AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events

Yao, Y, Chornock, R, Mummery, A, Margutti, R, Gilfanov, M, Guolo, M, Coughlin, ER, Lu, W, Chakraborty, J, Pasham, DR, Alexander, KD, Aspegren, O, Angus, CR, Guo, X, Hall, XJ, Hammerstein, E, Hinds, K-R, Ho, AYQ, Huang, X, Kammoun, E et al (2026) AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events. Monthly Notices of the Royal Astronomical Society, 549 (2). ISSN 0035-8711

Preview

Text AT2024lhc and AT2024kmq in the landscape of featureless tidal disruption events.pdf - Published Version Available under License Creative Commons Attribution. Download (8MB) | Preview

Abstract

We study AT2024kmq and AT2024lhc, two tidal disruption events (TDEs) with blue featureless spectra associated with high-mass black holes ( MBH ∼ 108 M⊙). Both events show optical precursors consistent with shock dissipation from stream self-intersection. Their X-ray emission is luminous ( LX ∼ 1044 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 < < 3 (where fν ∝ ν1 − ). The X-ray properties and radio non-detections support a compact corona ( ≲ 10 rg ) 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 MBH distributions in TDEs with different X-ray spectral evolution properties: low-mass black holes ( MBH ∼ 106 M⊙) remain soft ( > 4 ) within t ≲ 2 yr, intermediate masses ( ∼ 107 M⊙) transition from soft to hard at ∼1 yr, while high masses ( ∼ 108 M⊙) are hard ( 1 . 5 < ≲ 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 ˙Macc ∼ 0 . 03 ˙MEdd (similar to X-ray binaries), using the fact that the transition time-scale predicted by simple disc theory scales with black hole mass as ttr ∝ M−3 / 4 BH

Item Type:	Article
Uncontrolled Keywords:	astro-ph.HE; astro-ph.HE; 5101 Astronomical Sciences; 51 Physical Sciences; 7 Affordable and Clean Energy; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	11 May 2026
Date of first compliant Open Access:	10 June 2026
Date Deposited:	10 Jun 2026 13:00
Last Modified:	10 Jun 2026 13:00
DOI or ID number:	10.1093/mnras/stag920
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28800

View Item