Early Infrared Excess and the Birth of a Corona in Tidal Disruption Event 2024aepd ✛ ✦
Context
When a star gets too close to a supermassive black hole, the law of universal gravitation produces tidal forces that tear it apart. Such tidal disruption events (TDEs) allow us to observe, over mere months, processes that in active galactic nuclei span millions of years. Understanding the evolution of accretion disks and the formation of coronae around black holes is one of the key goals of modern astrophysics.
Methods
A global network of telescopes tracked the event from radio to X-ray wavelengths. Key data were obtained using photometry and spectroscopy with instruments like ZTF, ATLAS, NOTCam, EMIR, and Swift. The distance to the galaxy was determined thanks to the redshift discovered by Edwin Hubble. Spectral analysis included model fitting based on Planck's law and the Compton effect to disentangle the contributions of various components.
Results
Already by ~40 days, a dust infrared excess emerged, but its spectrum is better explained by free-free emission in a plasma envelope that reprocesses hard radiation. In parallel, the X-ray spectrum underwent a dramatic transformation: around 178 days, the thermal disk emission gave way to a non-thermal power law with an index of Γ≈1.8, interpreted as the birth of a hot corona, where photons hardened by Compton scattering soar to high energies. The similarity to the low/hard state in X-ray binaries points to a universal mechanism.
Implications
The observed transition strengthens the idea that tidal disruption events are ideal proving grounds for studying accretion physics. The fact that the photon index rises with luminosity without a subsequent break challenges models developed for active galactic nuclei and binary systems, and calls for a revision of accretion disk evolution scenarios.
Future development
Future surveys, such as LSST at the Vera Rubin Observatory, will detect thousands of such events. Coordinated infrared and X-ray campaigns will help clarify whether the early excess is a universal feature and how the plasma in the corona evolves over time. As far back as the 1970s, Rashid Sunyaev laid the foundations of accretion disk theory, anticipating studies like this one.
Impact
The results will have a direct impact on accretion theory, modeling of tidal disruption events, and the interpretation of observations of intermediate-mass black holes.
Next steps
It is critically important to gather statistics on the early infrared excess and, simultaneously, to conduct detailed numerical simulations of reprocessing envelopes that account for Comptonization and free-free processes.
Key open problems
The study is directly connected to the puzzles of corona formation and evolution, the geometry of the accretion flow, and the role the environment—including cosmic dust—plays in reprocessing radiation.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This work presents multiwavelength observations of TDE 2024aepd over ~300 days. The X-ray spectrum showed a transition from thermal disk emission to a power law, interpreted as the birth of a hot corona. An early infrared excess at ~day 40 with a nearly flat spectrum points to free-free emission from a plasma shell, rather than a dust echo.
Where its strength is
We detected rapid evolution of the accretion flow: corona formation and an early infrared signature not explainable by a standard dust echo. This offers a rare opportunity to witness the birth of a corona in real time.
Where it could go next
- It might be interesting to compare the observed spectral transformation with accretion models at super-Eddington rates, which are discussed in the context of little red dots—perhaps the corona formation mechanism is universal.based on: Cosmic Pressure Cooker: Unraveling the Mystery of Little Red Dots arXiv:2607.17448v1
- The early infrared excess can be compared with dust echoes in active galactic nuclei to clarify the contribution of free-free emission and reprocessing of hard radiation in the shell.based on: A Dusty Flare at the Heart of a Galaxy arXiv:2605.29616
Worth trying
- Test whether the power-law X-ray spectrum can be described by Comptonization in a corona of variable optical depth, analogous to states of X-ray binaries.
- Assess whether the infrared excess can be reproduced by emission from an expanding shell reprocessing X-ray radiation from the corona, without invoking dust.
- Search for a delay between X-ray and infrared variations to diagnose the geometry of the reprocessing region.
Why this may matter
The rapid spectral state change in this TDE allows us to test accretion models on scales inaccessible in steady systems and may serve as a key to understanding corona formation around supermassive black holes.
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The closest work in the archive sits at 0.64 by meaning — the usual level for our corpus.
Original abstract
as written by the authors arXiv:2607.14696
We present multi-wavelength observations of the tidal disruption event (TDE) 2024aepd, spanning primarily the first $$\sim$$300 days after discovery. The X-ray spectrum is initially dominated by a thermal disk component accompanied by a hard excess. From $$\sim$$178 days onward, the spectrum becomes power-law dominated and subsequently hardens, indicating the rapid emergence and strengthening of a hot corona. A prominent near-infrared (NIR) excess is detected as early as $$\sim40$$ days. Its nearly flat power-law spectrum strongly deviates from the Rayleigh-Jeans tail of the UV-optical blackbody. Although a conventional dust-echo origin cannot be completely ruled out, free-free emission from a reprocessing photospheric envelope provides a more plausible explanation. Moreover, the UV-optical-to-NIR break shifts to higher frequencies as the density-profile index remains nearly constant, implying evolving reprocessing conditions within a broadly unchanged density structure. Together with AT2019azh and TDE 2025abcr, TDE 2024aepd is the third TDE reported to exhibit an early-time NIR excess. A larger sample with early-time NIR coverage is needed to determine whether such excesses are common among TDEs.
For a supermassive black hole of a million solar masses to tear apart a Sun-like star, the star must approach within a distance comparable to the orbit of Mercury — otherwise the tidal forces are insufficient.
Key numbers
- Peak ultraviolet luminosity: 1.3×1044 erg/s
- Black hole mass: ~2.7×106 M☉
- Transition time to the hard X-ray state: ~178 days after discovery
- Peak bolometric luminosity: ~1.4×1045 erg/s
- Infrared spectral index: ≈ 0.2