Bridging the Gap: OPTICAM Reveals the Hidden Spin of the WZ Sge Star GOTO 065054.49+593624.51

TL;DR

This paper reports high-cadence multi-band observations of the WZ Sge star GOTO 0650, revealing a potential white dwarf spin period of about 148 seconds during a dip in outburst, suggesting it bridges the gap between different types of intermediate polars.

Contribution

It presents the first detection of a possible white dwarf spin period in GOTO 0650, linking it to intermediate polars and providing insights into magnetic field effects in WZ Sge stars.

Findings

Detection of a 148-second signal in the blue band during the outburst dip.

The signal is interpreted as the white dwarf's spin period.

GOTO 0650 may connect intermediate and fast-rotating intermediate polars.

Abstract

WZ Sge stars are highly evolved accreting white dwarf systems (AWDs) exhibiting remarkably large amplitude outbursts (a.k.a. super-outbursts), typically followed by short rebrightenings/echo outbursts. These systems have some of the lowest mass transfer rates among AWDs, making even low magnetic fields dynamically important. Such magnetic fields are often invoked to explain the phenomenology observed in these systems, such as their X-ray luminosity and long periods of quiescence (30+ years). However, the detection of these is very elusive given the quenching of the accretion columns during outburst and the low luminosity of these systems during quiescence. Here we present high-cadence multi-band observations with {\it OPTICAM} of the recent outburst of the recently discovered WZ Sge star GOTO065054.49+593624.51, during the end of the main outburst and the dip in-between rebrightenings, covering 2 orders of magnitude in brightness. Our observations reveal the presence of a statistically significant signal with $P_{\omega}\simeq148$ seconds in the bluer ($g$) band which is detected only during the dip between the main outburst and the rebrigthenings. We interpret this signal as the spin period of the AWD. If confirmed, GOTO 0650 would bridge the gap between intermediate- and fast-rotating intermediate polars (IPs) below the period gap.