In the last few years, short-term X-ray variability (of the order of hours) has been detected in a few supermassive black holes (SMBHs). Given the limited size of the sample, every new addition can bring invaluable information. Within the context of an automated search for X-ray sources showing flux variability in the ̧handra archive, we identified peculiar variability patterns in ( a SMBH in the Coma cluster, during observations performed in 2020. We investigated the long-term evolution of the flux, together with the evolution of the spectral parameters, throughout the ̧handra and observations, which cover a time span of approximately 20 years. We found that has repeatedly shown peculiar variability over the last 20 years, on typical timescales of simeq20-30,ks. From our spectral analysis, we found hints of a softer-when-brighter behaviour and of two well-separated flux states. We suggest that might represent a new addition to the ever-growing list of known relatively low-mass SMBHs (M showing extreme, possibly quasi-periodic X-ray variability on short timescales. The available dataset does not allow for a definitive classification of the nature of the variability. However, given the observed properties, it could either represent a quasi-periodic oscillation at a particularly low frequency or be associated with quasi-periodic eruptions in an active galactic nucleus with peculiar spectral properties.
Imbrogno et al. (Tue,) studied this question.