Theoretical Description of GRB 160625B with Wind-to-ISM Transition and Implications for a Magnetized Outflow

Abstract

GRB 160625B, one of the brightest bursts in recent years, was simultaneously observed by Fermi and Swift satellites, and ground-based optical telescopes in three different events separated by long periods of time. In this paper the non-thermal multiwavelength observations of GRB 160625B are described and a transition phase from wind-type-like medium to interstellar medium between the early (event II) and the late (event III) afterglow is found. The multiwavelength observations of the early afterglow are consistent with the afterglow evolution starting at ∼ 150 s in a stellar wind medium whereas the observations of the late afterglow are consistent with the afterglow evolution in interstellar medium (ISM). The wind-to-ISM transition is calculated to be at ∼ 8×10 3 s when the jet has decelerated, at a distance of ∼ 1 pc from the progenitor. Using the standard external shock model, the synchrotron and synchrotron self-Compton emission from reverse shock is required to model the GeV γ-ray and optical observations in the early afterglow, and synchrotron radiation from the adiabatic forward shock to describe the X-ray and optical observations in the late afterglow. The derived values of the magnetization parameter, the slope of the fast decay of the optical flash and the inferred magnetic fields suggest that Poynting flux-dominated jet models with arbitrary magnetization could account for the spectral properties exhibited by GRB 160625B.

Analysis and Modeling of the Multi-wavelength Observations of the Luminous GRB 190114C

“…The best-fit values found after modelling the LAT, GBM, X-ray, optical and radio observations with reverse and forward shocks indicate that the high-energy photons were originated in external shocks as was previously suggested for others GRBs (Kumar andBarniol Duran 2009, 2010;Zou et al 2009;Ghisellini et al 2010;He et al 2011;Nava et al 2014;Fraija et al 2016bFraija et al , 2017b. It is worth highlighting that the values found of t 0 are in the range of the first high-energy photons detected by Fermi LAT.…”

“…Given the best-fit values of the wind-like and homogeneous medium, the deceleration radius and the bulk Lorentz factor at the transition from the stratified to uniform medium is R tr 2.3 × 10 17 cm and Γ tr 220, respectively, which agree with the breaks in the X-ray and optical light curves. In comparison with other bursts that exhibited this transition (GRB 050319, 081109A and GRB 160626B; Kamble et al 2007;Jin et al 2009;Fraija et al 2017b), the value obtained for GRB 190114C corresponds to the nearest value to the progenitor.…”

Lorentz Factor Evolution of an Expanding Jet Shell Observed in a Gamma-Ray Burst: Case Study of GRB 160625B

“…Our obtained light curve of the second emission episode in GRB 160625B is shown in Figure 1, where t obs is the observer time by setting t obs = 0 at the burst first trigger (i.e., 22:40:16.28 UT on 25 June 2016Burn 2016. For the discussions about this burst, one can refer to, e.g., Troja et al (2017), Lü et al (2017), Fraija et al (2017) Wang et al (2017), Alexander et al (2017), Zhang et al (2018), and Ravasio et al (2018). From Figure 1, one can find that the FP2EE (i.e., ∼ 186 − 192 s, marked with the two vertical dashed lines) of GRB 160625B is very smooth and well-shaped, which is very different from the light curve formed in the photosphere, e.g., GRB 090902B (Abdo et al 2009a).…”

Constraints on microphysical parameters of GRBs using HAWC

“…The dynamics of the external shock for the ejecta expanding into a surrounding medium with homogeneous density has been widely explored [9]. Using the synchrotron spectra, the evolution of synchrotron energy breaks and the maximum flux, the light curve in the fast-cooling regime is proportional…”

“…interstellar medium; ISM, see [5]), a stellar wind profile (e,g [6,7,8]) or a combination of these two (e.g. [9]). According to Meszaros and Rees [10], the inverse Compton scattering could be the dominant cooling mechanism of accelerated electrons in the external shock wave when it gets close to the deceleration radius.…”