroused great interest and was monitored at all wavelengths, from radio to gamma-rays. I led three projects with different groups: long term, intense monitoring with NICER, grating spectra of the shocked ejecta with Chandra and XMM-Newton, and a NuSTAR exposure 10 days after maximum, when gamma-ray emission was still copious. I also participated in other projects with Swift and XMM-Newton. I will report here on the evolution of the nova during outbursts: an intriguing delay between X-ray and gamma-ray maximum that seems to imply multiple shock sites, the emergence of the hydrogen burning, hot white dwarf while a soft X-ray spectrum was still measured from the ejecta, the intriguing 35 s pulsation of the white dwarf, always clearly measured with NICER, with an initially "drifting" period that seemed to stabilize towards the end of the outburst, and the outflow spectrum during the late phase of the eruption.