214 research outputs found
Off-axis synchrotron light curves from full-time-domain moving-mesh simulations of jets from massive stars
We present full-time-domain, moving-mesh, relativistic hydrodynamic
simulations of jets launched from the center of a massive progenitor star and
compute the resulting synchrotron light curves for observers at a range of
viewing angles. We follow jet evolution from ignition inside the stellar
center, propagation in the stellar envelope and breakout from the stellar
surface, then through the coasting and deceleration phases. The jet compresses
into a thin shell, sweeps up the circumstellar medium, and eventually enters
the Newtonian phase. The jets naturally develop angular and radial structure
due to hydro-dynamical interaction with surrounding gas. The calculated
synchrotron light curves cover the observed temporal range of prompt to late
afterglow phases of long gamma-ray bursts (LGRBs). The on-axis light curves
exhibit an early emission pulse originating in shock-heated stellar material,
followed by a shallow decay and a later steeper decay. The off-axis light
curves rise earlier than previously expected for top-hat jet models -- on a
time scale of seconds to minutes after jet breakout, and decay afterwards.
Sometimes the off-axis light curves have later re-brightening components that
can be contemporaneous with SNe Ic-bl emission. Our calculations may shed light
on the structure of GRB outflows in the afterglow stage. The off-axis light
curves from full-time-domain simulations advocate new light curve templates for
the search of off-axis/orphan afterglows
High-Frequency Voronoi Noise Reduced by Smoothed Mesh Motion
We describe a technique for improving the performance of hydrodynamics codes
which employ a moving Voronoi mesh. Currently, such codes are susceptible to
high-frequency noise produced by rapid adjustments in the grid topology on the
smallest scales. The treatment for this grid noise is simple; instead of moving
the mesh-generating marker points with the local fluid velocity, this velocity
field is smoothed on small scales, so that neighboring marker points generally
have similar velocities. We demonstrate significant improvement gained by this
adjustment in several code tests relevant to the physics which moving-mesh
codes are designed to capture.Comment: MNRAS Accepte
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