June
2026
•
2026MNRAS.549ag920Y
Authors
•
Yao, Yuhan
•
Chornock, Ryan
•
Mummery, Andrew
•
Margutti, Raffaella
•
Gilfanov, Marat
•
Guolo, Muryel
•
Coughlin, Eric R.
•
Lu, Wenbin
•
Chakraborty, Joheen
•
Pasham, Dheeraj R.
•
Alexander, Kate D.
•
Aspegren, Olivia
•
Angus, Charlotte R.
•
Guo, Xinze
•
Hall, Xander J.
•
Hammerstein, Erica
•
Hinds, K.-Ryan
•
Ho, Anna Y. Q.
•
Huang, Xiaoshan
•
Kammoun, Elias
•
LeBaron, Natalie
•
Lucchini, Matteo
•
McGrath, Zoë
•
Nicholl, Matt
•
Perley, Daniel A.
•
Rich, R. Michael
•
Schroeder, Genevieve
•
Sheng, Xinyue
•
Sollerman, Jesper
•
Somalwar, Jean
•
Wise, Jacob L.
•
Coughlin, Michael W.
•
Drake, Andrew
•
Graham, Matthew J.
•
Helou, George
•
Jaimes, Joahan C.
•
Kasliwal, Mansi M.
•
Mahabal, Ashish A.
•
Medvedev, Pavel
•
Purdum, Josiah
•
Rusholme, Ben
•
Sunyaev, Rashid
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 (>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 $t_{\rm tr}\propto M_{\rm BH}^{-3/4}$.
Links
