Journal Article

X-ray detection of a nova in the fireball phase

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

2022

Overview

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 1 , 2 . 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 3 – 5 . Here we report observations of a bright and soft X-ray flash associated with the classical Galactic nova YZ Reticuli 11 h before its 9 mag optical brightening. No X-ray source was detected 4 h before and after the event, constraining the duration of the flash to shorter than 8 h. In agreement with theoretical predictions 4 , 6 – 8 , the source’s spectral shape is consistent with a black-body of 3.27 +0.11 −0.33  × 10 5  K (28.2 +0.9 −2.8  eV), or a white dwarf atmosphere, radiating at the Eddington luminosity, with a photosphere that is only slightly larger than a typical white dwarf. 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 1 , 2 . 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 3 – 5 . Here we report observations of a bright and soft X-ray flash associated with the classical Galactic nova YZ Reticuli 11 h before its 9 mag optical brightening. No X-ray source was detected 4 h before and after the event, constraining the duration of the flash to shorter than 8 h. In agreement with theoretical predictions 4 , 6 – 8 , the source’s spectral shape is consistent with a black-body of 3.27 +0.11 −0.33  × 10 5  K (28.2 +0.9 −2.8  eV), or a white dwarf atmosphere, radiating at the Eddington luminosity, with a photosphere that is only slightly larger than a typical white dwarf.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/33/34/4118 / 639/33/34/4127 / 639/33/34/864 / Atmosphere / Blackbody / Brightening / Burning / Deposition / Dwarf novae / Fireballs / Humanities and Social Sciences / Hydrogen / Luminosity / multidisciplinary / Novae / Photosphere / Science / Science (multidisciplinary) / Soft x rays / Stellar atmospheres / White dwarf stars / X ray flashes / X ray sources / X-Rays