Radiative striped wind model for gamma-ray bursts

Abstract

In this paper we revisit the striped wind model in which the wind is accelerated by magnetic reconnection. In our treatment, radiation is included as an independent component, and two scenarios are considered. In the first one, radiation cannot stream efficiently through the reconnection layer, while the second scenario assumes that radiation is homogeneous in the striped wind. We show how these two assumptions affect the dynamics. In particular, we find that the asymptotic radial evolution of the Lorentz factor is not strongly modified whether radiation can stream through the reconnection layer or not. On the other hand, we show that the width, density and temperature of the reconnection layer are strongly dependent on these assumptions. We then apply the model to the gamma-ray burst context and find that photons cannot diffuse efficiently through the reconnection layer below radius r ∆ D ∼ 10 10.5 cm, which is about an order of magnitude below the photospheric radius. Above r ∆ D , the dynamics asymptotes to the solution of the scenario in which radiation can stream through the reconnection layer. As a result, the density of the current sheet increases sharply, providing efficient photon production by the Bremsstrahlung process which could have profound influence on the emerging spectrum. This effect might provide a solution to the soft photon problem in GRBs.

Plasmas in Gamma-Ray Bursts: Particle Acceleration, Magnetic Fields, Radiative Processes and Environments

“…Evolution of the hydrodynamic quantities in these Poynting-flux dominated outflow within the "striped wind" model was considered by several authors [72][73][74][75][76][77][78][79][155][156][157]. The scaling laws of the acceleration can be derived under the ideal MHD limit approximation, which is a good approximation due to the high baryon load [72].…”

“…This rate is model dependent, and in general depends on the rate of magneto-hydrodynamic (MHD) instabilities that destroy the regular structure of the flow [159][160][161][162][163]. Furthermore, the presence of strong radiative field can affect this rate [157]. It should be noted that several PIC simulations predict a nearly universal reconnection rate, of ∼ 0.1c for highly magnetized flows [164][165][166].…”

Prompt gamma-ray burst emission from gradual magnetic dissipation

“…Many studies (Giannios 2008;Zhang & Yan 2011;McKinney & Uzdensky 2012;Sironi et al 2015;Beniamini & Granot 2016;Granot 2016;Kagan et al 2016;Bégué et al 2017) have therefore recently considered reconnection models as strong candidates for reproducing the prompt sub-MeV emission. In MHD jets, the energy dissipation through reconnection occurs gradually over a wide range of radii (Drenkhahn 2002).…”

Magnetic versus baryonic jets for gamma-ray bursts.

“…If the striped wind has been extensively studied in the context of pulsar [19,20], the effects of radiation have been neglected, but they are expected to be important in the context of GRBs. A detailed derivation of the dynamics can be found in [21], in which the effect of radiation on the striped wind are studied. Here, we present only the results.…”

“…I also discussed photon production mechanisms in this context, showing that Bremsstrahlung remains efficient almost up to the photosphere, which could provide a solution to the photon starvation problem in photospheric emission model for GRBs. The full derivation of the results can be found in [21].…”