Exploring the connection between compact object mergers and fast X-ray transients: The cases of LXT 240402A and EP250207b
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| Format: | Preprint |
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2025
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| author | Becerra, R. L. Yang, Yu-Han Troja, Eleonora Kabir, Massine El Dichiara, Simone Passaleva, Niccolò O'Connor, Brendan Ricci, Roberto Fryer, Chris Hu, Lei Wu, Qinyu Yadav, Muskan Watson, Alan M. Tsvetkova, Anastasia Angulo-Valdez, Camila Caballero-García, María D. Castro-Tirado, Alberto J. Cheung, C. C. Frederiks, Dmitry Gritsevich, Maria Grove, J. E. Kerr, M. Lee, William H. Lysenko, Alexandra L. Talamantes, Margarita Pereyra Ridnaia, Anna Sánchez-Ramírez, Rubén Sun, Hui Svinkin, Dmitry Ulanov, Mikhail Woolf, R. Zhang, Bing |
| author_facet | Becerra, R. L. Yang, Yu-Han Troja, Eleonora Kabir, Massine El Dichiara, Simone Passaleva, Niccolò O'Connor, Brendan Ricci, Roberto Fryer, Chris Hu, Lei Wu, Qinyu Yadav, Muskan Watson, Alan M. Tsvetkova, Anastasia Angulo-Valdez, Camila Caballero-García, María D. Castro-Tirado, Alberto J. Cheung, C. C. Frederiks, Dmitry Gritsevich, Maria Grove, J. E. Kerr, M. Lee, William H. Lysenko, Alexandra L. Talamantes, Margarita Pereyra Ridnaia, Anna Sánchez-Ramírez, Rubén Sun, Hui Svinkin, Dmitry Ulanov, Mikhail Woolf, R. Zhang, Bing |
| contents | The connection between compact object mergers and some extragalactic fast X-ray transients (FXRTs) has long been hypothesized, but never ultimately established. In this work, we investigate two FXRTs, the LEIA X-ray Transient LXT 240402A and the Einstein Probe EP250207b, whose precise positions lie close to nearby ($z\!\lesssim\!0.1$) quiescent galaxies with negligible probability of chance coincidence, identifying them as particularly promising cases of merger-driven explosions in the local Universe. We used Chandra to derive accurate localizations 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 characterize 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. 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 ($z\!\gtrsim\!1$) core-collapse supernova cannot be conclusively ruled out. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_13015 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Exploring the connection between compact object mergers and fast X-ray transients: The cases of LXT 240402A and EP250207b Becerra, R. L. Yang, Yu-Han Troja, Eleonora Kabir, Massine El Dichiara, Simone Passaleva, Niccolò O'Connor, Brendan Ricci, Roberto Fryer, Chris Hu, Lei Wu, Qinyu Yadav, Muskan Watson, Alan M. Tsvetkova, Anastasia Angulo-Valdez, Camila Caballero-García, María D. Castro-Tirado, Alberto J. Cheung, C. C. Frederiks, Dmitry Gritsevich, Maria Grove, J. E. Kerr, M. Lee, William H. Lysenko, Alexandra L. Talamantes, Margarita Pereyra Ridnaia, Anna Sánchez-Ramírez, Rubén Sun, Hui Svinkin, Dmitry Ulanov, Mikhail Woolf, R. Zhang, Bing High Energy Astrophysical Phenomena The connection between compact object mergers and some extragalactic fast X-ray transients (FXRTs) has long been hypothesized, but never ultimately established. In this work, we investigate two FXRTs, the LEIA X-ray Transient LXT 240402A and the Einstein Probe EP250207b, whose precise positions lie close to nearby ($z\!\lesssim\!0.1$) quiescent galaxies with negligible probability of chance coincidence, identifying them as particularly promising cases of merger-driven explosions in the local Universe. We used Chandra to derive accurate localizations 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 characterize 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. 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 ($z\!\gtrsim\!1$) core-collapse supernova cannot be conclusively ruled out. |
| title | Exploring the connection between compact object mergers and fast X-ray transients: The cases of LXT 240402A and EP250207b |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2510.13015 |