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DOE OSTI · 3028235

Exploring the connection between compact object mergers and fast X-ray transients

Becerra, R. L. [Department of Physics, University of Rome Tor Vergata; Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0000000202163415)·Yang, Y.-H. [Department of Physics, University of Rome Tor Vergata]·Troja, E. [Department of Physics, University of Rome Tor Vergata] (ORCID:0000000218697817)·El Kabir, M. [Department of Physics, University of Rome Tor Vergata; Department of Physics, University of Rome La Sapienza]·Dichiara, S. [Department of Astronomy and Astrophysics, The Pennsylvania State University] (ORCID:0000000168491270)·Passaleva, N. [Department of Physics, University of Rome Tor Vergata; Department of Physics, University of Rome La Sapienza] (ORCID:0009000768864082)·O’Connor, B. [McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University] (ORCID:0000000297000036)·Ricci, R. [Department of Physics, University of Rome Tor Vergata]·Fryer, Christopher Lee [Los Alamos National Laboratory] (ORCID:0000000326240056)·Hu, L. [McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University] (ORCID:0000000172011938)·Wu, Q. [National Astronomical Observatories, Chinese Academy of Sciences; School of Astronomy and Space Sciences, University of Chinese Academy of Sciences] (ORCID:000900029275715X)·Yadav, M. [Department of Physics, University of Rome Tor Vergata] (ORCID:0009000495205822)·Watson, A. M. [Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0000000220086927)·Tsvetkova, A. [Department of Physics, University of Cagliari; Ioffe Institute] (ORCID:0000000302926221)·Angulo-Valdez, C. [Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0009000266673294)·Caballero-García, M. D. [Instituto de Astrofísica de Andalucía (IAA-CSIC)] (ORCID:0000000179204564)·Castro-Tirado, A. J. [Instituto de Astrofísica de Andalucía (IAA-CSIC); Ingeniería de Sistemas y Automática, Universidad de Málaga, Unidad Asociada al CSIC por el IAA, Escuela de Ingenierías Industriales] (ORCID:0000000329993563)·Cheung, C. C. [Space Science Division, Naval Research Laboratory]·Frederiks, D. [Ioffe Institute] (ORCID:0000000211536340)·Gritsevich, M. [Faculty of Science, University of Helsinki; Institute of Physics and Technology, Ural Federal University] (ORCID:0000000342686277)·Grove, J. E. [Space Science Division, Naval Research Laboratory]·Kerr, M. [Space Science Division, Naval Research Laboratory] (ORCID:0000000208934073)·Lee, W. H. [Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0000000224675673)·Lysenko, A. L. [Ioffe Institute] (ORCID:0000000239428341)·Pereyra, M. [Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0000000161486532)·Ridnaia, A. [Ioffe Institute] (ORCID:0000000194775437)·Sánchez-Ramírez, R. [Instituto de Astrofísica de Andalucía (IAA-CSIC)] (ORCID:0000000271585099)·Sun, H. [Los Alamos National Laboratory] (ORCID:0000000296151481)·Svinkin, D. [Ioffe Institute] (ORCID:0000000222082196)·Ulanov, M. [Ioffe Institute] (ORCID:0000000200765228)·Woolf, R. [Space Science Division, Naval Research Laboratory]·Zhang, B. [Nevada Center for Astrophysics, University of Nevada; The Hong Kong Institute for Astronomy and Astrophysics, University of Hong Kong; Department of Physics, University of Hong Kong; Department of Physics and Astronomy, University of Nevada] (ORCID:0000000297252524)
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Abstract

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.

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79 ASTRONOMY AND ASTROPHYSICSgamma-ray burst: generalgamma-ray burst: individual: EP250207bgamma-ray burst: individual: LXT240402A

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BibTeXRIS

Becerra, R. L. [Department of Physics, University of Rome Tor Vergata; Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0000000202163415), Yang, Y.-H. [Department of Physics, University of Rome Tor Vergata], Troja, E. [Department of Physics, University of Rome Tor Vergata] (ORCID:0000000218697817), El Kabir, M. [Department of Physics, University of Rome Tor Vergata; Department of Physics, University of Rome La Sapienza], Dichiara, S. [Department of Astronomy and Astrophysics, The Pennsylvania State University] (ORCID:0000000168491270), Passaleva, N. [Department of Physics, University of Rome Tor Vergata; Department of Physics, University of Rome La Sapienza] (ORCID:0009000768864082), O’Connor, B. [McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University] (ORCID:0000000297000036), Ricci, R. [Department of Physics, University of Rome Tor Vergata], Fryer, Christopher Lee [Los Alamos National Laboratory] (ORCID:0000000326240056), Hu, L. [McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University] (ORCID:0000000172011938), Wu, Q. [National Astronomical Observatories, Chinese Academy of Sciences; School of Astronomy and Space Sciences, University of Chinese Academy of Sciences] (ORCID:000900029275715X), Yadav, M. [Department of Physics, University of Rome Tor Vergata] (ORCID:0009000495205822), Watson, A. M. [Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0000000220086927), Tsvetkova, A. [Department of Physics, University of Cagliari; Ioffe Institute] (ORCID:0000000302926221), Angulo-Valdez, C. [Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0009000266673294), Caballero-García, M. D. [Instituto de Astrofísica de Andalucía (IAA-CSIC)] (ORCID:0000000179204564), Castro-Tirado, A. J. [Instituto de Astrofísica de Andalucía (IAA-CSIC); Ingeniería de Sistemas y Automática, Universidad de Málaga, Unidad Asociada al CSIC por el IAA, Escuela de Ingenierías Industriales] (ORCID:0000000329993563), Cheung, C. C. [Space Science Division, Naval Research Laboratory], Frederiks, D. [Ioffe Institute] (ORCID:0000000211536340), Gritsevich, M. [Faculty of Science, University of Helsinki; Institute of Physics and Technology, Ural Federal University] (ORCID:0000000342686277), Grove, J. E. [Space Science Division, Naval Research Laboratory], Kerr, M. [Space Science Division, Naval Research Laboratory] (ORCID:0000000208934073), Lee, W. H. [Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0000000224675673), Lysenko, A. L. [Ioffe Institute] (ORCID:0000000239428341), Pereyra, M. [Instituto de Astronomía, Universidad Nacional Autónoma de México] (ORCID:0000000161486532), Ridnaia, A. [Ioffe Institute] (ORCID:0000000194775437), Sánchez-Ramírez, R. [Instituto de Astrofísica de Andalucía (IAA-CSIC)] (ORCID:0000000271585099), Sun, H. [Los Alamos National Laboratory] (ORCID:0000000296151481), Svinkin, D. [Ioffe Institute] (ORCID:0000000222082196), Ulanov, M. [Ioffe Institute] (ORCID:0000000200765228), Woolf, R. [Space Science Division, Naval Research Laboratory], Zhang, B. [Nevada Center for Astrophysics, University of Nevada; The Hong Kong Institute for Astronomy and Astrophysics, University of Hong Kong; Department of Physics, University of Hong Kong; Department of Physics and Astronomy, University of Nevada] (ORCID:0000000297252524). 2026-01-20. Exploring the connection between compact object mergers and fast X-ray transients. https://doi.org/10.1051/0004-6361%2F202557612

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