Discovery of crested quasi-periodic eruptions following the most luminous SRG/eROSITA tidal disruption event

TL;DR

This paper reports the discovery of complex, quasi-periodic X-ray eruptions from a galactic nucleus, revealing new phenomenology that challenges existing models of such eruptions and suggesting possible links to extreme-mass-ratio inspirals.

Contribution

It introduces a new QPE source with unique crest flares, expanding the understanding of QPE phenomenology and its potential origins.

Findings

Detection of 12-hour quasi-periodic eruptions with 2-hour flares

Identification of hotter, shorter flares during QPE rising phases

Uncovering a new phenomenology challenging current QPE models

Abstract

We report the discovery of complex flaring activity from the galactic nucleus hosting the five-year-old tidal disruption event eRASSt J234402.9-352640 (J2344). With Einstein Probe and XMM-Newton observations, we detected highly structured soft X-ray variability. Through temporal decomposition of the XMM-Newton light curve and time-resolved spectral analysis, we identified broad, thermal flares recurring every $\sim$12 hours and lasting $\sim$2 hours, consistent with quasi-periodic eruptions (QPEs). Remarkably, these QPEs are accompanied by an unprecedented crest of hotter, shorter flares, each lasting between 5 and 30 minutes. These flares are predominantly found in the rising phases of the QPEs, although they also appear throughout the quiescence. These findings establish J2344 as a new member of the QPE emitter population and uncover a previously unobserved phenomenology that challenges current models of QPEs. In this letter, we present the phenomenological properties of this unique source and discuss possible interpretations within the framework of extreme-mass-ratio inspirals.