We describe a new hybrid framework to model non-thermal spectral signatures from highly energetic particles embedded in a large-scale classical or relativistic magnetohydrodynamic (MHD) flow. Our ...method makes use of Lagrangian particles moving through an Eulerian grid where the (relativistic) MHD equations are solved concurrently. Lagrangian particles follow fluid streamlines and represent ensembles of (real) relativistic particles with a finite energy distribution. The spectral distribution of each particle is updated in time by solving the relativistic cosmic ray transport equation based on local fluid conditions. This enables us to account for a number of physical processes, such as adiabatic expansion, synchrotron and inverse Compton emission. An accurate semi-analytically numerical scheme that combines the method of characteristics with a Lagrangian discretization in the energy coordinate is described. In the presence of (relativistic) magnetized shocks, a novel approach to consistently model particle energization due to diffusive shock acceleration is presented. Our approach relies on a refined shock-detection algorithm and updates the particle energy distribution based on the shock compression ratio, magnetic field orientation, and amount of (parameterized) turbulence. The evolved distribution from each Lagrangian particle is further used to produce observational signatures like emission maps and polarization signals, accounting for proper relativistic corrections. We further demonstrate the validity of this hybrid framework using standard numerical benchmarks and evaluate the applicability of such a tool to study high-energy emission from extragalactic jets.
ABSTRACT
We have performed magnetohydrodynamic (MHD) simulations of relativistic jets from supermassive blackholes over a few tens of kpc for a range of jet parameters. One of the primary aims was to ...investigate the effect of different MHD instabilities on the jet dynamics and their dependence on the choice of jet parameters. We find that two dominant MHD instabilities affect the dynamics of the jet, small-scale Kelvin–Helmholtz (KH) modes and large-scale kink modes, whose evolution depends on internal jet parameters like the Lorentz factor, the ratio of the density and pressure to the external medium, and the magnetization and hence consequently on the jet power. Low power jets are susceptible to both instabilities, kink modes for jets with higher central magnetic field and KH modes for lower magnetization. Moderate power jets do not show appreciable growth of kink modes, but KH modes develop for lower magnetization. Higher power jets are generally stable to both instabilities. Such instabilities decelerate and decollimate the jet while inducing turbulence in the cocoon, with consequences on the magnetic field structure. We model the dynamics of the jets following a generalized treatment of the Begelman–Cioffi relations, which we present here. We find that the dynamics of stable jets match well with simplified analytic models of expansion of non-self-similar FRII jets, whereas jets with prominent MHD instabilities show a nearly self-similar evolution of the morphology as the energy is more evenly distributed between the jet head and the cocoon.
Aims.
In recent years, sub-millimeter (mm) observations of protoplanetary disks have revealed an incredible diversity of substructures in the dust emission. An important result was the finding that ...dust grains of mm size are embedded in very thin dusty disks. This implies that the dust mass fraction in the midplane becomes comparable to that of the gas, increasing the importance of the interaction between the two components there.
Methods.
We use numerical 2.5D simulations to study the interaction between gas and dust in fully globally stratified disks. To this end, we employ the recently developed dust grain module of the PLUTO code. Our model focuses on a typical T Tauri disk model, simulating a short patch of the disk at 10 au which includes grains of a constant Stokes number of
St
= 0.01 and
St
= 0.1, corresponding to grains with sizes of 0.9 cm and 0.9 mm, respectively, for the given disk model.
Results.
By injecting a constant pebble flux at the outer domain, the system reaches a quasi-steady state of turbulence and dust concentrations driven by the streaming instability. For our given setup, and using resolutions up to 2500 cells per scale height, we resolve the streaming instability that leads to local dust clumping and concentrations. Our results show dust density values of around 10–100 times the gas density with a steady-state pebble flux of between 3.5 × 10
−4
and 2.5 × 10
−3
M
Earth
yr
−1
for the models with
St
= 0.01 and
St
= 0.1.
Conclusions.
Grain size and pebble flux for model
St
= 0.01 compare well with dust evolution models of the first million years of disk evolution. For those grains, the scatter opacity dominates the extinction coefficient at mm wavelengths. These types of global dust and gas simulations are a promising tool for studies of the gas and dust evolution at pressure bumps in protoplanetary disks.
A Self-gravity Module for the PLUTO Code Mandal, Ankush; Mukherjee, Dipanjan; Mignone, Andrea
The Astrophysical journal. Supplement series,
09/2023, Letnik:
268, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
We present a novel implementation of an iterative solver for the solution of Poisson’s equation in the PLUTO code for astrophysical fluid dynamics. Our solver relies on a relaxation method ...in which convergence is sought as the steady-state solution of a parabolic equation, whose time discretization is governed by the Runge–Kutta–Legendre (RKL) method. Our findings indicate that the RKL-based Poisson solver, which is both fully parallel and rapidly convergent, has the potential to serve as a practical alternative to conventional iterative solvers such as the Gauss–Seidel and successive overrelaxation methods. Additionally, it can mitigate some of the drawbacks of these traditional techniques. We incorporate our algorithm into a multigrid solver to provide a simple and efficient gravity solver that can be used to obtain the gravitational potentials in self-gravitational hydrodynamics. We test our implementation against a broad range of standard self-gravitating astrophysical problems designed to examine different aspects of the code. We demonstrate that the results match excellently with analytical predictions (when available), and the findings of similar previous studies.
Astrophysical fluid flow studies often encompass a wide range of physical processes to account for the complexity of the system under consideration. In addition to gravity, a proper treatment of ...thermodynamic processes via continuum radiation transport and/or photoionization is becoming the state of the art. We present a major update of our continuum radiation transport module, Makemake, and a newly developed module for photoionization, Sedna, coupled to the magnetohydrodynamics code PLUTO. These extensions are currently not publicly available; access can be granted on a case-by-case basis. We explain the theoretical background of the equations solved, elaborate on the numerical layout, and present a comprehensive test suite for radiation-ionization hydrodynamics. The grid-based radiation and ionization modules support static one-dimensional, two-dimensional, and three-dimensional grids in Cartesian, cylindrical, and spherical coordinates. Each module splits the radiation field into two components, one originating directly from a point source-solved using a ray-tracing scheme-and a diffuse component-solved with a three-dimensional flux-limited diffusion (FLD) solver. The FLD solver for the continuum radiation transport makes use of either the equilibrium one-temperature approach or the linearization two-temperature approach. The FLD solver for the photoionization module enables accounting for the temporal evolution of the radiation field from direct recombination of free electrons into hydrogen's ground state as an alternative to on-the-spot approximation. A brief overview of completed and ongoing scientific studies is given to explicitly illustrate the multipurpose nature of the numerical framework presented.
ABSTRACT
The multimessenger event GW170817/GRB 170817A confirmed that binary neutron star (BNS) mergers can produce short gamma-ray burst (SGRB) jets. This evidence promoted new investigations on the ...mechanisms through which a BNS merger remnant can launch such a powerful relativistic outflow and on the propagation of the latter across the surrounding post-merger environment. In particular, great strides have been made in jet propagation models, establishing connections between the initial jet launching conditions, including the incipient jet launching time (with respect to merger) and the injection parameters, and the observable SGRB prompt and afterglow emission. However, present semi-analytical models and numerical simulations (with one notable exception) adopt simple handmade prescriptions to account for the post-merger environment, lacking a direct association with any specific merging BNS system. Here, we present the first three-dimensional relativistic hydrodynamics simulations of incipient SGRB jets propagating through a post-merger environment that is directly imported from the outcome of a previous general relativistic BNS merger simulation. Our results show that the evolution and final properties of the jet can be largely affected by the anisotropies and the deviations from axisymmetry and homologous expansion characterizing more realistic BNS merger environments. In addition, we find that the inclusion of the gravitational pull from the central compact object, often overlooked, can have a major impact. Finally, we consider different jet launching times referred to the same BNS merger model and discuss the consequences for the ultimate jet properties.
We investigate the onset of pressure-driven toroidal-mode instabilities in accretion mounds on neutron stars by 3D magnetohydrodynamic (MHD) simulations using the pluto MHD code. Our results confirm ...that for mounds beyond a threshold mass, instabilities form finger-like channels at the periphery, resulting in mass-loss from the magnetically confined mound. Ring-like mounds with hollow interior show the instabilities at the inner edge as well. We perform the simulations for mounds of different sizes to investigate the effect of the mound mass on the growth rate of the instabilities. We also investigate the effect of such instabilities on observables such as cyclotron resonant scattering features and timing properties of such systems.
HESS J0632+057: hydrodynamics and non-thermal emission Bosch-Ramon, Valentí; Barkov, Maxim V.; Mignone, Andrea ...
Monthly notices of the Royal Astronomical Society. Letters,
10/2017, Letnik:
471, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract HESS J0632+057 is an eccentric gamma-ray Be binary that produces non-thermal radio, X-rays, GeV and very high-energy gamma-rays. The non-thermal emission of HESS J0632+057 is modulated with ...the orbital period, with a dominant maximum before apastron passage. The nature of the compact object in HESS J0632+057 is not known, although it has been proposed to be a young pulsar as in PSR B1259–63, the only gamma-ray emitting high-mass binary known to host a non-accreting pulsar. In this letter, we present hydrodynamical simulations of HESS J0632+057 in the context of a pulsar and a stellar wind interacting in an eccentric binary, and propose a scenario for the non-thermal phenomenology of the source. In this scenario, the non-thermal activity before and around apastron is linked to the accumulation of non-thermal particles in the vicinity of the binary, and the sudden drop of the emission before apastron is produced by the disruption of the two-wind interaction structure, allowing these particles to escape efficiently. In addition to providing a framework to explain the non-thermal phenomenology of the source, this scenario predicts extended, moving X-ray emitting structures similar to those observed in PSR B1259–63.
We have performed stability analysis of axisymmetric accretion mounds on neutron stars in high-mass X-ray binaries by 2D magnetohydrodynamic (MHD) simulations with the pluto MHD code. We find that ...the mounds are stable with respect to interchange instabilities, but the addition of excess mass destabilizes the equilibria. Our simulations confirm that accretion mounds are unstable with respect to MHD instabilities beyond a threshold mass. We investigate both filled and hollow mounds and for the latter also compute the expected profile of cyclotron resonance scattering features (CRSF). In comparison to the CRSF from filled mounds reported in our earlier work, hollow mounds display wider and more complex line profiles.
The reconstruction of plasma parameters in the interplanetary medium is very important to understand the interplanetary propagation of solar eruptions and for Space Weather application purposes. ...Because only a few spacecraft are measuring in situ these parameters, reconstructions are currently performed by running complex numerical Magneto-hydrodynamic (MHD) simulations starting from remote sensing observations of the Sun. Current models apply full 3D MHD simulations of the corona or extrapolations of photospheric magnetic fields combined with semi-empirical relationships to derive the plasma parameters on a sphere centered on the Sun (inner boundary). The plasma is then propagated in the interplanetary medium up to the Earth’s orbit and beyond. Nevertheless, this approach requires significant theoretical and computational efforts, and the results are only in partial agreement with the in situ observations. In this paper we describe a new approach to this problem called RIMAP – Reverse In situ data and MHD APproach. The plasma parameters in the inner boundary at 0.1 AU are derived directly from the in situ measurements acquired at 1 AU, by applying a back reconstruction technique to remap them into the inner heliosphere. This remapping is done by using the Weber and Davies solar wind theoretical model to reconstruct the wind flowlines. The plasma is then re-propagated outward from 0.1 AU by running a MHD numerical simulation based on the PLUTO code. The interplanetary spiral reconstructions obtained with RIMAP are not only in a much better agreement with the in situ observations, but are also including many more small-scale longitudinal features in the plasma parameters that are not reproduced with the approaches developed so far.
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