# The supersoft X-ray transient ASASSN-16oh as a thermonuclear runaway without mass ejection

## TL;DR

The paper proposes that the transient ASASSN-16oh was caused by a thermonuclear runaway on a white dwarf without mass ejection, challenging previous accretion-based interpretations and predicting future outbursts for confirmation.

## Contribution

It demonstrates that the transient can be explained as a non-ejective thermonuclear event, providing a new perspective on its origin and suggesting observational tests for future outbursts.

## Key findings

- Event characteristics match non-mass ejecting thermonuclear runaways.
- Optically thick accretion disk likely hides the white dwarf surface.
- Predicted outburst within 10-15 years for observational confirmation.

## Abstract

The supersoft X-ray and optical transient ASASSN-16oh has been interpreted by Maccarone et al. (2019) as having being induced by an accretion event on a massive white dwarf, resembling a dwarf nova super-outburst. These authors argued that the supersoft X-ray spectrum had a different origin than in an atmosphere heated by shell nuclear burning, because no mass was ejected. We find instead that the event's timescale and other characteristics are typical of non-mass ejecting thermonuclear runaways, as already predicted by Shara et al. (1977) and the extensive grid of nova models by Yaron et al. (2005). We suggest that the low X-ray and bolometric luminosity in comparison to the predictions of the models of nuclear burning are due to an optically thick accretion disk, hiding most of the white dwarf surface. If this is the case, we calculated that the optical transient can be explained as a non-ejective thermonuclear event on a WD of $\simeq$1.1M$_\odot$ accreting at the rate of $\simeq3.5{-}5{\times}10^{-7}$M$_\odot$yr$^{-1}$. We make predictions that should prove whether the nature of the transient event was due to thermonuclear burning or to accretion; observational proof should be obtained in the next few years, because a new outburst should occur within $\simeq$10-15 years of the event.