2023MNRAS.518.3428W

Following the discovery of a new class of X-ray variability seen in four galaxies, dubbed quasi-periodic eruptions (QPEs), we reconsider the variability seen in the low-mass active galactic nucleus (AGN) 2XMM J123103.2+110648 to ascertain whether it should be considered a QPE host galaxy. We apply the autocorrelation function to two archival XMM-Newton observations to determine characteristic time-scales for variability of ∼13.52 and ∼14.35 ks. The modelling of light curves, both folded at these time-scales and unfolded, indicates that a Gaussian model is preferable over a sinusoidal model, with average durations for the bright phases of 6.17 and 7.69 ks. In a broad 0.2-1.0 keV band the average amplitude of the bright phases was found to be 2.86 and 8.56 times the quiescent count rate. The pattern of variability seen in 2XMM J123103.2+110648 cannot be definitively declared as a series of QPEs. Instead, this suggests there may be a continuum of quasi-periodic variability ranging from eruptions to oscillations being caused by a single mechanism. This offers the possibility of finding further sources that continue to bridge the gap between QPEs and quasi-periodic oscillations (QPOs). A targeted analysis of 47 observations of 11 other low-mass AGN (log (M_BH) ≲ 6) found no evidence of QPE- or QPO-like behaviour in a sample of other similar mass objects.