Revisiting the Multiwavelength Data of GRB 240825A: Implications for a Two-Stage Central Engine and a Dusty Environment
Abstract
Reanalyzing the multi-wavelength data of GRB 240825A, we identify two distinct prompt-emission episodes, i.e. an early, spectrally soft plateau and a subsequent bright, spectrally hard gamma-ray pulse. We show that this signature is consistent with a two-stage central engine model, in which the early soft plateau is powered by the dipolar spin-down radiation of a transient proto-magnetar, while the later hard pulse arises from a relativistic jet launched by fallback accretion onto the nascent black hole via the Blandford-Znajek mechanism. Adopting simulation-motivated initial black hole (BH) masses (MBH,0) and spins (a0), our fits to the second episode yield total masses supplied to the post-collapse disk of Mfb=0.45--0.96 M⊙, fallback radii of rfb=16.9--17.6 rg, and characteristic fallback timescales of tfb=0.13--$0.25$ s. The corresponding maximum inner accretion rates range from $0.18$ to 0.70 M⊙ s−1, which is sensitive to a0. Joint spectral fits with optical-X-ray afterglow data reveal a coupled temporal evolution of dust extinction and equivalent hydrogen column density. Incorporating this extinction evolution, an external forward-reverse shock model in a wind-like medium can account for the radio-to-GeV band afterglow data. Although ambient dust and the bright host galaxy may obscure any associated supernova, late-time optical reddening remains compatible with a supernova contribution. Applying the empirical relation between the prompt spectral peak energy and the SN peak bolometric magnitude gives an illustrative estimate of Mbol,peak=−19.46±0.35 mag for a putative associated SN. These results support a two-stage evolution of the central engine and variable dusty environment of GRB 240825A, which provides insights into the nature of its progenitor.
Related
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BibTeX
@misc{xiong2026revisiting,
title = {{Revisiting the Multiwavelength Data of GRB 240825A: Implications for a Two-Stage Central Engine and a Dusty Environment}},
author = {Ren-Jie Xiong and Zi-Qi Wang and Xiao-Li Huang and En-Wei Liang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.15703},
eprint = {2610.15703},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.15703},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Revisiting the Multiwavelength Data of GRB 240825A: Implications for a Two-Stage Central Engine and a Dusty Environment
AU - Ren-Jie Xiong
AU - Zi-Qi Wang
AU - Xiao-Li Huang
AU - En-Wei Liang
PY - 2026
DA - 2026/10/11
PB - arXiv
DO - 10.48550/arxiv.2610.15703
UR - https://arxiv.org/abs/2610.15703
AB - Reanalyzing the multi-wavelength data of GRB 240825A, we identify two distinct prompt-emission episodes, i.e. an early, spectrally soft plateau and a subsequent bright, spectrally hard gamma-ray pulse. We show that this signature is consistent with a two-stage central engine model, in which the early soft plateau is powered by the dipolar spin-down radiation of a transient proto-magnetar, while the later hard pulse arises from a relativistic jet launched by fallback accretion onto the nascent black hole via the Blandford-Znajek mechanism. Adopting simulation-motivated initial black hole (BH) masses (M_BH,0) and spins (a_0), our fits to the second episode yield total masses supplied to the post-collapse disk of M_fb=0.45--0.96 M_⊙, fallback radii of r_fb=16.9--17.6 r_g, and characteristic fallback timescales of t_fb=0.13--$0.25$ s. The corresponding maximum inner accretion rates range from $0.18$ to 0.70 M_⊙ s^−1, which is sensitive to a_0. Joint spectral fits with optical-X-ray afterglow data reveal a coupled temporal evolution of dust extinction and equivalent hydrogen column density. Incorporating this extinction evolution, an external forward-reverse shock model in a wind-like medium can account for the radio-to-GeV band afterglow data. Although ambient dust and the bright host galaxy may obscure any associated supernova, late-time optical reddening remains compatible with a supernova contribution. Applying the empirical relation between the prompt spectral peak energy and the SN peak bolometric magnitude gives an illustrative estimate of M_bol,peak=−19.46±0.35 mag for a putative associated SN. These results support a two-stage evolution of the central engine and variable dusty environment of GRB 240825A, which provides insights into the nature of its progenitor.
ER -