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| Format: | Preprint |
| Published: |
2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2508.13039 |
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| _version_ | 1866914204576907264 |
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| author | Jonker, P. G. Levan, A. J. Liu, Xing Xu, Dong Liu, Yuan Xu, Xinpeng Li, An Sarin, N. Tanvir, N. R. Lamb, G. P. Ravasio, M. E. Sánchez-Sierras, J. Quirola-Vásquez, J. A. Rayson, B. C. van Dalen, J. N. D. Malesani, D. B. van Hoof, A. P. C. Bauer, F. E. Chacón, J. Smartt, S. J. Martin-Carrillo, A. Corcoran, G. Cotter, L. Rossi, A. Onori, F. Fraser, M. O'Brien, P. T. Eyles-Ferris, R. A. J. Hjorth, J. Chen, T. -W. Leloudas, G. Tomasella, L. Schulze, S. De Pasquale, M. Carotenuto, F. Bright, J. Wang, Chenwei Xiong, Shaolin Zhang, Jinpeng Xue, Wangchen Liu, Jiacong Li, Chengkui Sanchez, D. Mata Torres, M. A. P. |
| author_facet | Jonker, P. G. Levan, A. J. Liu, Xing Xu, Dong Liu, Yuan Xu, Xinpeng Li, An Sarin, N. Tanvir, N. R. Lamb, G. P. Ravasio, M. E. Sánchez-Sierras, J. Quirola-Vásquez, J. A. Rayson, B. C. van Dalen, J. N. D. Malesani, D. B. van Hoof, A. P. C. Bauer, F. E. Chacón, J. Smartt, S. J. Martin-Carrillo, A. Corcoran, G. Cotter, L. Rossi, A. Onori, F. Fraser, M. O'Brien, P. T. Eyles-Ferris, R. A. J. Hjorth, J. Chen, T. -W. Leloudas, G. Tomasella, L. Schulze, S. De Pasquale, M. Carotenuto, F. Bright, J. Wang, Chenwei Xiong, Shaolin Zhang, Jinpeng Xue, Wangchen Liu, Jiacong Li, Chengkui Sanchez, D. Mata Torres, M. A. P. |
| contents | Fast X-ray Transients (FXTs) are short-lived extra-galactic X-ray sources. Recent progress through multi-wavelength follow-up of Einstein Probe discovered FXTs has shown that several are related to collapsars, which can also produce gamma-ray bursts (GRBs). In this paper we investigate the nature of the FXT EP250207b. The VLT/MUSE spectra of a nearby (15.9 kpc in projection) lenticular galaxy reveal no signs of recent star formation. If this galaxy is indeed the host, EP250207b lies at a redshift of z=0.082, implying a peak observed absolute magnitude for the optical counterpart of M_r=-14.5. At the time when supernovae (SNe) would peak, it is substantially fainter than all SN types. These results are inconsistent with a collapsar origin for EP250207b. The properties favour a binary compact object merger driven origin. The X-ray, optical and radio observations are compared with predictions of several types of extra-galactic transients, including afterglow and kilonova models. The data can be fit with a slightly off-axis viewing angle afterglow. However, the late-time (~30 day) optical/NIR counterpart is too bright for the afterglow and also for conventional kilonova models. This could be remedied if that late emission is due to a globular cluster or the core of a (tidally disrupted) dwarf galaxy. If confirmed, this would be the first case where the multi-wavelength properties of an FXT are found to be consistent with a compact object merger origin, increasing the parallels between FXTs and GRBs. We finally discuss if the source could originate in a higher redshift host galaxy. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_13039 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | EP250207b is not a collapsar fast X-ray transient. Is it due to a compact object merger? Jonker, P. G. Levan, A. J. Liu, Xing Xu, Dong Liu, Yuan Xu, Xinpeng Li, An Sarin, N. Tanvir, N. R. Lamb, G. P. Ravasio, M. E. Sánchez-Sierras, J. Quirola-Vásquez, J. A. Rayson, B. C. van Dalen, J. N. D. Malesani, D. B. van Hoof, A. P. C. Bauer, F. E. Chacón, J. Smartt, S. J. Martin-Carrillo, A. Corcoran, G. Cotter, L. Rossi, A. Onori, F. Fraser, M. O'Brien, P. T. Eyles-Ferris, R. A. J. Hjorth, J. Chen, T. -W. Leloudas, G. Tomasella, L. Schulze, S. De Pasquale, M. Carotenuto, F. Bright, J. Wang, Chenwei Xiong, Shaolin Zhang, Jinpeng Xue, Wangchen Liu, Jiacong Li, Chengkui Sanchez, D. Mata Torres, M. A. P. High Energy Astrophysical Phenomena Fast X-ray Transients (FXTs) are short-lived extra-galactic X-ray sources. Recent progress through multi-wavelength follow-up of Einstein Probe discovered FXTs has shown that several are related to collapsars, which can also produce gamma-ray bursts (GRBs). In this paper we investigate the nature of the FXT EP250207b. The VLT/MUSE spectra of a nearby (15.9 kpc in projection) lenticular galaxy reveal no signs of recent star formation. If this galaxy is indeed the host, EP250207b lies at a redshift of z=0.082, implying a peak observed absolute magnitude for the optical counterpart of M_r=-14.5. At the time when supernovae (SNe) would peak, it is substantially fainter than all SN types. These results are inconsistent with a collapsar origin for EP250207b. The properties favour a binary compact object merger driven origin. The X-ray, optical and radio observations are compared with predictions of several types of extra-galactic transients, including afterglow and kilonova models. The data can be fit with a slightly off-axis viewing angle afterglow. However, the late-time (~30 day) optical/NIR counterpart is too bright for the afterglow and also for conventional kilonova models. This could be remedied if that late emission is due to a globular cluster or the core of a (tidally disrupted) dwarf galaxy. If confirmed, this would be the first case where the multi-wavelength properties of an FXT are found to be consistent with a compact object merger origin, increasing the parallels between FXTs and GRBs. We finally discuss if the source could originate in a higher redshift host galaxy. |
| title | EP250207b is not a collapsar fast X-ray transient. Is it due to a compact object merger? |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2508.13039 |