Swift X-ray and UV observations of SDSS J141118.31+481257.6 during its first ever recorded superoutburst

Abstract

SDSS J141118.31+481257.6 is an ultracompact white dwarf binary (or AM CVn system) with an orbital period of 46 min. We analyse ∼23 ks of X-ray and ultraviolet (UV) data taken with the Neil Gehrels Swift Observatory during its first ever recorded outbursts. The events took place 13 yr after the system was discovered. We detected three events in our UV data, all with amplitudes of ∼7 mag with respect to quiescence, the largest detected for an AM CVn system so far. The first two events correspond to a superoutburst and the third one to another detected outburst. The three episodes that we identified occurred in a period of 24 d, each one displaying very rapid brightness changes. At ∼120 d since the detection of the superoutburst, the system remains 1 mag brighter in UV compared to the quiescence level. The X-ray observations suggest that the X-ray emission is not correlated with the UV.