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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
| Published: |
2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2604.21624 |
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| _version_ | 1866913057858387968 |
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| author | Zhao, Guoying Cao, Duo-Le Shen, Rong-Feng Sun, Hui Jin, Chi-Chuan Yuan, Wei-Min Wang, Chen-Wei Xiong, Shao-Lin Svinkin, Dmitry Xu, Dong Jiang, Shuai-Qing Jonker, Peter G. Wang, Yun Zhou, Hao Zhou, Chang Chen, Xinlei Chatterjee, Kaushik Wu, Xue-Feng Wang, Xiao-Feng Chen, Chun Liu, Yuan Levan, Andrew J. Chavez, Jennifer Alexandra Chacon Quirola-Vásquez, Jonathan Bauer, Franz E. Martin-Carrillo, Antonio Corcoran, Gregory Malesani, Daniele B. Frederiks, Dmitry Ridnaia, Anna Lysenko, Alexandra L. Ulanov, Mikhail |
| author_facet | Zhao, Guoying Cao, Duo-Le Shen, Rong-Feng Sun, Hui Jin, Chi-Chuan Yuan, Wei-Min Wang, Chen-Wei Xiong, Shao-Lin Svinkin, Dmitry Xu, Dong Jiang, Shuai-Qing Jonker, Peter G. Wang, Yun Zhou, Hao Zhou, Chang Chen, Xinlei Chatterjee, Kaushik Wu, Xue-Feng Wang, Xiao-Feng Chen, Chun Liu, Yuan Levan, Andrew J. Chavez, Jennifer Alexandra Chacon Quirola-Vásquez, Jonathan Bauer, Franz E. Martin-Carrillo, Antonio Corcoran, Gregory Malesani, Daniele B. Frederiks, Dmitry Ridnaia, Anna Lysenko, Alexandra L. Ulanov, Mikhail |
| contents | We present multi-wavelength study of the $γ$/X-ray transient EP250416a (also designated GRB 250416C), triggered by the Einstein Probe (EP) Wide-field X-ray Telescope and also by SVOM and Konus-Wind. Observations spanning the gamma-ray, X-ray, and optical bands facilitated detailed analysis of the burst's prompt emission, afterglow evolution, and physical origin. EP250416a exhibits a burst duration of 30 s in X-ray and 17.7 s in gamma-rays, with joint spectral fitting of 0.5-5000 keV data gives $E\rm_{peak}=342_{-232}^{+90}$ keV. Optical spectroscopy of the afterglow, acquired with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South, yielded a redshift of $z=0.963$. Accounting for the measured redshift, the isotropic energies are $E\rm_{X,iso}=2.7_{-0.5}^{+0.9}\times10^{50}$ erg and $E\rm_{γ,iso}=7.34_{-2.1}^{+5.1}\times10^{51}$ erg, aligning with the Amati relation for long GRBs. The fluence ratio $\rm S(25-50~keV)/S(50-100~keV)=0.78_{-0.15}^{+0.1}$ classifies EP250416a as an X-ray rich (XRR) GRB. The X-ray afterglow shows an initial shallow decay ($α\approx -0.5$) transitioning to a canonical decay phase ($α\approx -1$), with a very late jet break at $t\sim 1.5\times 10^6$ s, corresponding to a jet half-opening angle of $θ_j=10.6_{-1.8}^{+1.9}$ degrees. EP250416a is optically dark, as it shows only a faint $r$-band detection ($r=24.16$ mag) from Gemini South-GMOS and a low optical-to-X-ray spectral index $β_{\rm OX} = 0.3$. This may be attributed to significant host-galaxy extinction, with a required $A_V^{\text{host}}=5.5\ \text{mag}$ derived from the extinction curve model. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_21624 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Multi-wavelength study of EP250416a / GRB 250416C: An Optically Dark Long GRB with a Late Jet Break Zhao, Guoying Cao, Duo-Le Shen, Rong-Feng Sun, Hui Jin, Chi-Chuan Yuan, Wei-Min Wang, Chen-Wei Xiong, Shao-Lin Svinkin, Dmitry Xu, Dong Jiang, Shuai-Qing Jonker, Peter G. Wang, Yun Zhou, Hao Zhou, Chang Chen, Xinlei Chatterjee, Kaushik Wu, Xue-Feng Wang, Xiao-Feng Chen, Chun Liu, Yuan Levan, Andrew J. Chavez, Jennifer Alexandra Chacon Quirola-Vásquez, Jonathan Bauer, Franz E. Martin-Carrillo, Antonio Corcoran, Gregory Malesani, Daniele B. Frederiks, Dmitry Ridnaia, Anna Lysenko, Alexandra L. Ulanov, Mikhail High Energy Astrophysical Phenomena We present multi-wavelength study of the $γ$/X-ray transient EP250416a (also designated GRB 250416C), triggered by the Einstein Probe (EP) Wide-field X-ray Telescope and also by SVOM and Konus-Wind. Observations spanning the gamma-ray, X-ray, and optical bands facilitated detailed analysis of the burst's prompt emission, afterglow evolution, and physical origin. EP250416a exhibits a burst duration of 30 s in X-ray and 17.7 s in gamma-rays, with joint spectral fitting of 0.5-5000 keV data gives $E\rm_{peak}=342_{-232}^{+90}$ keV. Optical spectroscopy of the afterglow, acquired with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South, yielded a redshift of $z=0.963$. Accounting for the measured redshift, the isotropic energies are $E\rm_{X,iso}=2.7_{-0.5}^{+0.9}\times10^{50}$ erg and $E\rm_{γ,iso}=7.34_{-2.1}^{+5.1}\times10^{51}$ erg, aligning with the Amati relation for long GRBs. The fluence ratio $\rm S(25-50~keV)/S(50-100~keV)=0.78_{-0.15}^{+0.1}$ classifies EP250416a as an X-ray rich (XRR) GRB. The X-ray afterglow shows an initial shallow decay ($α\approx -0.5$) transitioning to a canonical decay phase ($α\approx -1$), with a very late jet break at $t\sim 1.5\times 10^6$ s, corresponding to a jet half-opening angle of $θ_j=10.6_{-1.8}^{+1.9}$ degrees. EP250416a is optically dark, as it shows only a faint $r$-band detection ($r=24.16$ mag) from Gemini South-GMOS and a low optical-to-X-ray spectral index $β_{\rm OX} = 0.3$. This may be attributed to significant host-galaxy extinction, with a required $A_V^{\text{host}}=5.5\ \text{mag}$ derived from the extinction curve model. |
| title | Multi-wavelength study of EP250416a / GRB 250416C: An Optically Dark Long GRB with a Late Jet Break |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2604.21624 |