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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2511.13314 |
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| author | Quirola-Vásquez, J. Jonker, P. G. Levan, A. J. Malesani, D. B. Bauer, F. E. Sarin, N. Lamb, G. P. Martin-Carrillo, A. Sánchez-Sierras, J. Fraser, M. Izzo, L. Ravasio, M. E. Sánchez, D. Mata Torres, M. A. P. van Dalen, J. N. D. van Hoof, A. P. C. Chacón, J. A. Littlefair, S. Dhillon, V. S. Cotter, L. Corcoran, G. Eyles-Ferris, R. A. J. O'Brien, P. T. Stern, D. D'Elia, V. Hartmann, D. H. |
| author_facet | Quirola-Vásquez, J. Jonker, P. G. Levan, A. J. Malesani, D. B. Bauer, F. E. Sarin, N. Lamb, G. P. Martin-Carrillo, A. Sánchez-Sierras, J. Fraser, M. Izzo, L. Ravasio, M. E. Sánchez, D. Mata Torres, M. A. P. van Dalen, J. N. D. van Hoof, A. P. C. Chacón, J. A. Littlefair, S. Dhillon, V. S. Cotter, L. Corcoran, G. Eyles-Ferris, R. A. J. O'Brien, P. T. Stern, D. D'Elia, V. Hartmann, D. H. |
| contents | We present a multi-wavelength analysis of the fast X-ray transient EP 241021a, discovered by the Wide-field X-ray Telescope aboard the \emph{Einstein Probe} satellite on 2024 October 21. The event was not detected in gamma-rays. Follow-up observations from $\sim$1.5 to 100 days post-trigger were obtained across X-ray, UV, optical, near-infrared, and radio bands with ground- and space-based facilities. The redshift is constrained to $z = 0.7485$ from prominent optical spectral features. The optical light curve shows complex evolution: an initial $\sim t^{-0.7}$ decay, followed by a rapid re-brightening peaking at day 7.7 with $\sim t^{-1.7}$ decay, and a third phase peaking near day 19 with $\sim t^{-1.3}$ decay. The spectral energy distribution (SED) and its temporal evolution are consistent with a mix of non-thermal and thermal components. Early optical-to-X-ray spectral indices agree with optically thin synchrotron emission, while steepening of the optical SED after $\sim$20 days indicates either a shift in emission mechanism or the emergence of an additional component. Although broad-lined absorption features are absent, comparisons with type Ic-BL supernovae suggest a SN contribution at late times, suggesting a collapsar origin for EP 241021a. The likely SN in EP 241021a appears to require an additional energy source beyond $^{56}$Ni decay. These results support the view that some fast X-ray transients detected by the \emph{Einstein Probe} arise from massive stellar explosions. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_13314 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Unveiling the nature of the Einstein Probe transient EP 241021a Quirola-Vásquez, J. Jonker, P. G. Levan, A. J. Malesani, D. B. Bauer, F. E. Sarin, N. Lamb, G. P. Martin-Carrillo, A. Sánchez-Sierras, J. Fraser, M. Izzo, L. Ravasio, M. E. Sánchez, D. Mata Torres, M. A. P. van Dalen, J. N. D. van Hoof, A. P. C. Chacón, J. A. Littlefair, S. Dhillon, V. S. Cotter, L. Corcoran, G. Eyles-Ferris, R. A. J. O'Brien, P. T. Stern, D. D'Elia, V. Hartmann, D. H. High Energy Astrophysical Phenomena We present a multi-wavelength analysis of the fast X-ray transient EP 241021a, discovered by the Wide-field X-ray Telescope aboard the \emph{Einstein Probe} satellite on 2024 October 21. The event was not detected in gamma-rays. Follow-up observations from $\sim$1.5 to 100 days post-trigger were obtained across X-ray, UV, optical, near-infrared, and radio bands with ground- and space-based facilities. The redshift is constrained to $z = 0.7485$ from prominent optical spectral features. The optical light curve shows complex evolution: an initial $\sim t^{-0.7}$ decay, followed by a rapid re-brightening peaking at day 7.7 with $\sim t^{-1.7}$ decay, and a third phase peaking near day 19 with $\sim t^{-1.3}$ decay. The spectral energy distribution (SED) and its temporal evolution are consistent with a mix of non-thermal and thermal components. Early optical-to-X-ray spectral indices agree with optically thin synchrotron emission, while steepening of the optical SED after $\sim$20 days indicates either a shift in emission mechanism or the emergence of an additional component. Although broad-lined absorption features are absent, comparisons with type Ic-BL supernovae suggest a SN contribution at late times, suggesting a collapsar origin for EP 241021a. The likely SN in EP 241021a appears to require an additional energy source beyond $^{56}$Ni decay. These results support the view that some fast X-ray transients detected by the \emph{Einstein Probe} arise from massive stellar explosions. |
| title | Unveiling the nature of the Einstein Probe transient EP 241021a |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2511.13314 |