Two luminous flares detected from a nearby tidal disruption event

A group of astronomers from numerous institutions have investigated a recently discovered nearby tidal disruption event known as ASASSN-22ci. They detected two luminous flares from this event. The finding was reported in a paper published Dec. 19 on the preprint server arXiv.

Tidal disruption events (TDEs) are astronomical phenomena that occur when a star passes close enough to a supermassive black hole and is pulled apart by the black hole’s tidal forces, causing the process of disruption.

Such tidally disrupted stellar debris starts raining down on the black hole and radiation emerges from the innermost region of accreting debris, which is an indicator of the presence of a TDE. All in all, the debris stream–stream collision causes an energy dissipation, which may lead to the formation of an accretion disk.

Therefore, TDEs are perceived by astronomers as potentially important probes of strong gravity and accretion physics, providing answers about the formation and evolution of supermassive black holes.

ASASSN-22ci (also known as AT2022dbl) is a TDE discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) in February 2022. It occurred in the nucleus of a galaxy designated WISEA J122045.05+493304.7, at a redshift of approximately 0.0284.

Shortly after the discovery, a team of astronomers led by University of Hawaii’s Jason T. Hinkle commenced spectroscopic and photometric follow-up observations of ASASSN-22ci with the Zwicky Transient Facility (ZTF), Asteroid Terrestrial Impact Last Alert System (ATLAS), and ASAS-SN. This resulted in the detection of two flares from the source.

According to the paper, each of the two flares has a temperature of about 30,000 K, a rising time of approximately 30 days, and a peak bolometric luminosity at a level of 200–1,000 tredecillion erg/s. They also showcase a blue optical spectrum with broad hydrogen, helium, and nitrogen lines. The second flare occurred some 720 days after the first one.

The astronomers noted that pre-discovery survey observations of ASASSN-22ci rule out the existence of earlier flares within the past 6,000 days, which suggests that the discovery of this TDE likely coincides with the first flare. They predict that the next flare of ASASSN-22ci should occur near February 4, 2026.

The discovery made by Hinkle’s team makes ASASSN-22ci one of only five TDEs that have been reported to experience multiple flares. The researchers added that its two flares have good coverage with multiwavelength photometry and high signal-to-noise optical spectroscopy, when compared to other multiple-flaring TDEs.

“We have now observed five optically-selected TDEs that exhibit multiple flares, some of which are likely to be repeating partial tidal disruptions. Although small, this sample is nevertheless sufficient to begin exploring the theoretical implications of the observed trends among these events,” the authors of the paper concluded.

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