The first confirmed superoutburst of the dwarf nova GALEX J215818.5+241924

TL;DR

This paper reports the first confirmed superoutburst of the dwarf nova GALEX J215818.5+241924, detailing its superhump behavior, period evolution, and classification as an SU UMa type dwarf nova based on photometric observations.

Contribution

First detection and detailed analysis of a superoutburst in GALEX J215818.5+241924, including superhump period evolution and orbital period estimation.

Findings

Superoutburst lasted at least 10 days with a 4.6 magnitude amplitude.

Superhump period was approximately 0.06728 days, with a notable period evolution during the outburst.

Estimated orbital period is about 0.06606 days, consistent with SU UMa dwarf novae.

Abstract

In 2011 October an optical transient was reported in Pegasus as a possible nova. The object had an ultraviolet counterpart, GALEX J215818.5+241924. In this paper we present follow-up photometry of the object which revealed the presence of superhumps, with peak-to-peak amplitude of up to 0.22 magnitudes, diagnostic of it being a member of the SU UMa family of dwarf novae. The outburst amplitude was 4.6 magnitudes and it lasted at least 10 days, with a maximum brightness of magnitude 14.3. We determined the mean superhump period from our first 5 nights of observations as Psh = 0.06728(21) d. However analysis of the O-C residuals showed a dramatic evolution in Psh during the outburst. During the first part of the plateau phase the period increased with dPsh/dt = +2.67(15) x 10-4. There was then an abrupt change following which the period decreased with dPsh/dt = -2.08(9)x 10-4. We found a signal in the power spectrum of the photometry which we tentatively interpret as the orbital signal with Porb = 0.06606(35) d. Thus the superhump period excess was epsilon = 0.020(8), such value being consistent with other SU UMa systems of similar orbital period.