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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

GRB 241030A: A fallback-accreting magnetar description of the early X-ray emission

  • Nissim Fraija1
  • Simone Dichiara2
  • Antonio Galván1
  1. 1Instituto de Astronomía, Universidad Nacional Autónoma de México , Circuito Exterior, C.U., A. Postal 70-264, 04510 México City ,
  2. 2The Pennsylvania State University Department of Astronomy and Astrophysics, , 525 Davey Lab, University Park, PA 16802 ,
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Abstract

The bright, variable early X-ray emission of GRB 241030A at z = 1.411 motivates investigating continued central-engine activity before the smoother afterglow emerges. We model a possible underlying magnetar contribution to the unabsorbed 0.3–10 keV XRT flux over 80–430 s, evolving the spin under fallback-disk and electromagnetic torques. A descriptive estimate gives P0 ≃ 4.25 ms, B ≃ 3.04 × 1015 G and source-frame tfb ≃ 143 s, with exploratory temporal-block uncertainty ranges. The effective efficiency reaches its geometry-dependent ceiling of 81.2. At observer time 200 s, this realization has P* ≃ 4.82 ms and magnetospheric, corotation and light-cylinder radii rm ≃ 235 km, rco ≃ 48 km and rLC ≃ 230 km. It is on the ejector branch; light-cylinder entry near 255 s initiates negative propeller torque and steepens the decline. The smooth component declines throughout the fitted interval; additional variable emission contributes to the observed maximum near 180 s. A correlated-residual Bayesian analysis permits a fainter component and broader dynamical histories, with median P0 = 16.8 ms and central 68 per cent interval 2.76–286 ms. However, posterior predictive checks reveal that this statistical description typically underpredicts the observed flux level and variability, limiting its physical interpretation. Fallback-modified magnetar activity remains a possible descriptive scenario, but these analyses do not establish a unique underlying component or robust constraints on the initial spin and disk-interaction history. We also discuss Lense–Thirring precession and alternative mechanisms as possible origins of the early X-ray variability.

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Cite

BibTeXRIS
BibTeX
@article{fraija2026241030a,
  title = {{GRB 241030A: A fallback-accreting magnetar description of the early X-ray emission}},
  author = {Nissim Fraija and Simone Dichiara and Antonio Galván},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag2044},
  url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2044/9005620},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - GRB 241030A: A fallback-accreting magnetar description of the early X-ray emission
AU  - Nissim Fraija
AU  - Simone Dichiara
AU  - Antonio Galván
PY  - 2026
DA  - 2026/10/30
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag2044
UR  - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2044/9005620
AB  - The bright, variable early X-ray emission of GRB 241030A at z = 1.411 motivates investigating continued central-engine activity before the smoother afterglow emerges. We model a possible underlying magnetar contribution to the unabsorbed 0.3–10 keV XRT flux over 80–430 s, evolving the spin under fallback-disk and electromagnetic torques. A descriptive estimate gives P0 ≃ 4.25 ms, B ≃ 3.04 × 1015 G and source-frame tfb ≃ 143 s, with exploratory temporal-block uncertainty ranges. The effective efficiency reaches its geometry-dependent ceiling of 81.2. At observer time 200 s, this realization has P* ≃ 4.82 ms and magnetospheric, corotation and light-cylinder radii rm ≃ 235 km, rco ≃ 48 km and rLC ≃ 230 km. It is on the ejector branch; light-cylinder entry near 255 s initiates negative propeller torque and steepens the decline. The smooth component declines throughout the fitted interval; additional variable emission contributes to the observed maximum near 180 s. A correlated-residual Bayesian analysis permits a fainter component and broader dynamical histories, with median P0 = 16.8 ms and central 68 per cent interval 2.76–286 ms. However, posterior predictive checks reveal that this statistical description typically underpredicts the observed flux level and variability, limiting its physical interpretation. Fallback-modified magnetar activity remains a possible descriptive scenario, but these analyses do not establish a unique underlying component or robust constraints on the initial spin and disk-interaction history. We also discuss Lense–Thirring precession and alternative mechanisms as possible origins of the early X-ray variability.
SN  - 0035-8711
SN  - 1365-2966
ER  -