Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow

Dheeraj R. Pasham; 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; Jeroen Homan; Edward M. Cackett; Alice Harding

doi:10.1038/s41550-021-01524-8

Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow

Dheeraj R. Pasham, 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, Jeroen Homan, Edward M. Cackett, Alice Harding

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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$\sigma$ 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 suggests a highly persistent signal that lasts for a billion cycles. The high frequency (rapid timescale) of 224 Hz (4.4 ms) argues for a compact object in AT2018cow, which can be a neutron star or black hole with a mass less than 850 solar masses. If the QPO is the spin period of a neutron star, we can set limits on the star's magnetic field strength. Our work highlights a new way of using high time-resolution X-ray observations to study FBOTs.

Original language	English
Journal	Nature Astronomy
DOIs	https://doi.org/10.1038/s41550-021-01524-8
Publication status	Published - 8 Dec 2021

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astro-ph.HE

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Pasham, D. R., Ho, W. C. G., Alston, W., Remillard, R., Ng, M., Gendreau, K., Metzger, B. D., Altamirano, D., Chakrabarty, D., Fabian, A., Miller, J., Bult, P., Arzoumanian, Z., Steiner, J. F., Strohmayer, T., Tombesi, F., Homan, J., Cackett, E. M., & Harding, A. (2021). Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow. Nature Astronomy. https://doi.org/10.1038/s41550-021-01524-8

@article{2473c4711563494c98173e0b0e7da293,

title = "Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow",

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$\sigma$ 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 suggests a highly persistent signal that lasts for a billion cycles. The high frequency (rapid timescale) of 224 Hz (4.4 ms) argues for a compact object in AT2018cow, which can be a neutron star or black hole with a mass less than 850 solar masses. If the QPO is the spin period of a neutron star, we can set limits on the star's magnetic field strength. Our work highlights a new way of using high time-resolution X-ray observations to study FBOTs.",

keywords = "astro-ph.HE",

author = "Pasham, {Dheeraj R.} and Ho, {Wynn C. G.} and William Alston and Ronald Remillard and Mason Ng and Keith Gendreau and Metzger, {Brian D.} and Diego Altamirano and Deepto Chakrabarty and Andrew Fabian and Jon Miller and Peter Bult and Zaven Arzoumanian and Steiner, {James F.} and Tod Strohmayer and Francesco Tombesi and Jeroen Homan and Cackett, {Edward M.} and Alice Harding",

note = "Published in Nature astronomy on 13th December 2021",

year = "2021",

month = dec,

day = "8",

doi = "10.1038/s41550-021-01524-8",

language = "English",

journal = "Nature Astronomy",

issn = "2397-3366",

publisher = "Springer Nature ",

}

Pasham, DR, Ho, WCG, Alston, W, Remillard, R, Ng, M, Gendreau, K, Metzger, BD, Altamirano, D, Chakrabarty, D, Fabian, A, Miller, J, Bult, P, Arzoumanian, Z, Steiner, JF, Strohmayer, T, Tombesi, F, Homan, J, Cackett, EM & Harding, A 2021, 'Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow', Nature Astronomy. https://doi.org/10.1038/s41550-021-01524-8

TY - JOUR

T1 - Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow

AU - Pasham, Dheeraj R.

AU - Ho, Wynn C. G.

AU - Alston, William

AU - Remillard, Ronald

AU - Ng, Mason

AU - Gendreau, Keith

AU - Metzger, Brian D.

AU - Altamirano, Diego

AU - Chakrabarty, Deepto

AU - Fabian, Andrew

AU - Miller, Jon

AU - Bult, Peter

AU - Arzoumanian, Zaven

AU - Steiner, James F.

AU - Strohmayer, Tod

AU - Tombesi, Francesco

AU - Homan, Jeroen

AU - Cackett, Edward M.

AU - Harding, Alice

N1 - Published in Nature astronomy on 13th December 2021

PY - 2021/12/8

Y1 - 2021/12/8

N2 - 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$\sigma$ 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 suggests a highly persistent signal that lasts for a billion cycles. The high frequency (rapid timescale) of 224 Hz (4.4 ms) argues for a compact object in AT2018cow, which can be a neutron star or black hole with a mass less than 850 solar masses. If the QPO is the spin period of a neutron star, we can set limits on the star's magnetic field strength. Our work highlights a new way of using high time-resolution X-ray observations to study FBOTs.

AB - 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$\sigma$ 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 suggests a highly persistent signal that lasts for a billion cycles. The high frequency (rapid timescale) of 224 Hz (4.4 ms) argues for a compact object in AT2018cow, which can be a neutron star or black hole with a mass less than 850 solar masses. If the QPO is the spin period of a neutron star, we can set limits on the star's magnetic field strength. Our work highlights a new way of using high time-resolution X-ray observations to study FBOTs.

KW - astro-ph.HE

U2 - 10.1038/s41550-021-01524-8

DO - 10.1038/s41550-021-01524-8

M3 - Article

SN - 2397-3366

JO - Nature Astronomy

JF - Nature Astronomy

ER -

Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow

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