Article

AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events

Yuhan YaoBerkeley Center for Multi-messenger Research on Astrophysical Transients and Outreach (Multi-RAPTOR), University of California , Berkeley, CA 94720-3411 ,R. ChornockBerkeley Center for Multi-messenger Research on Astrophysical Transients and Outreach (Multi-RAPTOR), University of California , Berkeley, CA 94720-3411 ,Andrew MummerySchool of Natural Sciences, Institute for Advanced Study , 1 Einstein Drive, Princeton, NJ 08540 ,Raffaella MarguttiBerkeley Center for Multi-messenger Research on Astrophysical Transients and Outreach (Multi-RAPTOR), University of California , Berkeley, CA 94720-3411 ,Marat GilfanovMax-Planck-Institut für Astrophysik , Karl-Schwarzschild-Str 1, D-85741 Garching ,Muryel GuoloBloomberg Center for Physics and Astronomy, Johns Hopkins University , 3400 N. Charles St., Baltimore, MD 21218 ,Eric R CoughlinDepartment of Physics, Syracuse University , Syracuse, NY 13210 ,Wenbin LuBerkeley Center for Multi-messenger Research on Astrophysical Transients and Outreach (Multi-RAPTOR), University of California , Berkeley, CA 94720-3411 ,Joheen ChakrabortyDepartment of Physics & Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology , Cambridge, MA 02139 ,Dheeraj R. PashamDepartment of Physics, The George Washington University , Washington, DC 20052 ,Kate D AlexanderDepartment of Astronomy/Steward Observatory , 933 North Cherry Avenue, Room N204, Tucson, AZ 85721-0065 ,Olivia AspegrenDepartment of Astronomy, University of California , Berkeley, CA 94720-3411 ,C. R. AngusAstrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast , Belfast BT7 1NN ,Xinze GuoBerkeley Center for Multi-messenger Research on Astrophysical Transients and Outreach (Multi-RAPTOR), University of California , Berkeley, CA 94720-3411 ,Xander J. HallMcWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, PA 15213 ,Erica HammersteinBerkeley Center for Multi-messenger Research on Astrophysical Transients and Outreach (Multi-RAPTOR), University of California , Berkeley, CA 94720-3411 ,K-Ryan HindsAstrophysics Research Institute, Liverpool John Moores University , 146 Brownlow Hill, Liverpool L3 5RF ,A. HoDepartment of Astronomy, Cornell University , Ithaca, NY 14853 ,Xiaoshan HuangCalifornia Institute of Technology , TAPIR, Mail Code 350-17, Pasadena, CA 91125 ,Elias KammounDivision of Physics, Mathematics and Astronomy, California Institute of Technology , 1200 E. California Blvd, Pasadena, CA 91125 ,Natalie LeBaronBerkeley Center for Multi-messenger Research on Astrophysical Transients and Outreach (Multi-RAPTOR), University of California , Berkeley, CA 94720-3411 ,Matteo LucchiniAnton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, NL-1098XH Amsterdam ,Zoë McGrathAstrophysics Research Institute, Liverpool John Moores University , 146 Brownlow Hill, Liverpool L3 5RF ,M NichollAstrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast , Belfast BT7 1NN ,D. A. PerleyAstrophysics Research Institute, Liverpool John Moores University , 146 Brownlow Hill, Liverpool L3 5RF ,R Michael RichDepartment of Physics and Astronomy, University of California , Los Angeles, CA 90095 ,Genevieve SchroederDepartment of Astronomy, Cornell University , Ithaca, NY 14853 ,Xinyue ShengAstrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast , Belfast BT7 1NN ,J. SollermanThe Oskar Klein Centre, Department of Astronomy, Stockholm University , AlbaNova, SE-10691, Stockholm ,Jean SomalwarBerkeley Center for Multi-messenger Research on Astrophysical Transients and Outreach (Multi-RAPTOR), University of California , Berkeley, CA 94720-3411 ,J. WiseAstrophysics Research Institute, Liverpool John Moores University , 146 Brownlow Hill, Liverpool L3 5RF ,M. W. CoughlinSchool of Physics and Astronomy, University of Minnesota , Minneapolis, Minnesota 55455 ,Andrew DrakeCahill Center for Astrophysics, California Institute of Technology , MC 249-17, 1200 E California Boulevard, Pasadena, CA 91125 ,M. J. GrahamCahill Center for Astrophysics, California Institute of Technology , MC 249-17, 1200 E California Boulevard, Pasadena, CA 91125 ,George HelouInfrared Processing and Analysis CenterJoahan Castaneda JaimesDivision of Physics, Mathematics and Astronomy, California Institute of Technology , 1200 E. California Blvd, Pasadena, CA 91125 ,M. M. KasliwalCahill Center for Astrophysics, California Institute of Technology , MC 249-17, 1200 E California Boulevard, Pasadena, CA 91125 ,Ashish A MahabalCenter for Data Driven Discovery, California Institute of Technology , Pasadena, CA 91125 ,Pavel MedvedevSpace Research Institute (IKI), Russian Academy of Sciences , Profsoyuznaya 84/32, Moscow 117997 ,Josiah PurdumCaltech Optical Observatories, California Institute of Technology , Pasadena, CA 91125 ,Ben RusholmeIPAC, California Institute of Technology , 1200 E. California Blvd, Pasadena, CA 91125 ,Rashid SunyaevMax-Planck-Institut für Astrophysik , Karl-Schwarzschild-Str 1, D-85741 Garching ,

Monthly Notices of the Royal Astronomical Societyjournal2026en

ABI

Abstract

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

Topics

Astrophysical Phenomena and Observations Pulsars and Gravitational Waves Research Astrophysics and Cosmic Phenomena

Identifiers

DOI: 10.1093/mnras/stag920

Citations and references

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