GRB 190919B: Rapid optical rise explained as a flaring activity

• Authors: JELÍNEK Martin; TOPINKA Martin; KARPOV Sergey; MALEŇÁKOVÁ Alžběta; HU Y.-D.; RIGOSELLI Michela; ŠTROBL Jan; EBR Jan; CUNNIFFE Ronan; THOENE Christina; MAŠEK Martin; JANEČEK Petr; FERNANDEZ-GARCÍA Emilio; HIRIART David; LEE William H.; VÍTEK Stanislav; HUDEC René; TRÁVNÍČEK Petr; CASTRO-TIRADO Alberto J.; PROUZA Michael
• Year of publication: 2022
• Type: Article in Periodical
• Magazine / Source: Astronomy and Astrophysics
• MU Faculty or unit: Faculty of Science
• Web: https://www.aanda.org/articles/aa/full_html/2022/06/aa43010-21/aa43010-21.html
• Doi: http://dx.doi.org/10.1051/0004-6361/202143010
• Keywords: techniques; photometric; gamma-ray burst; individual; GRB190919B
• Description: Following the detection of a long GRB 190919B by INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory), we obtained an optical photometric sequence of its optical counterpart. The light curve of the optical emission exhibits an unusually steep rise similar to 100 s after the initial trigger. This behaviour is not expected from a 'canonical' GRB optical afterglow. As an explanation, we propose a scenario consisting of two superimposed flares: an optical flare originating from the inner engine activity followed by the hydrodynamic peak of an external shock. The inner-engine nature of the first pulse is supported by a marginal detection of flux in hard X-rays. The second pulse eventually concludes in a slow constant decay, which, as we show, follows the closure relations for a slow cooling plasma expanding into the constant interstellar medium and can be seen as an optical afterglow sensu stricto.