NICER / ISS Science Nugget for May 24, 2018

Target of Opportunity observations of new transient ASASSN-18el

This week, NICER responded to an extreme nuclear transient associated with a known active galaxy (of the "Seyfert 2" class). This extreme accretion event may be due to a "tidal disruption event" (TDE), where a star has ventured too close to the galaxy's central black hole. TDEs are near-pristine laboratories of relativistic accretion.

NICER observed the target ASASSN-18el, discovered by the All Sky Automated Survey for SuperNovae (ASAS-SN) collection of telescopes distributed around the world. NICER investigations can help us understand the nature of this extreme accretion event, and can yield black hole masses, spins, and inclinations from TDEs, together with the structure of the extreme gravitational field just outside the event horizon of a black hole that was previously unobservable.

Figure: The X-ray spectrum (left) and light curve (right) of ASASSN-18el as observed by NICER.
Both are consistent with a 150 eV blackbody.

NICER will continue to observe this object and the science team is analyzing the data to determine the nature of this unusual X-ray activity.

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