Optical and soft X-ray light-curve analysis during the 2022 eruption of U Scorpii: structural changes in the accretion disk
Abstract
We present our optical photometric observations of the 2022 eruption of the recurrent nova U Scorpii (U Sco) using 49,152 data points over 70 d following the optical peak. We have also analyzed its soft X-ray (0.3--1 keV) light curve by the Neil Gehrels Swift Observatory. During the 2022 eruption, the optical plateau stage started 13.8--15.0 d and ended 23.8--25.0 d after the optical peak. The soft X-ray stage started 14.6--15.3 d and ended 38.7--39.5 d after the optical peak. Both stages started later and had shorter durations, and the soft X-ray light curve peaked earlier and was less luminous compared to those during the U Sco 2010 eruption. These points suggest that there were differences in the envelope mass between the different cycles of the nova eruption. Furthermore, we have analyzed the optical eclipses during the 2022 eruption. The primary eclipse was first observed 10.4--11.6 d after the optical peak, earlier than the beginning of the optical plateau stage. This sequence of events can be explained by the receding ejecta photosphere associated with the expanding nova ejecta. We have determined the ingress and egress phases of the primary eclipses and estimated the outer radius of the optical light source centered at the white dwarf (WD). During the optical plateau stage, the source radius remained 1.2 times larger than the Roche volume radius of the primary WD, being close to the L1 point. When the optical plateau stage ended, the source radius drastically shrank to the tidal truncation radius within a few orbital periods. This previously unresolved phenomenon can be interpreted as a structural change in U Sco where the temporarily expanded accretion disk due to the nova wind returned to a steady state.
Cite
@article{arxiv.2402.06347,
title = {Optical and soft X-ray light-curve analysis during the 2022 eruption of U Scorpii: structural changes in the accretion disk},
author = {Katsuki Muraoka and Naoto Kojiguchi and Junpei Ito and Daisaku Nogami and Taichi Kato and Yusuke Tampo and Kenta Taguchi and Keisuke Isogai and Teofilo Arranz and John Blackwell and David Blane and Stephen M. Brincat and Graeme Coates and Walter Cooney and Shawn Dvorak and Charles Galdies and Daniel Glomski and Franz-Josef Hambsch and Barbara Harris and John Hodge and Jose L. Hernández-Verdejo and Marco Iozzi and Hiroshi Itoh and Seiichiro Kiyota and Darrell Lee and Magnus Larsson and Tapio Lahtinen and Gordon Myers and Berto Monard and Mario Morales Aimar and Masayuki Moriyama and Masanori Mizutani and Kazuo Nagai and Thabet AlQaissieh and Aldrin B. Gabuya and Mohammad Odeh and Carlos Perello and Andrew Pearce and Juan Miguel Perales and David Quiles and Filipp D. Romanov and David J. Lane and Michael Richmond and Nello Ruocco and Yasuo Sano and Mark Spearman and Richard Schmidt and Tonny Vanmunster and Pavol A. Dubovsky and Richard Wagner and Guido Wollenhaupt and Joachim Lorenz and Gerhard Lehmann and Andrea Salewski and Guy Williamson},
journal= {arXiv preprint arXiv:2402.06347},
year = {2024}
}
Comments
16 pages, 7 figures, 7 tables, accepted for publication in PASJ; doi:10.1093/pasj/psae010