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.

arXiv commentPublished in Nature astronomy on 13th December 2021

References in corpus (45)

• The Swift X-ray Telescope
• ATLAS: A High-Cadence All-Sky Survey System
• On characterising the variability properties of X-ray light curves from active galaxies
• Supernova Light Curves Powered by Young Magnetars
• Optimal binning of X-ray spectra and response matrix design
• Fourier Techniques for Very Long Astrophysical Time Series Analysis
• Rapidly-Evolving and Luminous Transients from Pan-STARRS1
• Optical and X-ray emission from stable millisecond magnetars formed from the merger of binary neutron stars
• An embedded X-ray source shines through the aspherical AT2018cow: revealing the inner workings of the most luminous fast-evolving optical transients
• Supernova Light Curves Powered by Fallback Accretion
• On Young Neutron Stars as Propellers and Accretors with Conventional Magnetic Fields
• The Cow: discovery of a luminous, hot and rapidly evolving transient
• The Fast, Luminous Ultraviolet Transient AT2018cow: Extreme Supernova, or Disruption of a Star by an Intermediate-Mass Black Hole?
• An Empirical Background Model for the NICER X-ray Timing Instrument
• Rapidly evolving transients in the Dark Energy Survey
• AT2018cow: a luminous millimeter transient
• The Koala: A Fast Blue Optical Transient with Luminous Radio Emission from a Starburst Dwarf Galaxy at $z=0.27$
• Effects of Fall-Back Accretion on Proto-Magnetar Outflows in Gamma-Ray Bursts and Superluminous Supernovae
• A mildly relativistic outflow from the energetic, fast-rising blue optical transient CSS161010 in a dwarf galaxy
• Supernova Fallback onto Magnetars and Propeller-Powered Supernovae
• Torque Enhancement, Spin Equilibrium, and Jet Power from Disk-Induced Opening of Pulsar Magnetic Fields
• A 200-s Quasi-Periodicity Following the Tidal Disruption of a Star by a Dormant Black Hole
• Black Hole Accretion Discs and Luminous Transients in Failed Supernovae from Non-Rotating Supergiants
• Swift spectra of AT2018cow: A White Dwarf Tidal Disruption Event?
• A Fourier Domain "Jerk" Search for Binary Pulsars
• Neutron star oscillations and QPOs during magnetar flares
• Observational properties of extreme supernovae
• Rapidly Rising Transients from Subaru Hyper Suprime-Cam Transient Survey
• The Core Collapse Supernova Rate from the SDSS-II Supernova Survey
• A Remarkably Loud Quasi-Periodicity after a Star is Disrupted by a Massive Black Hole
• Discovery of a ~2 hr high frequency X-ray QPO and iron K alpha reverberation in the active galaxy MS 2254.9-3712
• Swift 1644+57: The Longest Gamma-ray Burst?
• X-ray Swift observations of SN 2018cow
• A ~3.8 hour Periodicity from an Ultrasoft Active Galactic Nucleus Candidate
• Signatures of Circumstellar Interaction in the Unusual Transient AT2018cow
• From core collapse to superluminous: The rates of massive stellar explosions from the Palomar Transient Factory
• A Model for Fast Blue Optical Transient AT2018Cow: Circumstellar Interaction of a Pulsational Pair-instability Supernova
• FBOTs and AT2018cow following electron-capture collapse of merged white dwarfs
• Fast Optical Transients from Stellar-Mass Black Hole Tidal Disruption Events in Young Star Clusters
• Tidal Disruption of a Main-Sequence Star by an Intermediate-Mass Black Hole: A Bright Decade
• On the detectability of eccentric binary pulsars
• The nearby luminous transient AT2018cow: a magnetar formed in a sub-relativistically expanding non-jetted explosion
• ALMA Polarimetry of AT2018cow
• Searching for energy-resolved quasi-periodic oscillations in AGN
• The amplitude of the kilohertz quasi-periodic oscillations in 4U 1636$-$53 in the frequency-energy space

Cited by in corpus (29)

• Science objectives of the Einstein Probe mission
• The Birth of a Relativistic Jet Following the Disruption of a Star by a Cosmological Black Hole
• Live to die another day: the rebrightening of AT2018fyk as a repeating partial tidal disruption event
• X-ray eruptions every 22 days from the nucleus of a nearby galaxy
• Shocked jets in CCSNe can power the zoo of fast blue optical transients
• From X-rays to physical parameters: a comprehensive analysis of thermal tidal disruption event X-ray spectra
• Lense-Thirring Precession after a Supermassive Black Hole Disrupts a Star
• A Case for a Binary Black Hole System Revealed via Quasi-Periodic Outflows
• Minutes-duration Optical Flares with Supernova Luminosities
• An environmental analysis of the fast transient AT2018cow and implications for its progenitor and late-time brightness
• Dust Echoes from Luminous Fast Blue Optical Transients
• Late-time Hubble Space Telescope Observations of AT 2018cow. II. Evolution of a UV bright Underlying Source 2--4 Yr Post-discovery
• A flash of polarized optical light points to an aspherical "cow"
• A possible 250-second X-ray quasi-periodicity in the fast blue optical transient AT2018cow
• MUSSES2020J: The Earliest Discovery of a Fast Blue Ultraluminous Transient at Redshift 1.063
• On the nature of Fast Blue Optical Transients
• Neutrino Emission from Luminous Fast Blue Optical Transients
• Multi-wavelength observations of the Luminous Fast Blue Optical Transient AT2023fhn
• Late-time Hubble Space Telescope Observations of AT 2018cow. I. Further Constraints on the Fading Prompt Emission and Thermal Properties 50--60 Days Post-discovery
• AT2018fyk: Candidate Tidal Disruption Event by a (Super)massive Black Hole Binary
• An 85-s X-ray quasi-periodicity after a stellar tidal disruption by a candidate intermediate-mass black hole
• Prospects for Time-Domain and Multi-Messenger Science with eXTP
• Terminating a common envelope jets supernova impostor event with a super-Eddington blue supergiant
• The Black Hole Candidate Swift J1728.9$-$3613 and the Supernova Remnant G351.9$-$0.9
• The spectra of a radiative reprocessing outflow model for fast blue optical transients
• Luminous Fast Blue Optical Transients as "Failed" Gravitational-wave Sources: Helium Core$-$Black Hole Mergers Following Delayed Dynamical Instability
• The X-ray and Radio Loud Fast Blue Optical Transient AT2020mrf: Implications for an Emerging Class of Engine-Driven Massive Star Explosions
• Luminous Fast Blue Optical Transients and Type Ibn/Icn SNe from Wolf-Rayet/Black Hole Mergers
• AT2019ijn: a fast-rising, slow-decaying blue optical transient with exceptionally bright radio emission