An extremely soft and weak fast X-ray transient associated with a luminous supernova
Abstract
Long gamma-ray bursts (LGRBs), including their subclasses of low-luminosity GRBs (LL-GRBs) and X-ray flashes (XRFs) characterized by low spectral peak energies, are known to be associated with broad-lined Type Ic supernovae (SNe Ic-BL), which result from the core collapse of massive stars that lose their outer hydrogen and helium envelopes. However, the soft and weak end of the GRB/XRF population remains largely unexplored, due to the limited sensitivity to soft X-ray emission. Here we report the discovery of a fast X-ray transient, EP250108a, detected by the Einstein Probe (EP) in the soft X-ray band at redshift , which was followed up by extensive multiband observations. EP250108a shares similar X-ray luminosity as XRF\,060218, the prototype of XRFs, but it extends GRBs/XRFs down to the unprecedentedly soft and weak regimes, with its and , respectively. Meanwhile, EP250108a is found to be associated with SN\,2025kg, one of the most luminous and possibly magnetar-powered SNe Ic-BL detected so far. Modeling of the well-sampled optical light curves favors a mildly relativistic outflow as the origin of this event. This discovery demonstrates that EP, with its unique capability, is opening a new observational window into the diverse outcomes of death of massive stars.
Cite
@article{arxiv.2504.17034,
title = {An extremely soft and weak fast X-ray transient associated with a luminous supernova},
author = {W. -X. Li and Z. -P. Zhu and X. -Z. Zou and J. -J. Geng and L. -D. Liu and Y. -H. Wang and R. -Z. Li and D. Xu and H. Sun and X. -F. Wang and Y. -W. Yu and B. Zhang and X. -F. Wu and Y. Yang and A. V. Filippenko and X. -W. Liu and W. -M. Yuan and D. Aguado and J. An and T. An and D. A. H. Buckley and A. J. Castro-Tirado and S. -Y. Fu and J. P. U. Fynbo and D. A. Howell and J. -W. Hu and S. -Q. Jiang and A. Kumar and J. -R. Mao and J. R. Maund and X. Liu and B. Mockler and A. Moskvitin and M. Andrews and C. R. Bom and T. G. Brink and K. Chatterjee and Y. Chen and H. -Q. Cheng and J. Cooke and J. L. Dai and G. -W. Du and N. Erasmus and Y. Fang and J. Farah and V. Goranskij and M. Gritsevich and M. Gu and Z. Guo and E. Hsiao and Y. -D. Hu and Y. -L. Hua and W. Jacobson-Galán and S. -M. Jia and C. -C. Jin and M. M. Kasliwal and C. D. Kilpatrick and B. Kumar and W. -H. Lei and C. -K. Li and D. -Y. Li and L. -P. Li and Z. -X. Ling and Q. -C. Liu and Y. Liu and Y. -Q. Liu and A. López-Oramas and O. Maslennikova and C. McCully and I. Monageng and M. Newsone and E. Padilla Gonzalez and H. -W. Pan and H. -W. Peng and G. Pignata and F. Poidevin and S. B. Potter and I. Pérez-Fournon and L. Santana-Silva and A. Santos and C. -Y. Song and F. -F. Song and O. Spiridonova and N. -C. Sun and X. -J. Sun and G. Terreran and L. -Z. Wang and L. -F. Wang and B. -T. Wang and Z. -Y. Wang and G. -L. Wu and D. -F. Xiang and H. -F. Xiao and Y. -F. Xu and S. -J. Xue and S. -Y. Yan and Y. -P. Yang and L. -X. Yu and Y. -H. Zhang and Y. -H. Zhang and C. Zhang and J. -H. Zhang and J. -J. Zhang and W. Zheng and H. Zou},
journal= {arXiv preprint arXiv:2504.17034},
year = {2025}
}
Comments
54 pages, 10 figures, submitted