AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events
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2026
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| author | 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 R. 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 |
| author_facet | 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 R. 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 |
| contents | We study AT2024kmq and AT2024lhc, two tidal disruption events (TDEs) with blue featureless spectra associated with high-mass black holes ($M_{\rm BH}\sim 10^8\,M_\odot$). 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 timescales of 1.3\,hr and 4.8\,hr for factor of $\sim3$ flux changes), long-lasting ($>1\,\rm yr$), emerging no later than the optical peak, and well characterized by power-laws with $1.7<Γ<3$ (where $f_ν\propto ν^{1-Γ}$). 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 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 $M_{\rm BH}$ distributions in TDEs with different X-ray spectral evolution properties: low-mass black holes ($M_{\rm BH} \sim 10^6 M_\odot$) remain soft ($Γ>4$) 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 ($1.5<Γ\lesssim 3$) 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 timescale predicted by simple disk theory scales with black hole mass as $t_{\rm tr}\propto M_{\rm BH}^{-3/4}$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_21624 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events 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 R. 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 High Energy Astrophysical Phenomena We study AT2024kmq and AT2024lhc, two tidal disruption events (TDEs) with blue featureless spectra associated with high-mass black holes ($M_{\rm BH}\sim 10^8\,M_\odot$). 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 timescales of 1.3\,hr and 4.8\,hr for factor of $\sim3$ flux changes), long-lasting ($>1\,\rm yr$), emerging no later than the optical peak, and well characterized by power-laws with $1.7<Γ<3$ (where $f_ν\propto ν^{1-Γ}$). 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 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 $M_{\rm BH}$ distributions in TDEs with different X-ray spectral evolution properties: low-mass black holes ($M_{\rm BH} \sim 10^6 M_\odot$) remain soft ($Γ>4$) 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 ($1.5<Γ\lesssim 3$) 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 timescale predicted by simple disk theory scales with black hole mass as $t_{\rm tr}\propto M_{\rm BH}^{-3/4}$. |
| title | AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2602.21624 |