The Radio Flare and Multiwavelength Afterglow of the Short GRB 231117A: Energy Injection from a Violent Shell Collision

Abstract We present the early radio detection and multiwavelength modeling of the short gamma-ray burst (GRB) 231117A at redshift z = 0.257. The Australia Telescope Compact Array automatically triggered a 9 hr observation of GRB 231117A at 5.5 and 9 GHz following its detection by the Neil Gehrels Swift Observatory just 1.3 hr post-burst. Splitting this observation into 1 hr time bins, the early radio afterglow exhibited flaring, scintillating and plateau phases. The scintillation allowed us to place the earliest upper limit (&lt;10 hr) on the size of a GRB blast wave to date, constraining it to &lt;1 × 10 16 cm. Multiwavelength modeling of the full afterglow required a period of significant energy injection between ∼0.02 and 1 day. The energy injection was modeled as a violent collision of two shells: a reverse shock passing through the injection shell explains the early radio plateau, while an X-ray flare is consistent with a shock passing through the leading impulsive shell. Beyond 1 day, the blast wave evolves as a classic decelerating forward shock with an electron distribution index of p = 1.66 ± 0.01. Our model also indicates a jet break at ∼2 days, and a half-opening angle of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>j</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>16</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> <mml:mn>6</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> <mml:mn>1</mml:mn> </mml:math> . Following the period of injection, the total energy is ζ ∼ 18 times the initial impulsive energy, with a final collimation-corrected energy of E Kf ∼ 5.7 × 10 49 erg. The minimum Lorentz factors this model requires are consistent with constraints from the early radio measurements of Γ &gt; 35 to Γ &gt; 5 between ∼0.1 and 1 day. These results demonstrate the importance of rapid and sensitive radio follow-up of GRBs for exploring their central engines and outflow behaviour.

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The Astrophysical Journal
Published
2025-11-11
DOI
https://doi.org/10.3847/1538-4357/adfed7
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Gamma-ray bursts and supernovae
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article

The Radio Flare and Multiwavelength Afterglow of the Short GRB 231117A: Energy Injection from a Violent Shell Collision

J. P. Anderson, E. A. Magnier, J. F. Agüí Fernández, F. Schüßler et al.
The Astrophysical Journal
Gamma-ray bursts and supernovae
article

The Radio Flare and Multiwavelength Afterglow of the Short GRB 231117A: Energy Injection from a Violent Shell Collision

J. P. Anderson, E. A. Magnier, J. F. Agüí Fernández, F. Schüßler, Alex Andersson, Lauren Rhodes, Thomas de Boer, M. Gromadzki, G. E. Anderson, Benjamin Schneider, R. P. Fender, H. Fausey, G. Pugliese, M. Fulton, B. Sbarufatti, S. R. Oates, A. de Ugarte Postigo, K. P. Mooley, A. J. Levan, Chien-Cheng Lin, J. H. Gillanders, A. Martín-Carrillo, P. T. O’Brien, M. E. Bell, Danny T. H. Steeghs, M. de Pasquale, Ashna Gulati, S. Yang, K. Ackley, Zhenning Wang, Tayyaba Zafar, James K. Leung, Benjamin P. Gompertz, D. Malesani, D. R. Williams, M. E. Huber, V. D’Elia, N. R. Tanvir, M. Ferro, R. Brivio, A. J. van der Horst, S. D. Ryder, Gavin P. Lamb, A. Rossi, R. A. M. J. Wijers, D. H. Hartmann, P. J. Hancock, N. J. Klingler, Steve Schulze, S. J. Smartt, S. D. Vergani, K. C. Chambers, A. Rowlinson, N. P. M. Kuin, David A. Green, C. C. Thöne, R. L. C. Starling, Hua Gao, M. Nicholl, R. J. Wainscoat, Eric Burns, K. Smith, Shubham Srivastav, I. Worssam, T. W. Chen, Dimple Dimple, Tamal Mukherjee, P. Mínguez
article en

Abstract

Abstract We present the early radio detection and multiwavelength modeling of the short gamma-ray burst (GRB) 231117A at redshift z = 0.257. The Australia Telescope Compact Array automatically triggered a 9 hr observation of GRB 231117A at 5.5 and 9 GHz following its detection by the Neil Gehrels Swift Observatory just 1.3 hr post-burst. Splitting this observation into 1 hr time bins, the early radio afterglow exhibited flaring, scintillating and plateau phases. The scintillation allowed us to place the earliest upper limit (&lt;10 hr) on the size of a GRB blast wave to date, constraining it to &lt;1 × 10 16 cm. Multiwavelength modeling of the full afterglow required a period of significant energy injection between ∼0.02 and 1 day. The energy injection was modeled as a violent collision of two shells: a reverse shock passing through the injection shell explains the early radio plateau, while an X-ray flare is consistent with a shock passing through the leading impulsive shell. Beyond 1 day, the blast wave evolves as a classic decelerating forward shock with an electron distribution index of p = 1.66 ± 0.01. Our model also indicates a jet break at ∼2 days, and a half-opening angle of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>j</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>16</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> <mml:mn>6</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> <mml:mn>1</mml:mn> </mml:math> . Following the period of injection, the total energy is ζ ∼ 18 times the initial impulsive energy, with a final collimation-corrected energy of E Kf ∼ 5.7 × 10 49 erg. The minimum Lorentz factors this model requires are consistent with constraints from the early radio measurements of Γ &gt; 35 to Γ &gt; 5 between ∼0.1 and 1 day. These results demonstrate the importance of rapid and sensitive radio follow-up of GRBs for exploring their central engines and outflow behaviour.

The Astrophysical JournalVol. 994(1)
University College Dublin (IE), Northwestern University (US), University of Messina (IT), University of Technology Sydney (AU), Louisiana State University (US), California Institute of Technology (US), University of Copenhagen (DK), Queen's University Belfast (GB), Commonwealth Scientific and Industrial Research Organisation (AU), Centre National de la Recherche Scientifique (FR), The University of Sydney (AU), Goddard Space Flight Center (US), University of Hawaii System (US), Radboud University Nijmegen (NL), University of Leicester (GB), University of Toronto (CA), George Washington University (US), Hebrew University of Jerusalem (IL), Curtin University (AU), Aix-Marseille Université (FR), National Central University (TW), University of Cambridge (GB), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris Sciences et Lettres (FR), Université Paris-Saclay (FR), Observatoire de Paris (FR), Agenzia Spaziale Italiana (IT), Brera Astronomical Observatory (IT), Evgeni Kharadze Georgian National Astrophysical Observatory (GE), University of Manchester (GB), University of Warwick (GB), Sorbonne Université (FR), University of Oxford (GB), Calar Alto Observatory (ES), Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna (IT), Henan Academy of Sciences (CN), Millennium Institute of Astrophysics (CL), Canadian Institute for Theoretical Astrophysics (CA), ARC Centre of Excellence for Gravitational Wave Discovery (AU), CEA Paris-Saclay (FR), European Southern Observatory (CL), Astronomical Institute of the Slovak Academy of Sciences (SK), Astronomy and Space (AU), International Centre for Radio Astronomy Research (AU), Institut de Recherche sur les Lois Fondamentales de l'Univers (FR), Deleted Institution, University College London (GB), University of Warsaw (PL), McGill University (CA), Liverpool John Moores University (GB), Massachusetts Institute of Technology (US), Lancaster University (GB), University of Birmingham (GB), Clemson University (US), National Institute for Astrophysics (IT), Netherlands Institute for Radio Astronomy (NL), Indian Institute of Technology Kanpur (IN), Macquarie University (AU)
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