Exploring the connection between compact object mergers and fast X-ray transients
Context. The connection between compact object mergers and some extragalactic fast X-ray transients (FXRTs) has long been hypothesised but never ultimately established. Aims. In this work, we investigate two FXRTs, the LEIA X-ray Transient LXT 240402A and the Einstein Probe EP 250207b, whose precise positions lie close to nearby ( z ≲ 0.1) quiescent galaxies with a negligible probability of chance coincidence, identifying them as particularly promising cases of merger-driven explosions in the local Universe. Methods. We used Chandra to derive accurate localisations for both events and secure otherwise ambiguous associations with their optical counterparts. Deep optical and near-infrared observations with VLT, GTC, and LBT were performed to characterise the surrounding environment and search for kilonova emission, the hallmark of neutron star mergers. Complementary early-time X-ray monitoring with Swift and Einstein Probe was used to constrain the non-thermal afterglow. Results. We find that both FXRTs remain compatible with a compact binary merger progenitor, which produced low-mass ejecta and kilonova emission subdominant to the afterglow. However, alternative explanations such as a distant ( z ≳ 1) core-collapse supernova cannot be conclusively ruled out.
Authors
- Richard S. Woolf (ORCID: https://orcid.org/0000-0003-4859-1711)
- Hu Lei (ORCID: https://orcid.org/0000-0003-3288-5205)
- Maria Gritsevich (ORCID: https://orcid.org/0000-0003-4268-6277)
- A. Tsvetkova (ORCID: https://orcid.org/0000-0003-0292-6221)
- E. Troja (ORCID: https://orcid.org/0000-0002-1869-7817)
- Qinyu Wu (ORCID: https://orcid.org/0009-0002-9275-715X)
- Chris L. Fryer (ORCID: https://orcid.org/0000-0003-2624-0056)
- J. E. Grove (ORCID: https://orcid.org/0000-0002-0586-193X)
- A. Ridnaia (ORCID: https://orcid.org/0000-0001-9477-5437)
- Melissa Kerr
- R. L. Becerra (ORCID: https://orcid.org/0000-0002-0216-3415)
- D. Frederiks (ORCID: https://orcid.org/0000-0002-1153-6340)
- Hui Sun (ORCID: https://orcid.org/0000-0002-9615-1481)
- Brendan O’Connor (ORCID: https://orcid.org/0000-0002-9700-0036)
- H. W. Lee
- D. Svinkin (ORCID: https://orcid.org/0000-0002-2208-2196)
- S. Dichiara (ORCID: https://orcid.org/0000-0001-6849-1270)
- Roberto Ricci
- C. C. Cheung (ORCID: https://orcid.org/0000-0002-4377-0174)
- A. J. Castro‐Tirado (ORCID: https://orcid.org/0000-0003-2999-3563)
- Margarita Pereyra (ORCID: https://orcid.org/0000-0001-6148-6532)
- R. Sánchez-Ramírez (ORCID: https://orcid.org/0000-0002-7158-5099)
- Camila Angulo-Valdez (ORCID: https://orcid.org/0009-0002-6667-3294)
- Yu-Han Yang
- Mikhail Ulanov
- M. G. Watson
- Muskan Yadav (ORCID: https://orcid.org/0009-0004-9520-5822)
- Bing Zhang (ORCID: https://orcid.org/0009-0006-6019-0629)
- Massine El Kabir
- Niccolò Passaleva (ORCID: https://orcid.org/0009-0007-6886-4082)
- D. María Caballero-García
- L. Alexandra Lysenko
Institutions
- University of Rome Tor Vergata (IT)
- United States Naval Research Laboratory (US)
- Pennsylvania State University (US)
- Ural Federal University (RU)
- University of Helsinki (FI)
- University of Nevada, Reno (US)
- Los Alamos National Laboratory (US)
- University of Cagliari (IT)
- Chinese Academy of Sciences (CN)
- Astronomy and Space (AU)
- Instituto de Astrofísica de Andalucía (ES)
- National Astronomical Observatories (CN)
- Carnegie Mellon University (US)
- Universidad de Málaga (ES)
- Sapienza University of Rome (IT)
- University of Hong Kong (HK)
- Universidad Nacional Autónoma de México (MX)
- Netherlands Institute for Radio Astronomy (NL)
- Ioffe Institute (RU)
Publication Details
- Journal
- Astronomy and Astrophysics
- Published
- 2025-12-08
- DOI
- https://doi.org/10.1051/0004-6361/202557612
- Primary Topic
- Gamma-ray bursts and supernovae
- Type
- article
- Field-Weighted Citation Impact
- 0.00