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

TL;DR

The paper reports the discovery of crested quasi-periodic eruptions in J2344, a galaxy hosting a five-year-old TDE-like event, using Einstein Probe and XMM-Newton X-ray data. It identifies a pair of broad, recurring QPEs separated by about t_rec ≈ 12 h, with each eruption displaying a typical duration of width ≈ 0.43 h, and a novel crest of narrow, hotter, short-duration flares (5–30 minutes) that peaks during the rising phases of the broad flares. Time-resolved spectroscopy shows broad flares follow the canonical hysteresis cycle in the L_bol–T plane, while narrow flares exhibit different spectral evolution including a colder-when-brighter trend, not seen in standard QPEs. Interpreting these results within extreme mass ratio inspiral (EMRI) scenarios, the authors propose that disk ejecta drive broad QPEs and stellar debris or an intermediate-mass black hole may generate the narrow-flare crest, highlighting the need for new theoretical work and continued monitoring to constrain the mechanism behind QPEs and their connection to TDEs.

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.

Figures (8)

• Figure 1: XMM-Newton EPIC-pn 0.2--10 keV light curve of J2344. The source count rates are shown in black, while the background is plotted in blue. Due to the selected observing strategy, only short snapshots spaced by several hours are available for EP.
• Figure 2: Best fit of the XMM-Newton flare profiles. We do not find significant evidence of asymmetry; therefore, we use Gaussian functions. In the top two panels, we show the temperature and bolometric luminosity evolution along the flares, derived from time-resolved spectral analysis. The blue points correspond to data extracted during the short-time flares, while the green points trace the evolution of the broad underlying flares.
• Figure 3: Spectral evolution of the broad component (green) and of the three stacked narrow flares of E-2 (blue). While the broad component evolves counterclockwise, consistent with typical QPE behavior, the narrow flares show the opposite behavior.
• Figure 4: Duration vs. recurrence time relation for all known QPEs. The black contours represent the newly added J2344. We conservatively estimate a lower limit on the recurrence time of $11.7/2\,$h. This accounts for the possibility of missing an intermediate broad flare, due to modulations of the QPE amplitude (e.g., giustini2024). The top left shaded area corresponds to a duration time greater than or equal to the recurrence time.
• Figure 5: Different time bins extracted for the XMM-Newton pn light curve. The different panels represent (from top to bottom) the time bins for E-1, F-1 and F-2, E-2, and E-3. The results of the spectral analysis can be found in Table \ref{['tab:spec']}