Analyse multi-bande du sursaut gamma brillant GRB 230812B et de la supernova associée

Le sursaut gamma long GRB230812B est très brillant et relativement proche (z=0.36). Cet événement a suscité un grand intérêt dans la communauté astrophysique et a été étudié dans tout le spectre électromagnétique. Cet article synthétise les résultats de 80 observations dans le domaine des rayons X, de l’ultraviolet et les longueurs d’onde submillimétriques avec le réseau de télescopes GRANDMA.


GRB 230812B is a bright and relatively nearby () long gamma-ray burst that has generated significant interest in the community and therefore has been subsequently observed over the entire electromagnetic spectrum. We report over 80 observations in X-ray, ultraviolet, optical, infrared, and sub-millimeter bands from the GRANDMA (Global Rapid Advanced Network for Multi-messenger Addicts) network of observatories and from observational partners. Adding complementary data from the literature, we then derive essential physical parameters associated with the ejecta and external properties (i.e. the geometry and environment) and compare with other analyses of this event (e.g. Srinivasaragavan et al. 2023). We spectroscopically confirm the presence of an associated supernova, SN2023pel, and we derive a photospheric expansion velocity of v 17 x 103 km s1. We analyze the photometric data first using empirical fits of the flux and then with full Bayesian Inference. We again strongly establish the presence of a supernova in the data, with an absolute peak r-band magnitude Mr=19.41±0.10. We find a flux-stretching factor or relative brightness kSN=1.04±0.09 and a time-stretching factor sSN=0.68±0.05, both compared to SN1998bw. Therefore, GRB 230812B appears to have a clear long GRB-supernova association, as expected in the standard collapsar model. However, as sometimes found in the afterglow modelling of such long GRBs, our best fit model favours a very low density environment (log10(nISM/cm3)=2.161.30+1.21). We also find small values for the jet’s core angle θcore=1.700.71+1.00 deg and viewing angle. GRB 230812B/SN2023pel is one of the best characterized afterglows with a distinctive supernova bump.

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