3 research outputs found
Towards inferring the geometry of kilonovae
Recent analysis of the kilonova, AT2017gfo, has indicated that this event was
highly spherical. This may challenge hydrodynamics simulations of binary
neutron star mergers, which usually predict a range of asymmetries, and
radiative transfer simulations show a strong direction dependence. Here we
investigate whether the synthetic spectra from a 3D kilonova simulation of
asymmetric ejecta from a hydrodynamical merger simulation can be compatible
with the observational constraints suggesting a high degree of sphericity in
AT2017gfo. Specifically, we determine whether fitting a simple P-Cygni line
profile model leads to a value for the photospheric velocity that is consistent
with the value obtained from the expanding photosphere method. We would infer
that our kilonova simulation is highly spherical at early times, when the
spectra resemble a blackbody distribution. The two independently inferred
photospheric velocities can be very similar, implying a high degree of
sphericity, which can be as spherical as inferred for AT2017gfo, demonstrating
that the photosphere can appear spherical even for asymmetrical ejecta. The
last-interaction velocities of radiation escaping the simulation show a high
degree of sphericity, supporting the inferred symmetry of the photosphere. We
find that when the synthetic spectra resemble a blackbody the expanding
photosphere method can be used to obtain an accurate luminosity distance
(within 4-7 per cent).Comment: 11 pages, submitted to MNRA
tardis-sn/tardis: TARDIS v2023.11.05
<p>This release has been created automatically by the TARDIS continuous delivery pipeline.</p>
<p>A complete list of changes for this release is available at <a href="https://github.com/tardis-sn/tardis/blob/master/CHANGELOG.md">CHANGELOG.md</a>.</p>
tardis-sn/tardis: TARDIS v2023.10.20
<p>This release has been created automatically by the TARDIS continuous delivery pipeline.</p>
<p>A complete list of changes for this release is available at <a href="https://github.com/tardis-sn/tardis/blob/master/CHANGELOG.md">CHANGELOG.md</a>.</p>