GRB 180728A and SN 2018fip: the nearest high-energy cosmological gamma-ray burst with an associated supernova

A. Rossi; L. Izzo; K. Maeda; P. Schady; D. B. Malesani; D. A. Kann; S. Klose; L. Amati; P. D'Avanzo; A. de Ugarte Postigo; K. E. Heintz; A. Kumar; V. Lipunov; A. Martin-Carrillo; A. Melandri; A. M. Nicuesa Guelbenzu; S. R. Oates; S. Schulze; J. Selsing; R. L. C. Starling; G. Stratta; D. Vlasenko; P. Balanutsa; R. Brivio; V. D'Elia; B. Milvang-Jensen; E. Palazzi; D. A. Perley; A. Rau; J. Sollerman; N. R. Tanvir; T. Zafar

doi:10.1051/0004-6361/202557667

paper

GRB 180728A and SN 2018fip: the nearest high-energy cosmological gamma-ray burst with an associated supernova

arXiv:2601.04179 · doi:10.1051/0004-6361/202557667

Abstract

The long GRB 180728A, at a redshift of $z = 0.1171$ , stands out due to its high isotropic energy of $E_{γ, i so} \sim 2.5 \times 1 0^{51}$ erg, in contrast with most events at redshift $z < 0.2$ . We analyze the properties of GRB 180728A's prompt emission, afterglow, and associated supernova SN 2018fip, comparing them with other GRB-SN events. This study employs a dense photometric and spectroscopic follow-up of the afterglow and the SN up to 80 days after the burst, supported by image subtraction to remove the presence of a nearby bright star, and modelling of both the afterglow and the supernova. GRB 180728A lies on the $E_{p, i} - E_{γ, i so}$ plane occupied by classical collapsar events, and the prompt emission is one of the most energetic at $z < 0.2$ after GRB 030329 and GRB 221009A. The afterglow of GRB 180728A is less luminous than that of most long GRBs, showing a shallow early phase that steepens around 5 hours (0.2 days). The GRB exploded in an irregular, low-mass, blue, star-forming galaxy, typical of low-z collapsar events. Because of the relatively faint afterglow, the light curve bump of SN 2018fip dominates the optical emission already after $\sim$ 3 days and is one of the best sampled to date. The strong suppression below $\sim$ 4000 angstrom and a largely featureless continuum in the early 6--9 days spectra favor aspherical two-component ejecta with a high-velocity collimated component ( $> 20, 000 k m s^{- 1}$ ), dominant early-on, and a more massive, low-velocity component, which dominates at much later epochs. Our findings indicate that asymmetries need to be considered in order to better understand GRB-SNe. In any case, SN 2018fip shares many characteristics with typical GRB-SNe. Its kinetic energy is below the common range of $1 0^{52} - 1 0^{53}$ erg and does not correlate with the high energy of the GRB, highlighting the diversity of the GRB-SN energy budget partition.

arXiv comment21 pages, 21 figures, 6 tables, submitted to Astronomy & Astrophysics

GRB 180728A and SN 2018fip: the nearest high-energy cosmological gamma-ray burst with an associated supernova

Abstract

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