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Comparison of jet-breakout dynamics for the case Lj.5.49.Me.010 (i.e. L jet = 5 × 10 49 erg s −1 and M ej = 0 . 10 M ). The panels in the left column show the rest-mass density, while those in the right column report the distributions of the Lorentz factor. To highlight the contrast among different distributions, the left part of each panel reports the anisotropic distribution of rest-mass density ('off-axis' in the top row and 'on-axis' in the bottom row), while the right part the dynamics across a homogeneous distribution. All panels refer to a time t = 0 . 7 s since the launch of the jet.
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Binary neutron stars mergers widely accepted as potential progenitors of short gamma-ray bursts. After the remnant of the merger has collapsed to a black hole, a jet is powered and may breakout from the the matter expelled during the collision and the subsequent wind emission. The interaction of the jet with the ejecta may affect its dynamics and t...
Contexts in source publication
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... start by studying the effect of the anisotropies in the rest-mass density distribution on the propagation of the jet in the ejecta. Fig. 2 shows a snapshot of the jet-ejecta evolution at the time of the jet breakout for different ejecta density profiles from the Lj.5.49.Me.010 runs (see Table 1 ). In particular, Fig. 2 reports in its left panel the rest-mass density distribution, while on the right panel the distribution of the Lorentz factor (Fig. 3 reports the same ...
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... start by studying the effect of the anisotropies in the rest-mass density distribution on the propagation of the jet in the ejecta. Fig. 2 shows a snapshot of the jet-ejecta evolution at the time of the jet breakout for different ejecta density profiles from the Lj.5.49.Me.010 runs (see Table 1 ). In particular, Fig. 2 reports in its left panel the rest-mass density distribution, while on the right panel the distribution of the Lorentz factor (Fig. 3 reports the same quantities as Fig. 2 but on a scale that highlights the breakout region). For each panel, in addition, the left part refers to a simulation with an anisotropic and inhomogeneous ...
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... 2 shows a snapshot of the jet-ejecta evolution at the time of the jet breakout for different ejecta density profiles from the Lj.5.49.Me.010 runs (see Table 1 ). In particular, Fig. 2 reports in its left panel the rest-mass density distribution, while on the right panel the distribution of the Lorentz factor (Fig. 3 reports the same quantities as Fig. 2 but on a scale that highlights the breakout region). For each panel, in addition, the left part refers to a simulation with an anisotropic and inhomogeneous distribution ('off-axis' on the top row and 'on-axis' on the bottom row), while the right part provides the evolution in the reference case of an isotropic but inhomogeneous ...
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... particular, the acceleration following the interaction with an underdense region along the jet direction are compensated by the deceleration when the jet encounters an o v erdense re gion. As a result, the jet breaks-out almost at the same time as in the case of a propagation across an isotropic ejecta distribution (compare the left and right parts of the bottom-left panel of Figs 2 and 3 ). ...
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... mentioned in the previous section, the propagation of the jet within the ejected envelope leads to a turbulent shear layer that is normally referred to as the 'cocoon' for its peculiar shape. At the breakout time, Figs 2 and 3 illustrate the detailed morphology of the cocoon, which can be readily identified by the steep gradient in density . More precisely , we distinguish the matter in the cocoon from the jet material by following the conditions proposed by Hamidani & Ioka ( 2023 ), that is, we mark as filled with cocoon-matter cells for which the following conditions are met: ∞ ≤ 10, < 5, and | v θ | > 0, where the last criterion is imposed to a v oid the mis-identification of ejected material or interstellar medium (for which | v θ | = 0) with the matter in the cocoon. ...
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... proposed by Hamidani & Ioka ( 2023 ), that is, we mark as filled with cocoon-matter cells for which the following conditions are met: ∞ ≤ 10, < 5, and | v θ | > 0, where the last criterion is imposed to a v oid the mis-identification of ejected material or interstellar medium (for which | v θ | = 0) with the matter in the cocoon. Clearly, Fig. 2 shows that the cocoon varies at different vertical heights and hence it changes during the evolution. More importantly, it is easy to realize that the different geometric properties of the ejected material do have an impact on the morphology of the ...
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... this may appear surprising, it reflects the analogy already remarked between the propagation across homogeneous and on-axis perturbations, where the sequence of o v er -and under -densities along the jet path compensate and cancel out, hence giving a very similar cocoon and breakout time as in the homogeneous case (cf. Figs 2 and 3 ). The right panel of Fig. 6 , on the other hand, shows E coc as a function of the two main parameters of our setup, i.e. ...
Citations
... For BNS mergers, the picture for fallback material is somewhat complicated by the presence of various ejecta (that are either dynamical or secular; Gill et al. 2019), the nature of the remnant compact object (which can be either a massive neutron star or a black hole; Nathanail et al. 2021b), and the interaction of the jet with the ejected material (Murguia-Berthier et al. 2016;Hamidani et al. 2020;Urrutia et al. 2021;Nathanail et al. 2021a;Gottlieb et al. 2022;Kiuchi et al. 2023;Mpisketzis et al. 2024). Recently, Metzger & Fernández (2021) and Ishizaki et al. (2021a) have sought to explain the putative excess in the afterglow of GW170817 with the emission of fallback material from the secular ejecta. ...
... The separatrix between the trapped and the escaping fallback radiation will depend on a number of factors, such as the physical separation between the bound and unbound flows, the opening of the jet cavity, the hydrodynamical properties of the ejecta and its degree of anisotropy, and the size and density of the cocoon. Overall, simulations show that the angular size of the cocoon is small (Hamidani & Ioka 2021), such that the vast majority of the ejecta is unperturbed by the passing of the jet and should follow the description of Section 3, especially for very luminous jets that successfully break out from the ejecta (Duffell et al. 2018;Mpisketzis et al. 2024). ...
Using a set of general-relativistic magnetohydrodynamics simulations that include proper neutrino transfer, we assess for the first time the role played by the fallback accretion onto the remnant from a binary neutron star merger over a timescale of hundreds of seconds. In particular, we find that, independently of the equation of state, the properties of the binary, and the fate of the remnant, the fallback material reaches a total mass of ≳10 ⁻³ M ⊙ , i.e., about 50% of the unbound matter, and that the fallback accretion rate follows a power law in time with slope ∼ t −5/3 . Interestingly, the timescale of the fallback and the corresponding accretion luminosity are in good agreement with the so-called “extended emission” observed in short gamma-ray bursts (GRBs). Using a simple electromagnetic emission model based on the self-consistent thermodynamical state of the fallback material heated by r -process nucleosynthesis, we show that this fallback material can shine in gamma and X-rays with luminosities ≳10 ⁴⁸ erg s ⁻¹ for hundreds of seconds, thus making it a good and natural candidate to explain the extended emission in short GRBs. Additionally, our model for fallback emission reproduces well and rather naturally some of the phenomenological traits of extended emission, such as its softer spectra with respect to the prompt emission and the presence of exponential cutoffs in time. Our results clearly highlight that fallback flows onto merger remnants cannot be neglected, and the corresponding emission represents a very promising and largely unexplored avenue to explain the complex phenomenology of GRBs.
... The first is to assume as a spherical wind expanding homologously and parametrized by its mass loss rateṀ wind and velocity (Murguia-Berthier et al. 2014;Hamidani et al. 2020;Urrutia et al. 2021;Nativi et al. 2022;Hamidani & Ioka 2023;Mpisketzis et al. 2024). Alternatively, the wind can also be described by homologous toroidal winds, whose angular profiles of density ρ wind (r, θ) and velocity v wind (r, θ) were extracted from neutrino driven or strongly magnetized winds (Aloy et al. 2005;Nativi et al. 2020;Murguia-Berthier et al. 2021). ...
... An important application of the jet and cocoon evolution at large scales involves extrapolating energy distributions to distances of r ∼ 10 16 cm, to estimate the afterglow radiation (e.g., Duffell et al. 2018;Lazzati et al. 2018;Mooley et al. 2018;Nathanail et al. 2020;Urrutia et al. 2021;Nativi et al. 2022;Mpisketzis et al. 2024). Our results suggest the necessity of modifying energy distribution at these large scales, where the transformation from thermal to kinetic energy becomes signifi-cant. ...
Short Gamma-Ray Bursts (GRBs) are often associated with NSNS or BHNS mergers. The discovery of GW/GRB 170817A has enhanced our understanding, revealing that the interaction between relativistic jets and post-merger outflows influences the observed radiation. However, the nature of compact binary merger event suggests that the system can be more complex than the uniform jet interacting with a homologously expanding wind. We consider here an improved scenario by performing a set of two-dimensional, large scale numerical simulations, and we investigate the interaction between short GRB jets and post-merger disk wind outflows. We focus on two types of configurations, arising from NSNS and BHNS mergers. The simulations consider the effects of the r-process nucleosynthesis in the accretion disk wind on its pressure profile. The main properties of the jet, such as its energy distribution and collimation degree, are estimated from our simulations. We found that a) the impact of the r-process on initial wind pressure leads to significant changes in the jet collimation and cocoon expansion; b) the angular structure of thermal and kinetic energy components in the jets, cocoons, and winds differ with respect to simple homologous models, hence it would affect the predictions of GRB afterglow emission; c) the temporal evolution of the structure reveals conversion of thermal to kinetic energy being different for each component in the system (jet, cocoon, and wind); d) post-merger environments influence energy structure and material dispersion, altering the interaction between jets and disk winds.
