AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events

Abstract

We study AT2024kmq and AT2024lhc, two tidal disruption events (TDEs) with blue featureless spectra associated with high-mass black holes ($M_{\mathrm{BH}}\sim 10^8{M}_{\odot }$). Both events show optical precursors consistent with shock dissipation from stream self-intersection. Their X-ray emission is luminous ($L_{\mathrm{X}}\sim 10^{44}\mathrm{erg}{\mathrm{s}}^{-1}$), highly variable (with minimum observed variability timescales of 1.3\,hr and 4.8\,hr for factor of $\sim 3$ flux changes), long-lasting ($>1\mathrm{yr}$), emerging no later than the optical peak, and well characterized by power-laws with $1.7<\Gamma <3$ (where $f_{\nu }\propto {\nu }^{1-\Gamma }$). The X-ray properties and radio non-detections support a compact corona ($\lesssim 10r_{\mathrm{g}}$) producing Comptonized X-ray emission. Using all published featureless TDEs, we find statistically significant bimodality in the distribution of their peak UV/optical blackbody luminosities and radii. We assemble a comparison TDE sample with early-time X-ray observations with eROSITA, in which we find different $M_{\mathrm{BH}}$ distributions in TDEs with different X-ray spectral evolution properties: low-mass black holes ($M_{\mathrm{BH}}\sim 10^6{M}_{\odot }$) remain soft ($\Gamma >4$) within $t\lesssim 2$\,yr, intermediate masses ($\sim 10^7{M}_{\odot }$) transition from soft to hard at $\sim$1 yr, while high masses ($\sim 10^8{M}_{\odot }$) are hard ($1.5<\Gamma \lesssim 3$) from the outset. We interpret this result as evidence that the soft-to-hard state transition in TDEs occurs at the critical threshold of ${\dot{M}}_{\mathrm{acc}}\sim 0.03{\dot{M}}_{\mathrm{Edd}}$ (similar to X-ray binaries), using the fact that the transition timescale predicted by simple disk theory scales with black hole mass as $t_{\mathrm{tr}}\propto M_{\mathrm{BH}}^{-3/4}$.

24 pages, 16 figures, submitted to MNRAS

References in corpus (67)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• X-ray Properties of Black-Hole Binaries
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• Modelling the behaviour of accretion flows in X-ray binaries
• The Co-Evolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• CASA, the Common Astronomy Software Applications for Radio Astronomy
• The eROSITA X-ray telescope on SRG
• The Zwicky Transient Facility: Science Objectives
• Stellar Population Inference with Prospector
• Accretion disc viscosity: how big is alpha?
• Overview of the Instrumentation for the Dark Energy Spectroscopic Instrument
• The SRG X-ray orbital observatory, its telescopes and first scientific results
• The unWISE Catalog: Two Billion Infrared Sources from Five Years of WISE Imaging
• Seventeen Tidal Disruption Events from the First Half of ZTF Survey Observations: Entering a New Era of Population Studies
• Design and operation of the ATLAS Transient Science Server
• The Zwicky Transient Facility: Observing System
• Full spectrum fitting with photometry in pPXF: stellar population versus dynamical masses, non-parametric star formation history and metallicity for 3200 LEGA-C galaxies at redshift z~0.8
• The Final Season Reimagined: 30 Tidal Disruption Events from the ZTF-I Survey
• Optical-Ultraviolet Tidal Disruption Events
• A very luminous jet from the disruption of a star by a massive black hole
• ASASSN-14ko is a Periodic Nuclear Transient in ESO 253-G003
• The Fundamental Plane of Black Hole Accretion and its Use as a Black Hole-Mass Estimator
• ZTF Early Observations of Type Ia Supernovae I: Properties of the 2018 Sample
• The spectral evolution of disc dominated tidal disruption events
• A data science platform to enable time-domain astronomy
• Fundamental scaling relationships revealed in the optical light curves of tidal disruption events
• A population of highly energetic transient events in the centres of active galaxies
• Rapid accretion state transitions following the tidal disruption event AT2018fyk
• The Curious Case of ASASSN-20hx: A Slowly-Evolving, UV and X-ray Luminous, Ambiguous Nuclear Transient
• The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflection, and Rapid Evolution of the Disk-Corona System
• Investigating state transition luminosities of Galactic black hole transients in the outburst decay
• Double tidal disruptions in galactic nuclei
• First light from tidal disruption events
• Fainter harder brighter softer: a correlation between ${\alpha }_{\mathrm{ox}}$ , X-ray spectral state and Eddington ratio in tidal disruption events
• AT 2019avd: A novel addition to the diverse population of nuclear transients
• Discovery of a Fast Iron Low-ionization Outflow in the Early Evolution of the Nearby Tidal Disruption Event AT2019qiz
• AT2019 avd: A tidal disruption event with a two-phase evolution
• The nuclear transient AT 2017gge: a tidal disruption event in a dusty and gas-rich environment and the awakening of a dormant SMBH
• The unluckiest star: A spectroscopically confirmed repeated partial tidal disruption event AT 2022dbl
• Swift J1644+57 as an off-axis Jet
• The bulge masses of TDE host galaxies and their scaling with black hole mass
• On the impact of relativistic gravity on the rate of tidal disruption events
• Limits on mass outflow from optical tidal disruption events
• Searching for Ultra-light Bosons and Constraining Black Hole Spin Distributions with Stellar Tidal Disruption Events
• The maximum mass of a black hole which can tidally disrupt a star: measuring black hole spins with tidal disruption events
• Synchrotron Afterglow Model for AT 2022cmc: Jetted Tidal Disruption Event or Engine-Powered Supernova?
• A Bright First Day for Tidal Disruption Event
• Tidal Disruption Events through the Lens of the Cooling Envelope Model
• Late-time X-ray Observations of the Jetted Tidal Disruption Event AT2022cmc: The Relativistic Jet Shuts Off
• Repeating Partial Tidal Encounters of Sun-like Stars Leading to their Complete Disruption
• An upper observable black hole mass scale for tidal disruption events with thermal X-ray spectra
• Hard X-ray emission from a Compton scattering corona in large black hole mass tidal disruption events
• A New Forced Photometry Service for the Zwicky Transient Facility
• A luminous X-ray transient in SDSS J143359.16+400636.0: a likely tidal disruption event
• Ultraviolet Spectral Evidence for Ansky as a Slowly Evolving Featureless Tidal Disruption Event with Quasiperiodic Eruptions
• Tidal disruption rate suppression by the event horizon of spinning black holes
• eROSITA-RU Tidal Disruption Events with Keck-I/LRIS: Sample Selection, Optical Properties, and Host Galaxy Demographics
• The Emission and Suppression of Line Features in Luminous Transients
• Tidal disruption event Calorimetry: Observational constraints on the physics of TDE optical flares
• AT2019cmw: A highly luminous, cooling featureless TDE candidate from the disruption of a high mass star in an early-type galaxy
• Compact Accretion Disks in the Aftermath of Tidal Disruption Events: Parameter Inference from Joint X-ray Spectra and UV/Optical Photometry Fitting
• How Flat is a Plateau? Evolution of Late-Time TDE Disks
• Disk-to-Corona State Transition and Extreme X-ray Variability in the Tidal Disruption Event AT2019teq
• X-ray Variability and Photosphere Evolution during Accretion Disk Formation in Tidal Disruption Events