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Contact: F.X.Timmes
my one page vitae,
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Localized thermonuclear bursts from accreting magnetic white dwarfs (2022)

Nova explosions are caused by global thermonuclear runaways triggered in the surface layers of accreting white dwarfs. It has been predicted that localised thermonuclear bursts on white dwarfs can also take place, similar to Type I X-ray bursts observed in accreting neutron stars. Unexplained rapid bursts from the binary system TV Columbae, in which mass is accreted onto a moderately-strong magnetised white dwarf from a low-mass companion, have been observed on several occasions in the past ≈40 years. During these bursts the optical/UV luminosity increases by a factor of >3 in less than an hour and fades over ≈10 hours. Fast outflows have been observed in UV spectral lines$^{7}$, with velocities >3500 km/s, comparable to the escape velocity from the white dwarf surface. In this article, we report on optical bursts observed in TV Columbae as well as in two additional accreting systems, EI Ursae Majoris and ASASSN$-$19bh. The bursts have a total energy ≈10-6 those of classical nova explosions ("micronovae"), and bear a strong resemblance to Type I X-ray bursts. We exclude accretion or stellar magnetic reconnection events as their origin and suggest thermonuclear runaway events in magnetically-confined accretion columns as a viable explanation.

This article, made some news and some more news.


image
Optical brightness variations in TV Columbae
(a) TESS lightcurve, (b-d) 6.8 h of data around the three detected rapid bursts,
with individual bursts yielding integrated energies of 0.9e38 erg (b), 1.6e38 erg (c) and 1e38 erg (d).