Swift X-Ray Observations of Classical Novae. II. The Super Soft Source sample

TL;DR

This study utilizes Swift satellite data to analyze the X-ray evolution of 52 galactic and Magellanic Cloud novae, revealing patterns in super soft X-ray phases, variability, and correlations with optical phenomena, advancing understanding of nova outbursts.

Contribution

It provides the largest X-ray sample of novae to date, detailing their X-ray phases, variability, and challenging previous correlations, with new insights into optical-X-ray relationships.

Findings

Fast novae exhibit early hard X-ray phases often missing in slow novae.

Super Soft X-ray phases occur earlier and are shorter in fast novae.

Most novae cease nuclear burning within 3 years post-outburst.

Abstract

The Swift GRB satellite is an excellent facility for studying novae. Its rapid response time and sensitive X-ray detector provides an unparalleled opportunity to investigate the previously poorly sampled evolution of novae in the X-ray regime. This paper presents Swift observations of 52 Galactic/Magellanic Cloud novae. We included the XRT (0.3-10 keV) X-ray instrument count rates and the UVOT (1700-8000 Angstroms) filter photometry. Also included in the analysis are the publicly available pointed observations of 10 additional novae the X-ray archives. This is the largest X-ray sample of Galactic/Magellanic Cloud novae yet assembled and consists of 26 novae with super soft X-ray emission, 19 from Swift observations. The data set shows that the faster novae have an early hard X-ray phase that is usually missing in slower novae. The Super Soft X-ray phase occurs earlier and does not last as long in fast novae compared to slower novae. All the Swift novae with sufficient observations show that novae are highly variable with rapid variability and different periodicities. In the majority of cases, nuclear burning ceases less than 3 years after the outburst begins. Previous relationships, such as the nuclear burning duration vs. t_2 or the expansion velocity of the eject and nuclear burning duration vs. the orbital period, are shown to be poorly correlated with the full sample indicating that additional factors beyond the white dwarf mass and binary separation play important roles in the evolution of a nova outburst. Finally, we confirm two optical phenomena that are correlated with strong, soft X-ray emission which can be used to further increase the efficiency of X-ray campaigns.