Large-amplitude modulations and hours-timescale variability in the early X-ray light curve of a tidal disruption flare

¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748, Garching, Germany
² Università degli Studi di Milano, Via Giovanni Celoria 16, 20134, Milano, Italy
³ INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, I-20126, Milano, Italy
⁴ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716, Warszawa, Poland
⁵ International Centre for Radio Astronomy Research – Curtin University, GPO Box U1987, Perth, WA, 6845, Australia
⁶ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482, Potsdam, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 14 July 2025
Accepted: 11 February 2026

Abstract

We present new X-ray, optical, and UV observations of the tidal disruption event candidate eRASSt J234402.9−352640 (hereafter J2344). Between 50 and 60 days after peak optical brightness, J2344 exhibited large-amplitude modulations in its 0.2−2 keV emission, when the flux repeatedly dimed and re-brightened by a factor of ∼6 over a ∼3-day timescale. These modulations exhibited harder-when-brighter behaviour but were not detected in high-cadence observations obtained 60−70 days and 170−200 days after peak optical brightness, when the system instead exhibited stochastic X-ray variability over timescales of hours. We discuss the different physical mechanisms responsible for such exotic X-ray variability and explore the possibility that the modulations in J2344 were caused by the Lense-Thirring precession of the inner accretion flow around the disrupting black hole.