An Outburst by AM CVn binary SDSS J113732.32+405458.3

TL;DR

This paper reports the discovery of an outburst in the longest period AM CVn binary SDSS J113732.32+405458.3, revealing an unstable accretion disk and providing insights into its long-term behavior.

Contribution

First detection of an outburst in a long-period AM CVn binary, indicating unstable accretion disk behavior in such systems.

Findings

Observed a one magnitude brightness increase.

Outburst duration over approximately 300 days.

Recurrence time likely exceeds 12 years.

Abstract

We report the discovery of a one magnitude increase in the optical brightness of the 59.63 minute orbital period AM CVn binary SDSS J113732.32+405458.3. Public $g$, $r$, and $i$ band data from the Zwicky Transient Facility (ZTF) exhibit a decline over a 300 day period, while a few data points from commissioning show that the peak was likely seen. Such an outburst is likely due to a change in the state of the accretion disk, making this the longest period AM CVn binary to reveal an unstable accretion disk. The object is now back to its previously observed (by SDSS and PS-1) quiescent brightness that is likely set by the accreting white dwarf. Prior observations of this object also imply that the recurrence times for such outbursts are likely more than 12 years.