192 research outputs found
Explosive Nucleosynthesis from GRB and Hypernova Progenitors: Direct Collapse versus Fallback
The collapsar engine behind long-duration gamma-ray bursts extracts the
energy released from the rapid accretion of a collapsing star onto a
stellar-massed black hole. In a collapsing star, this black hole can form in
two ways: the direct collapse of the stellar core into a black hole and the
delayed collapse of a black hole caused by fallback in a weak supernova
explosion. In the case of a delayed-collapse black hole, the strong
collapsar-driven explosion overtakes the weak supernova explosion before shock
breakout, and it is very difficult to distinguish this black hole formation
scenario from the direct collapse scenario. However, the delayed-collapse
mechanism, with its double explosion, produces explosive nucleosynthetic yields
that are very different from the direct collapse scenario. We present
1-dimensional studies of the nucleosynthetic yields from both black hole
formation scenarios, deriving differences and trends in their nucleosynthetic
yields.Comment: 47 pages, submitted to Ap
Infrared emission from kilonovae: the case of the nearby short hard burst GRB 160821B
We present constraints on Ks-band emission from one of the nearest short hard
gamma-ray bursts, GRB 160821B, at z=0.16, at three epochs. We detect a reddened
relativistic afterglow from the jetted emission in the first epoch but do not
detect any excess kilonova emission in the second two epochs. We compare upper
limits obtained with Keck I/MOSFIRE to multi-dimensional radiative transfer
models of kilonovae, that employ composition-dependent nuclear heating and LTE
opacities of heavy elements. We discuss eight models that combine toroidal
dynamical ejecta and two types of wind and one model with dynamical ejecta
only. We also discuss simple, empirical scaling laws of predicted emission as a
function of ejecta mass and ejecta velocity. Our limits for GRB 160821B
constrain the ejecta mass to be lower than 0.03 Msun for velocities greater
than 0.1c. At the distance sensitivity range of advanced LIGO, similar
ground-based observations would be sufficiently sensitive to the full range of
predicted model emission including models with only dynamical ejecta. The color
evolution of these models shows that I-K color spans 7--16 mag, which suggests
that even relatively shallow infrared searches for kilonovae could be as
constraining as optical searches.Comment: Accepted for Publication in Astrophysical Journal Letter
A Case Study of Small Scale Structure Formation in 3D Supernova Simulations
It is suggested in observations of supernova remnants that a number of large-
and small-scale structures form at various points in the explosion.
Multidimensional modeling of core-collapse supernovae has been undertaken since
SN1987A, and both simulations and observations suggest/show that
Rayleigh-Taylor instabilities during the explosion is a main driver for the
formation of structure in the remnants.
We present a case study of structure formation in 3D in a \msol{15} supernova
for different parameters. We investigate the effect of moderate asymmetries and
different resolutions of the formation and morphology of the RT unstable
region, and take first steps at determining typical physical quantities (size,
composition) of arising clumps. We find that in this progenitor the major RT
unstable region develops at the He/OC interface for all cases considered. The
RT instabilities result in clumps that are overdense by 1-2 orders of magnitude
with respect to the ambient gas, have size scales on the level of a few % of
the remnant diameter, and are not diffused after the first yrs of the
remnant evolution, in the absence of a surrounding medium.Comment: 59 pages, 34 figure
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