Multi-wavelength Constraints on the Transient EP250905a

J. Quirola-Vasquez; P. G. Jonker; A. Levan; D. B. Malesani; F. E. Bauer; A. Martin-Carrillo; G. Corcoran; D. Mata Sanchez; R. A. J. Eyles-Ferris; F. Carotenuto; M. Ravasio; J. Sanchez-Sierras; J. Bright; J. A. Chacon; L. Cotter; F. J. Cowie; N. Sarin; M. A. P. Torres; J. N. D. van Dalen; A. P. C. van Hoof; V. D'Elia; P. Jakobsson; N. Habeeb; S. Kobayashi; A. Saccardi; M. De Pasquale; D. Xu; Y. H. Cheng; R. D. Liang; H. Sun; Y. Wang; W. Yuan; W. D. Zhang

Multi-wavelength Constraints on the Transient EP250905a

High Energy Astrophysical Phenomena 2026-07-09 v1

Authors: J. Quirola-Vasquez , P. G. Jonker , A. Levan , D. B. Malesani , F. E. Bauer , A. Martin-Carrillo , G. Corcoran , D. Mata Sanchez , R. A. J. Eyles-Ferris , F. Carotenuto , M. Ravasio , J. Sanchez-Sierras , J. Bright , J. A. Chacon , L. Cotter , F. J. Cowie , N. Sarin , M. A. P. Torres , J. N. D. van Dalen , A. P. C. van Hoof , V. D'Elia , P. Jakobsson , N. Habeeb , S. Kobayashi , A. Saccardi , M. De Pasquale , D. Xu , Y. H. Cheng , R. D. Liang , H. Sun , Y. Wang , W. Yuan , W. D. Zhang

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Abstract

Fast X-ray transients (FXTs) are a diverse class of high-energy suggested origins, ranging from stellar explosions to compact object mergers. The Einstein Probe (EP) satellite discovers approximately 100 FXTs per year. We aim to constrain the physical origin of EP250905a. We analyze X-ray, optical, near-infrared (NIR), and radio temporal and spectral properties of EP250905a. In addition, we assess the possible role of weak gravitational lensing in shaping its observed characteristics. EP250905a fades rapidly in X-rays, and we detect no NIR or radio emission, but we detect early optical emission that rapidly fades beyond the detection limits. Two nearby galaxies are identified for which we derive spectroscopic redshifts of $z=0.374$ (G1) and $z=2.714$ (G2). Our analysis favors G2 as the host of the FXT EP250905a. The angular separation of 2.56\arcsec\, between the FXT's optical counterpart and the center of the G1 galaxy suggests the emission of the FXT might be moderately magnified by lensing effects ( $\mu\approx3.9$ ) given the inferred Einstein radius of G1 ( $\theta_E\approx1.9$ arcsec). The data are best explained as an afterglow from a mildly off-axis structured jet at $z=2.714$ , providing a consistent broadband interpretation that also allows for weakly lensed emission of EP250905a.

Cite

@article{arxiv.2607.08090,
  title  = {Multi-wavelength Constraints on the Transient EP250905a},
  author = {J. Quirola-Vasquez and P. G. Jonker and A. Levan and D. B. Malesani and F. E. Bauer and A. Martin-Carrillo and G. Corcoran and D. Mata Sanchez and R. A. J. Eyles-Ferris and F. Carotenuto and M. Ravasio and J. Sanchez-Sierras and J. Bright and J. A. Chacon and L. Cotter and F. J. Cowie and N. Sarin and M. A. P. Torres and J. N. D. van Dalen and A. P. C. van Hoof and V. D'Elia and P. Jakobsson and N. Habeeb and S. Kobayashi and A. Saccardi and M. De Pasquale and D. Xu and Y. H. Cheng and R. D. Liang and H. Sun and Y. Wang and W. Yuan and W. D. Zhang},
  journal= {arXiv preprint arXiv:2607.08090},
  year   = {2026}
}

Comments

Accepted for publication in A&A