Using the Neutron Star Interior Composition Explorer (NICER) and various ground-based telescopes, an international team of astronomers observed a powerful X-ray superflare occurring in 2022 at a giant star known as HD 251108. Results of the monitoring campaign were published on the preprint server on October 4 arXivThis provides more information about the star’s active activity.

Superflares are powerful bursts of energy coming from the surface of stars. Detection and detailed examination of such new flares are important to better understand the origin of these events and the interaction between magnetic fields and stellar surfaces.

Located approximately 1,646 light-years away, HD 251108 is an advanced and magnetically active K-type giant star approximately seven times the mass of the Sun. The star is relatively cool, with an effective temperature of 4460 K, and its mass is comparable to that of the Sun.

In late 2022, HD 251108 underwent a powerful X-ray superflare, and a team of astronomers led by Hans Moritz Günther of MIT’s Kavli Institute for Astrophysics and Space Studies in Cambridge, Massachusetts, began observing the event to better understand the single-light flare activity. . giant stars.

“We tracked the decay phase of the superflare for 28 days with NICER and from the ground. We track the decay of the flare in unprecedented detail in various components of the coronal temperature,” the researchers write in the paper.

Observations showed that the 2022 superflare in HD 251108 has a peak flux of approximately 10 decir erg/s in the 0.5-4.0 keV range and an exponential decay time of 2.2 days in the early decay phase. This makes it one of the most powerful flares ever observed.

Based on the data collected, the length of the flare ring was estimated to be two to four times the radius of HD 251108. Additionally, approximately 10 days after the peak of the flare, the flare appeared to go through a brief phase of limited recurrence. -Heating and the light curve began to deviate from the initial distortion.

The study found that the chemical composition of HD 251108 was constant throughout the explosion, consistent with typical active stars with an inverse first ionization potential (IFIP) effect. The astronomers noted that during the initial decay, the X-ray light curve corresponded to a weakening of the hydrogen alpha flux, while the plasma showed some reheating.

According to the paper, HD 251108 exhibits spin modulation with a period of 21.3 days. This behavior can be explained by large starspots that remain stationary for several years but rotate within the field of view. Observations also revealed that the star exhibits photometric variability of around magnitude 0.5 on timescales of one or more decades. This is consistent with these large and very stable starspots.