2025MNRAS.543.1146B

Superbursts are rare events observed from bursting neutron star low-mass X-ray binaries. They are thought to originate from unstable burning of the thick layer of Carbon on the surface of the neutron star, causing the observed X-ray flashes to last several hours. Given their fluence it has long been thought that superbursts may have significant effects on the accretion flow around the neutron star. In this paper, we first present evidence for a new superburst observed from 4U 1608-522 by Monitor of All-sky X-ray Image (MAXI) during the 2020 outburst, around 00:45 UTC on 2020 July 16. We compare some of the properties of this superburst and the underlying outburst with the events recorded on 2005 May 5 by Rossi X-ray Timing Explorer (RXTE) and most recently in 2025 by MAXI. We then present our spectral analysis of Neutron star Interior Composition Explorer (NICER) and Insight-HXMT data obtained before and after the 2020 superburst event. Our results indicate that the inner disc temperature and the radius show a systematic evolution in the following few days, which may be related to the superburst. We show that the time-scale of the observed evolution can not be governed by viscous time-scales unless the viscosity parameter is unrealistically low.