An accreting white dwarf displaying fast transitional mode switching

TL;DR

This paper reports the discovery of rapid, large-amplitude mode switching in an accreting white dwarf system, revealing a new phenomenon linked to magnetic accretion processes similar to those in neutron stars.

Contribution

It introduces the first observation of fast mode switching in an accreting white dwarf, highlighting magnetic gating effects on short timescales.

Findings

Abrupt luminosity drops by up to 3.5 times within 30 minutes.

Identification of two distinct accretion modes with rapid switching.

Magnetically-gated accretion bursts observed in the low mode.

Abstract

Accreting white dwarfs are often found in close binary systems with orbital periods ranging from tens of minutes to several hours. In most cases, the accretion process is relatively steady, with significant modulations only occurring on time-scales of ~days or longer. Here, we report the discovery of abrupt drops in the optical luminosity of the accreting white dwarf binary system TW Pictoris by factors up to 3.5 on time-scales as short as 30 minutes. The optical light curve of this binary system obtained by the Transiting Exoplanet Survey Satellite (TESS) clearly displays fast switches between two distinct intensity modes that likely track the changing mass accretion rate onto the white dwarf. In the low mode, the system also displays magnetically-gated accretion bursts, which implies that a weak magnetic field of the white dwarf truncates the inner disk at the co-rotation radius in this mode. The properties of the mode switching observed in TW Pictoris appear analogous to those observed in transitional millisecond pulsars, where similar transitions occur, although on timescales of ~tens of seconds. Our discovery establishes a previously unrecognised phenomenon in accreting white dwarfs and suggests a tight link to the physics governing magnetic accretion onto neutron stars.