Long-term Radio Monitoring of the Fast X-Ray Transient EP 240315a: Evidence for a Relativistic Jet
The recent launch of Einstein Probe (EP) in early 2024 opened up a new window onto the transient X-ray sky, allowing for real-time discovery and follow-up of fast X-ray transients (FXRTs). Multiwavelength observations of FXRTs and their counterparts are key to characterize the properties of their ou...
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2025-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/ad8b3f |
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| author | Roberto Ricci Eleonora Troja Yu-Han Yang Muskan Yadav Yuan Liu Hui Sun Xuefeng Wu He Gao Bing Zhang Weimin Yuan |
| author_facet | Roberto Ricci Eleonora Troja Yu-Han Yang Muskan Yadav Yuan Liu Hui Sun Xuefeng Wu He Gao Bing Zhang Weimin Yuan |
| author_sort | Roberto Ricci |
| collection | DOAJ |
| description | The recent launch of Einstein Probe (EP) in early 2024 opened up a new window onto the transient X-ray sky, allowing for real-time discovery and follow-up of fast X-ray transients (FXRTs). Multiwavelength observations of FXRTs and their counterparts are key to characterize the properties of their outflows and, ultimately, identify their progenitors. Here, we report our long-term radio monitoring of EP 240315A, a long-lasting (∼1000 s) high-redshift ( z = 4.9) FXRT associated to gamma-ray burst (GRB) 240315C. Our campaign, carried out with the Australian Telescope Compact Array, followed the transient’s evolution at two different frequencies (5.5 and 9 GHz) for 3 months. In the radio light curves we identify an unusual steep rise at 9 GHz, possibly due to a refreshed reverse shock, and a late-time rapid decay of the radio flux, which we interpret as a jet break due to the outflow collimation. We find that the multiwavelength counterpart of EP 240315A is well described by a model of relativistic jet seen close to its axis, with jet half-opening angle θ _j ≈ 3° and beaming-corrected total energy E ≃ 4 × 10 ^51 erg, typical of GRBs. These results show that a substantial fraction of FXRTs may be associated to standard GRBs and that sensitive X-ray monitors, such as EP and the proposed HiZ-GUNDAM and Theseus missions, can successfully pinpoint their relativistic outflows up to high redshifts. |
| format | Article |
| id | doaj-art-cdfba66579074304a1efdad2148f5165 |
| institution | Kabale University |
| issn | 2041-8205 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal Letters |
| spelling | doaj-art-cdfba66579074304a1efdad2148f51652025-01-23T13:21:32ZengIOP PublishingThe Astrophysical Journal Letters2041-82052025-01-019792L2810.3847/2041-8213/ad8b3fLong-term Radio Monitoring of the Fast X-Ray Transient EP 240315a: Evidence for a Relativistic JetRoberto Ricci0https://orcid.org/0000-0003-4631-1528Eleonora Troja1https://orcid.org/0000-0002-1869-7817Yu-Han Yang2https://orcid.org/0000-0003-0691-6688Muskan Yadav3https://orcid.org/0009-0004-9520-5822Yuan Liu4https://orcid.org/0009-0007-6104-337XHui Sun5https://orcid.org/0000-0002-9615-1481Xuefeng Wu6https://orcid.org/0000-0002-6299-1263He Gao7https://orcid.org/0000-0002-3100-6558Bing Zhang8https://orcid.org/0000-0002-9725-2524Weimin Yuan9Dipartimento di Fisica, Universitá di Tor Vergata , Via della Ricerca Scientifica, 1, 00133 Rome, Italy; INAF—Istituto di Radioastronomia , Via Gobetti, 101, 40129, Bologna, ItalyDipartimento di Fisica, Universitá di Tor Vergata , Via della Ricerca Scientifica, 1, 00133 Rome, Italy; INAF—Istituto Nazionale di Astrofisica , 00133, Rome, ItalyDipartimento di Fisica, Universitá di Tor Vergata , Via della Ricerca Scientifica, 1, 00133 Rome, ItalyDipartimento di Fisica, Universitá di Tor Vergata , Via della Ricerca Scientifica, 1, 00133 Rome, ItalyNational Astronomical Observatories, Chinese Academy of Sciences , 100101 Beijing, People's Republic of ChinaNational Astronomical Observatories, Chinese Academy of Sciences , 100101 Beijing, People's Republic of ChinaPurple Mountain Observatory, Chinese Academy of Sciences , 210023 Nanjing, People's Republic of ChinaInstitute for Frontier in Astronomy and Astrophysics, Beijing Normal University , 100875 Beijing, People's Republic of China; School of Physics and Astronomy, Beijing Normal University , 100875 Beijing, People's Republic of ChinaNevada Center for Astrophysics and Department of Physics and Astronomy, University of Nevada Las Vegas , Las Vegas, NV 89154, USANational Astronomical Observatories, Chinese Academy of Sciences , 100101 Beijing, People's Republic of China; School of Astronomy and Space Sciences, University of Chinese Academy of Sciences , Beijing, 100049, People's Republic of ChinaThe recent launch of Einstein Probe (EP) in early 2024 opened up a new window onto the transient X-ray sky, allowing for real-time discovery and follow-up of fast X-ray transients (FXRTs). Multiwavelength observations of FXRTs and their counterparts are key to characterize the properties of their outflows and, ultimately, identify their progenitors. Here, we report our long-term radio monitoring of EP 240315A, a long-lasting (∼1000 s) high-redshift ( z = 4.9) FXRT associated to gamma-ray burst (GRB) 240315C. Our campaign, carried out with the Australian Telescope Compact Array, followed the transient’s evolution at two different frequencies (5.5 and 9 GHz) for 3 months. In the radio light curves we identify an unusual steep rise at 9 GHz, possibly due to a refreshed reverse shock, and a late-time rapid decay of the radio flux, which we interpret as a jet break due to the outflow collimation. We find that the multiwavelength counterpart of EP 240315A is well described by a model of relativistic jet seen close to its axis, with jet half-opening angle θ _j ≈ 3° and beaming-corrected total energy E ≃ 4 × 10 ^51 erg, typical of GRBs. These results show that a substantial fraction of FXRTs may be associated to standard GRBs and that sensitive X-ray monitors, such as EP and the proposed HiZ-GUNDAM and Theseus missions, can successfully pinpoint their relativistic outflows up to high redshifts.https://doi.org/10.3847/2041-8213/ad8b3fGamma-ray bursts |
| spellingShingle | Roberto Ricci Eleonora Troja Yu-Han Yang Muskan Yadav Yuan Liu Hui Sun Xuefeng Wu He Gao Bing Zhang Weimin Yuan Long-term Radio Monitoring of the Fast X-Ray Transient EP 240315a: Evidence for a Relativistic Jet The Astrophysical Journal Letters Gamma-ray bursts |
| title | Long-term Radio Monitoring of the Fast X-Ray Transient EP 240315a: Evidence for a Relativistic Jet |
| title_full | Long-term Radio Monitoring of the Fast X-Ray Transient EP 240315a: Evidence for a Relativistic Jet |
| title_fullStr | Long-term Radio Monitoring of the Fast X-Ray Transient EP 240315a: Evidence for a Relativistic Jet |
| title_full_unstemmed | Long-term Radio Monitoring of the Fast X-Ray Transient EP 240315a: Evidence for a Relativistic Jet |
| title_short | Long-term Radio Monitoring of the Fast X-Ray Transient EP 240315a: Evidence for a Relativistic Jet |
| title_sort | long term radio monitoring of the fast x ray transient ep 240315a evidence for a relativistic jet |
| topic | Gamma-ray bursts |
| url | https://doi.org/10.3847/2041-8213/ad8b3f |
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