EP241021a: a months-duration X-ray transient with luminous optical and radio emission

Abstract

We present the discovery of a peculiar X-ray transient, EP241021a, by the Einstein Probe (EP) mission, and the results from multiwavelength follow-up observations. The transient was first detected with the Wide-field X-ray Telescope as an intense flare lasting for ~100 s, reaching a luminosity of L_(0.5-4 keV)~10^48 erg/s at z=0.748. Further observations with EP's Follow-up X-ray Telescope reveal a huge drop in the X-ray flux by a factor of >1000 within 1.5 days. After maintaining a nearly plateau phase for ~7 days, the X-ray flux declines as t^-1.2 over a period of ~30 days, followed by a sudden decrease to an undetectable level by EP and XMM-Newton, making it the longest afterglow emission detected among known fast X-ray transients. A bright counterpart at optical and radio wavelengths was also detected, with high peak luminosities in excess of 10^44 erg/s and 10^41 erg/s, respectively. In addition, EP241021a exhibits a non-thermal X-ray spectrum, red optical color, X-ray and optical rebrightenings in the light curves, and fast radio spectral evolution, suggesting that relativistic jets may have been launched. We discuss possible origins of EP241021a, including a choked jet with supernova shock breakout, a merger-triggered magnetar, a highly structured jet, and a repeating partial tidal disruption event involving an intermediate-mass black hole, but none can perfectly explain the multiwavelength properties. EP241021a may represent a new type of X-ray transients with months-duration evolution timescales, and future EP detections and follow-up observations of similar systems will provide statistical samples to understand the underlying mechanisms at work.

References in corpus (73)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• Star Formation in Galaxies Along the Hubble Sequence
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The Host Galaxies and Classification of Active Galactic Nuclei
• X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue
• The shock break-out of GRB 060218/SN 2006aj
• The Shape of Spectral Breaks in GRB Afterglows
• A `Hypernova' model for SN 1998bw associated with gamma-ray burst of 25 April 1998
• Opacities and Spectra of the r-process Ejecta from Neutron Star Mergers
• Hydrodynamical Simulations to Determine the Feeding Rate of Black Holes by the Tidal Disruption of Stars: The Importance of the Impact Parameter and Stellar Structure
• DiFX2: A more flexible, efficient, robust and powerful software correlator
• An extremely luminous X-ray outburst at the birth of a supernova
• Afterglow lightcurves, viewing angle and the jet structure of gamma-ray bursts
• Swift J2058.4+0516: Discovery of a Possible Second Relativistic Tidal Disruption Flare?
• Off-Axis Afterglow Emission from Jetted Gamma-Ray Bursts
• Refreshed Shocks and Afterglow Longevity in GRB
• A unified model for tidal disruption events
• Gamma-ray burst beaming: a universal configuration with a standard energy reservoir?
• An optimized algorithm for multi-scale wideband deconvolution of radio astronomical images
• Optical and X-ray emission from stable millisecond magnetars formed from the merger of binary neutron stars
• Overall Evolution of Jetted Gamma-ray Burst Ejecta
• Bright "merger-nova" from the remnant of a neutron star binary merger: A signature of a newly born, massive, millisecond magnetar
• Fully-Automated Reduction of Longslit Spectroscopy with the Low Resolution Imaging Spectrometer at Keck Observatory
• Discovery of an outflow from radio observations of the tidal disruption event ASASSN-14li
• Early X-ray and optical afterglow of gravitational wave bursts from mergers of binary neutron stars
• Swift J1644+57 gone MAD: the case for dynamically-important magnetic flux threading the black hole in a jetted tidal disruption event
• Finite, Intense Accretion Bursts from Tidal Disruption of Stars on Bound Orbits
• Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. I. Jet Energetics and the Pristine Parsec-Scale Environment of a Supermassive Black Hole
• The Konus-Wind catalog of gamma-ray bursts with known redshifts. I. Bursts detected in the triggered mode
• A very luminous jet from the disruption of a star by a massive black hole
• Evolution of Accretion Disks in Tidal Disruption Events
• First Results from MASIV: The Micro-Arcsecond Scintillation-Induced Variability Survey
• A retrospective view of Miriad
• Nested Sampling Methods
• Swift J1644+57: A White Dwarf Tidally Disrupted by a 10^4 M_{odot} Black Hole?
• A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients
• Radius constraints and minimal equipartition energy of relativistically moving synchrotron sources
• Discovery of a new kind of explosive X-ray transient near M86
• A New, Faint Population of X-ray Transients
• Science objectives of the Einstein Probe mission
• Analyzing the Largest Spectroscopic Dataset of Hydrogen-Poor Super-Luminous Supernovae
• Peak Energy-Isotropic Energy Relation in the Off-Axis Gamma-Ray Burst Model
• GRRMHD Simulations of Tidal Disruption Event Accretion Disks around Supermassive Black Holes: Jet Formation, Spectra, and Detectability
• The Birth of a Relativistic Jet Following the Disruption of a Star by a Cosmological Black Hole
• Radio Observations of an Ordinary Outflow from the Tidal Disruption Event AT2019dsg
• X-ray counterpart of gravitational waves due to binary neutron star mergers: light curves, luminosity functions, and event rate densities
• The Automated Photometry Of Transients (AutoPhOT) pipeline
• A new three-parameter correlation for gamma-ray bursts with a plateau phase in the afterglow
• Extragalactic fast X-ray transient candidates discovered by Chandra (2000-2014)
• Two fast X-ray transients in archival Chandra data
• Blasts from the Past: Supernova Shock Breakouts among X-Ray Transients in the XMM-Newton Archive
• Extragalactic FXT Candidates Discovered by Chandra (2014-2022)
• The Definitive X-ray Light Curve of Swift J164449.3+573451
• Optical to X-ray Signatures of Dense Circumstellar Interaction in Core-Collapse Supernovae
• On the origin of the radio emission of Sw 1644+57
• Triggering the Untriggered: The First Einstein Probe-Detected Gamma-Ray Burst 240219A and Its Implications
• Discovery of Three Candidate Magnetar-powered Fast X-ray Transients from Chandra Archival Data
• X-ray transients from the accretion-induced collapse of white dwarfs
• Fast, ultra-luminous X-ray bursts from tidal stripping of White Dwarfs by Intermediate-mass Black Holes
• Observational Signatures of High-Energy Emission during the Shallow Decay Phase of GRB X-Ray Afterglows
• The RapidXMM Upper Limit Server: X-ray aperture photometry of the XMM-Newton archival observations
• Pseudo Redshifts of Gamma-Ray Bursts Derived from the L-T-E Correlation
• Optical and radio transients after the collapse of super-Chandrasekhar white dwarf merger remnants
• CDF-S XT1 and XT2: White Dwarf Tidal Disruption Events by Intermediate-Mass Black Holes?
• An analytic derivation of the empirical correlations of gamma-ray bursts
• Einstein Probe discovery of EP240408a: a peculiar X-ray transient with an intermediate timescale
• The Fast X-ray Transient XRT 210423 and its Host Galaxy
• Classifying Intermediate Redshift Galaxies in SDSS: Alternative Diagnostic Diagrams
• Late-time X-ray Observations of the Jetted Tidal Disruption Event AT2022cmc: The Relativistic Jet Shuts Off
• Possible origin of AT2021any: a failed GRB from a structured jet
• Fate of the remnant in tidal stripping event: repeating and non-repeating

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