Ultraviolet and X-ray light-curves of novae observed by the Neil Gehrels Swift Observatory

TL;DR

This paper presents a uniform analysis of ultraviolet light-curves of 12 novae observed by Swift, revealing power-law decay behaviors and correlations between UV and X-ray emissions, with no significant differences across nova types.

Contribution

First comprehensive analysis of UV light-curves of novae from Swift, demonstrating consistent decay patterns and linking UV/X-ray evolution across different nova populations.

Findings

UV light-curves follow power-law decay.

X-ray emission drops significantly after nuclear burning ends.

UV decline is less steep and often shows a break coinciding with X-ray decline.

Abstract

With rapid response capabilities, and a daily planning of its observing schedule, the Neil Gehrels Swift Observatory is ideal for monitoring transient and variable sources. Here we present a sample of the 12 novae with the most detailed ultraviolet (UV) follow-up by Swift -- the first uniform analysis of such UV light-curves. The fading of these specific light-curves can be modelled as power-law decays (plotting magnitude against log time), showing that the same physical processes dominate the UV emission for extended time intervals in individual objects. After the end of the nuclear burning interval, the X-ray emission drops significantly, fading by a factor of around 10-100. The UV changes, however, are of a lower amplitude, declining by 1-2 mag over the same time period. The UV light-curves typically show a break from flatter to steeper around the time at which the X-ray light-curve starts a steady decline from maximum, ~0.7-1.3 T_SSSend. Considering populations of both classical and recurrent novae, and those with main sequence or giant companions, we do not find any strong differences in the UV light-curves or their evolution, although the long-period recurrent novae are more luminous than the majority of the classical novae.