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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
| Published: |
2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2505.05444 |
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| _version_ | 1866909897235365888 |
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| author | Gianfagna, Giulia Piro, Luigi Bruni, Gabriele Thakur, Aishwarya Linesh Van Eerten, Hendrik Caballero-García, Maria D. Castro-Tirado, Alberto Chen, Yong Cheng, Ye-hao Gritsevich, Maria Guziy, Sergiy He, Han Hu, You-Dong Jia, Shumei Ling, Zhixing Maiorano, Elisabetta Paladino, Rosita Pandey, Shashi B. Tripodi, Roberta Rossi, Andrea Sánchez-Ramírez, Rubén Yang, Shuaikang Yuan, Jianghui Yuan, Weimin Zhang, Chen |
| author_facet | Gianfagna, Giulia Piro, Luigi Bruni, Gabriele Thakur, Aishwarya Linesh Van Eerten, Hendrik Caballero-García, Maria D. Castro-Tirado, Alberto Chen, Yong Cheng, Ye-hao Gritsevich, Maria Guziy, Sergiy He, Han Hu, You-Dong Jia, Shumei Ling, Zhixing Maiorano, Elisabetta Paladino, Rosita Pandey, Shashi B. Tripodi, Roberta Rossi, Andrea Sánchez-Ramírez, Rubén Yang, Shuaikang Yuan, Jianghui Yuan, Weimin Zhang, Chen |
| contents | X-ray flashes (XRFs) are fast X-ray transients thought to be softer analogs of gamma-ray bursts (GRBs). With its soft X-ray sensitivity, the Einstein Probe (EP) provides a unique opportunity to study these events. We report multiwavelength observations of EP241021a, a soft X-ray transient detected by EP, and interpret its afterglow in the context of leading XRF models. The prompt emission was observed by EP-WXT and Fermi-GBM, followed by a broad campaign across radio (uGMRT, ATCA, e-MERLIN, ALMA), optical (LBT, GTC, CAHA), and X-rays (EP-FXT). Light curves and spectra were analyzed with both empirical and physical models of GRBs and spherical expansions (both nonrelativistic and mildly relativistic cocoons). The afterglow shows multiple components, consistent with a structured jet interacting with a complex environment. The early optical and X-ray decline is explained by wide, low-Lorentz-factor ($γ\sim 40$) wings, while a rebrightening at approximately 7 days arises from the off-axis jet core. Radio data require an additional mildly relativistic cocoon ($γ\sim 2$), and a late (70 days) spectral component peaking at 50 GHz suggests a second, slower cocoon ($γ\sim 1$). |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_05444 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The soft X-ray transient EP241021a: A cosmic explosion with a complex off-axis jet and cocoon from a massive progenitor Gianfagna, Giulia Piro, Luigi Bruni, Gabriele Thakur, Aishwarya Linesh Van Eerten, Hendrik Caballero-García, Maria D. Castro-Tirado, Alberto Chen, Yong Cheng, Ye-hao Gritsevich, Maria Guziy, Sergiy He, Han Hu, You-Dong Jia, Shumei Ling, Zhixing Maiorano, Elisabetta Paladino, Rosita Pandey, Shashi B. Tripodi, Roberta Rossi, Andrea Sánchez-Ramírez, Rubén Yang, Shuaikang Yuan, Jianghui Yuan, Weimin Zhang, Chen High Energy Astrophysical Phenomena X-ray flashes (XRFs) are fast X-ray transients thought to be softer analogs of gamma-ray bursts (GRBs). With its soft X-ray sensitivity, the Einstein Probe (EP) provides a unique opportunity to study these events. We report multiwavelength observations of EP241021a, a soft X-ray transient detected by EP, and interpret its afterglow in the context of leading XRF models. The prompt emission was observed by EP-WXT and Fermi-GBM, followed by a broad campaign across radio (uGMRT, ATCA, e-MERLIN, ALMA), optical (LBT, GTC, CAHA), and X-rays (EP-FXT). Light curves and spectra were analyzed with both empirical and physical models of GRBs and spherical expansions (both nonrelativistic and mildly relativistic cocoons). The afterglow shows multiple components, consistent with a structured jet interacting with a complex environment. The early optical and X-ray decline is explained by wide, low-Lorentz-factor ($γ\sim 40$) wings, while a rebrightening at approximately 7 days arises from the off-axis jet core. Radio data require an additional mildly relativistic cocoon ($γ\sim 2$), and a late (70 days) spectral component peaking at 50 GHz suggests a second, slower cocoon ($γ\sim 1$). |
| title | The soft X-ray transient EP241021a: A cosmic explosion with a complex off-axis jet and cocoon from a massive progenitor |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2505.05444 |