Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow
Dheeraj R. Pasham (MIT), Wynn C. G. Ho, William Alston, Ronald, Remillard, Mason Ng, Keith Gendreau, Brian D. Metzger, Diego Altamirano,, Deepto Chakrabarty, Andrew Fabian, Jon Miller, Peter Bult, Zaven Arzoumanian,, James F. Steiner, Tod Strohmayer, Francesco Tombesi

TL;DR
This paper presents evidence of a high-frequency quasi-periodic oscillation in the X-ray emission of the transient AT2018cow, suggesting the presence of a compact object such as a neutron star or black hole.
Contribution
The study provides the first detection of a QPO in an FBOT, indicating a compact object and offering new insights into the nature of these explosive events.
Findings
Detection of a 224 Hz QPO in AT2018cow's X-ray emission
QPO persists over the entire 60-day outburst
Implying a compact object with mass less than 850 solar masses
Abstract
The brightest Fast Blue Optical Transients (FBOTs) are mysterious extragalactic explosions that may represent a new class of astrophysical phenomena. Their fast time to maximum brightness of less than a week and decline over several months and atypical optical spectra and evolution are difficult to explain within the context of core-collapse of massive stars which are powered by radioactive decay of Nickel-56 and evolve more slowly. AT2018cow (at redshift of 0.014) is an extreme FBOT in terms of rapid evolution and high luminosities. Here we present evidence for a high-amplitude quasi-periodic oscillation (QPO) of AT2018cow's soft X-rays with a frequency of 224 Hz (at 3.7 significance level or false alarm probability of 0.02%) and fractional root-mean-squared amplitude of >30%. This signal is found in the average power density spectrum taken over the entire 60-day outburst and…
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