Evidence for GeV Gamma-Ray Emission from Intense GRB 240529A During the Afterglow's Shallow Decay Phase
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arXiv
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| Autores principales: | , , |
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| Formato: | Preprint |
| Publicado: |
2025
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| _version_ | 1866913794951741440 |
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| author | Terauchi, Kenta Oka, Tomohiko Asano, Katsuaki |
| author_facet | Terauchi, Kenta Oka, Tomohiko Asano, Katsuaki |
| contents | X-ray light curves of gamma-ray burst (GRB) afterglows exhibit various features, with the shallow decay phase being particularly puzzling. While some studies report absence of the X-ray shallow decay for hyper-energetic GRBs, recently discovered GRB 240529A shows a clear shallow decay phase with an isotropic gamma-ray energy of \SI{2.2e54}{erg}, making it a highly unusual case compared to typical GRBs. In order to investigate the physical mechanism of the shallow decay, we perform the \textit{Fermi}-LAT analysis of GRB 240529A along with \textit{Swift}-XRT analysis. We find no jet break feature in the X-ray light curve and then give the lower bound of the collimation-corrected jet energy of $>10^{52}$~erg, which is close to the maximum rotational energy of a magnetar. Our LAT data analysis reveals evidence of GeV emission with a statistical significance of $4.5σ$ during the shallow decay phase, which can be interpreted as the first case for hyper-energetic GRBs with a typical shallow decay phase. The GeV to keV flux ratio is calculated to be $4.2\pm2.3$. Together with X-ray spectral index, this indicates an inverse Compton origin of the GeV emission. Multiwavelength modeling based on time-dependent simulations tested two promising models, the energy injection and wind models. Both models can explain the X-ray and gamma-ray data, while our modeling demonstrates that gamma-ray observations, along with future GeV--TeV observations by CTAO, will distinguish between them. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_10907 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Evidence for GeV Gamma-Ray Emission from Intense GRB 240529A During the Afterglow's Shallow Decay Phase Terauchi, Kenta Oka, Tomohiko Asano, Katsuaki High Energy Astrophysical Phenomena X-ray light curves of gamma-ray burst (GRB) afterglows exhibit various features, with the shallow decay phase being particularly puzzling. While some studies report absence of the X-ray shallow decay for hyper-energetic GRBs, recently discovered GRB 240529A shows a clear shallow decay phase with an isotropic gamma-ray energy of \SI{2.2e54}{erg}, making it a highly unusual case compared to typical GRBs. In order to investigate the physical mechanism of the shallow decay, we perform the \textit{Fermi}-LAT analysis of GRB 240529A along with \textit{Swift}-XRT analysis. We find no jet break feature in the X-ray light curve and then give the lower bound of the collimation-corrected jet energy of $>10^{52}$~erg, which is close to the maximum rotational energy of a magnetar. Our LAT data analysis reveals evidence of GeV emission with a statistical significance of $4.5σ$ during the shallow decay phase, which can be interpreted as the first case for hyper-energetic GRBs with a typical shallow decay phase. The GeV to keV flux ratio is calculated to be $4.2\pm2.3$. Together with X-ray spectral index, this indicates an inverse Compton origin of the GeV emission. Multiwavelength modeling based on time-dependent simulations tested two promising models, the energy injection and wind models. Both models can explain the X-ray and gamma-ray data, while our modeling demonstrates that gamma-ray observations, along with future GeV--TeV observations by CTAO, will distinguish between them. |
| title | Evidence for GeV Gamma-Ray Emission from Intense GRB 240529A During the Afterglow's Shallow Decay Phase |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2504.10907 |