Year: 2026
Type: article
Abstract: We present a multiwavelength study of GRB 260310A, a nearby long-duration gamma-ray burst (GRB) at z ≃ 0.153 associated with a broad-lined Type Ic supernova. Despite its modest prompt gamma-ray output, E γ ,iso ≃ 3.5 × 10 50 erg, GRB 260310A exhibits one of the brightest afterglows ever observed in the X-ray, optical, and radio bands. Its apparent brightness is not its only remarkable feature. The optical afterglow displays a delayed onset, characterized by a slow rising phase, with slope α ≈ −1, and a late peak at ∼0.1 day. We argue that the combination of weak prompt emission, hard peak energy, and late afterglow onset is naturally explained by a GRB jet viewed off-axis. The radio spectral energy distributions are consistent with synchrotron radiation and indicate the presence of both reverse- shock (RS) and forward-shock (FS) components, thus providing a first test of RS models in an off-axis geometry. The X-ray afterglow displays a prominent rebrightening, monitored for up to ∼68 days with no evidence of spectral evolution. A low level of linear polarization, Π ≈ 1.7%, is measured at 15 GHz at T 0 + 55 days and suggests that, at these late times, the FS is the dominant emission component from radio to X-rays. This late-time rebrightening represents a critical test for the two-component jet model. If interpreted as the emergence of a narrow jet core viewed further off-axis, it would imply extreme luminosities and energetics for an on-axis observer.
Authors: Yu-Han Yang, Roberto Ricci, Eleonora Troja, Muskan Yadav, Yi-Han Iris Yin, Rubén Sánchez-Ramírez, Brendan O’Connor, Niccolò Passaleva, Alberto J. Castro-Tirado, Hendrik van Eerten, Simone Dichiara, Vincenzo Galluzzi, Narjes Shahamat Dehsorkh, Iván Agudo, Jesús Aceituno, Malte Busmann, Maria D. Caballero-García, Emilio Fernández-García, Daniel Gruen, Maria Gritsevich, Sergiy Guziy, David Hiriart, You-Dong Hu, Martin Jelínek, Alexander Kutyrev, Alzbeta Malenakova, Filip Novotny, Ignacio Pérez-García, Shashi B. Pandey, Jorma Ryske, Alfredo Sota, Jan Strobl, Hira Waseem, Siyu Wu
Institutions: University of Rome Tor Vergata, Istituto di Radioastronomia di Bologna, National Institute for Astrophysics, University of Hong Kong, Consejo Superior de Investigaciones Científicas, Instituto de Astrofísica de Andalucía, Carnegie Mellon University, Sapienza University of Rome, Universidad de Málaga, University of Bath, Pennsylvania State University, Trieste Astronomical Observatory, Excellence Cluster Origins, Ludwig-Maximilians-Universität München, Petro Mohyla Black Sea National University, Universidad Nacional Autónoma de México, Guangxi University, Czech Academy of Sciences, National Aeronautics and Space Administration, University of Maryland, College Park, Masaryk University, Aryabhatta Research Institute of Observational Sciences, Ursa Astronomical Association
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
Award: G5377502975
OpenAlex ID: W7162287227