| Title: |
The soft X-ray transient EP241021a: A cosmic explosion with a complex off-axis jet and cocoon from a massive progenitor |
| Authors: |
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 |
| Publication Year: |
2025 |
| Collection: |
ArXiv.org (Cornell University Library) |
| Subject Terms: |
High Energy Astrophysical Phenomena |
| Description: |
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 ($γ\sim 1$). ; 18 pages, 12 figures. Accepted for publication in Astronomy & Astrophysics |
| Document Type: |
text |
| Language: |
unknown |
| Relation: |
http://arxiv.org/abs/2505.05444; A&A 703, A92 (2025) |
| DOI: |
10.1051/0004-6361/202555450 |
| Availability: |
http://arxiv.org/abs/2505.05444; https://doi.org/10.1051/0004-6361/202555450 |
| Accession Number: |
edsbas.9C3D3EE1 |
| Database: |
BASE |