Contributed Talk - Splinter eROSITA

Tuesday, 13 September 2022, 14:44   (SFG 0140 / virtual eROSITA)

X-ray Detection of a Nova in the Fireball Phase

Ole König, Jörn Wilms, Riccardo Arcodia, Thomas Dauser, Konrad Dennerl, Victor Doroshenko, Frank Haberl, Steven Hämmerich, Christian Kirsch, Ingo Kreykenbohm, Maximilian Lorenz, Adam Malyali, Andrea Merloni, Arne Rau, Thomas Rauch, Gloria Sala, Axel Schwope, Valery Suleimanov, Philipp Weber, Klaus Werner
Remeis-Observatory & ECAP, FAU Erlangen-Nürnberg

Novae are caused by runaway thermonuclear burning in the hydrogen-rich envelopes of accreting white dwarfs, which leads to a rapid expansion of the envelope and the ejection of most of its mass. Theory has predicted the existence of a ‘fireball’ phase following directly on from the runaway fusion, which should be observable as a short, bright and soft X-ray flash before the nova becomes visible in the optical. I report of the discovery of this X-ray flash in the classical Galactic nova YZ Reticuli. The fireball phase happened 11 hours before the source's 9mag optical brightening. No X-ray source was detected 4h before and after the event, constraining the duration of the flash to shorter than 8h. In agreement with theoretical predictions, the source’s spectral shape is consistent with a black-body of 327,000 K (28.2 eV), or a white dwarf atmosphere, radiating at the Eddington luminosity, with a photosphere that is only slightly larger than a typical white dwarf. I also discuss a novel simulation approach to mitigate pile-up that was used to derive these results.