557 research outputs found
Circumstellar interaction of the type Ia supernova 2002ic
We propose a model to account for the bolometric light curve, quasi-continuum
and the Ca II emission features of the peculiar type Ia supernova (SN) 2002ic,
which exploded in a dense circumstellar envelope. The model suggests that the
SN Ia had the maximum possible kinetic energy and that the ejecta expand in an
approximately spherically symmetric (possibly clumpy) circumstellar
environment. The Ca II and quasi-continuum are emitted by shocked SN ejecta
that underwent deformation and fragmentation in the intershock layer. Modeling
of the Ca II triplet implies that the contribution of the O I 8446 A line is
about 25% of the 8500 A feature on day 234, which permits us to recover the
flux in the Ca II 8579 A triplet from the flux of 8500 A blend reported by Deng
et al. (2004). We use the Ca II doublet and triplet fluxes on day 234 to derive
the electron temperature (~4400 K) in the Ca II line-emitting zone and the
ratio of the total area of dense fragments to the area of the shell, S/S_0 ~
100. We argue that Ca II bands and quasi-continuum originate from different
zones of the shocked ejecta that reflect the abundance stratification of the
supernova.Comment: 12 pages, MNRAS, in pres
Pulsar spins from an instability in the accretion shock of supernovae
Rotation-powered radio pulsars are born with inferred initial rotation
periods of order 300 ms (some as short as 20 ms) in core-collapse supernovae.
In the traditional picture, this fast rotation is the result of conservation of
angular momentum during the collapse of a rotating stellar core. This leads to
the inevitable conclusion that pulsar spin is directly correlated with the
rotation of the progenitor star. So far, however, stellar theory has not been
able to explain the distribution of pulsar spins, suggesting that the birth
rotation is either too slow or too fast. Here we report a robust instability of
the stalled accretion shock in core-collapse supernovae that is able to
generate a strong rotational flow in the vicinity of the accreting
proto-neutron star. Sufficient angular momentum is deposited on the
proto-neutron star to generate a final spin period consistent with
observations, even beginning with spherically symmetrical initial conditions.
This provides a new mechanism for the generation of neutron star spin and
weakens, if not breaks, the assumed correlation between the rotational periods
of supernova progenitor cores and pulsar spin.Comment: To be published in Natur
PHotometry Assisted Spectral Extraction (PHASE) and identification of SNLS supernovae
Aim: We present new extraction and identification techniques for supernova
(SN) spectra developed within the Supernova Legacy Survey (SNLS) collaboration.
Method: The new spectral extraction method takes full advantage of
photometric information from the Canada-France-Hawai telescope (CFHT) discovery
and reference images by tracing the exact position of the supernova and the
host signals on the spectrogram. When present, the host spatial profile is
measured on deep multi-band reference images and is used to model the host
contribution to the full (supernova + host) signal. The supernova is modelled
as a Gaussian function of width equal to the seeing. A chi-square minimisation
provides the flux of each component in each pixel of the 2D spectrogram. For a
host-supernova separation greater than <~ 1 pixel, the two components are
recovered separately and we do not use a spectral template in contrast to more
standard analyses. This new procedure permits a clean extraction of the
supernova separately from the host in about 70% of the 3rd year ESO/VLT spectra
of the SNLS. A new supernova identification method is also proposed. It uses
the SALT2 spectrophotometric template to combine the photometric and spectral
data. A galaxy template is allowed for spectra for which a separate extraction
of the supernova and the host was not possible.
Result: These new techniques have been tested against more standard
extraction and identification procedures. They permit a secure type and
redshift determination in about 80% of cases. The present paper illustrates
their performances on a few sample spectra.Comment: 27 pages, 18 Figures, 1 Table. Accepted for publication in A&
Advancing Nucleosynthesis in Self-consistent, Multidimensional Models of Core-Collapse Supernovae
We investigate core-collapse supernova (CCSN) nucleosynthesis in polar
axisymmetric simulations using the multidimensional radiation hydrodynamics
code CHIMERA. Computational costs have traditionally constrained the evolution
of the nuclear composition in CCSN models to, at best, a 14-species
-network. Such a simplified network limits the ability to accurately
evolve detailed composition, neutronization and the nuclear energy generation
rate. Lagrangian tracer particles are commonly used to extend the nuclear
network evolution by incorporating more realistic networks in post-processing
nucleosynthesis calculations. Limitations such as poor spatial resolution of
the tracer particles, estimation of the expansion timescales, and determination
of the "mass-cut" at the end of the simulation impose uncertainties inherent to
this approach. We present a detailed analysis of the impact of these
uncertainties on post-processing nucleosynthesis calculations and implications
for future models.Comment: Proceedings of the 13th Symposium on Nuclei in the Cosmos. 7-11 July
2014. Debrecen, Hungar
An Optimal Algorithm for Tiling the Plane with a Translated Polyomino
We give a -time algorithm for determining whether translations of a
polyomino with edges can tile the plane. The algorithm is also a
-time algorithm for enumerating all such tilings that are also regular,
and we prove that at most such tilings exist.Comment: In proceedings of ISAAC 201
Simulating fast time variations in the supernova neutrino flux in Hyper-Kamiokande
Hyper-Kamiokande is a proposed next-generation water Cherenkov detector. If a galactic supernova happens, it will deliver a high event rate ( neutrino events in total) as well as event-by-event energy information. Recent supernova simulations exhibit the Standing Accretion Shock Instability (SASI) which causes oscillations in the number flux and mean energy of neutrinos. The amplitude of these oscillations is energy-dependent, so the energy information available in Hyper-Kamiokande could be used to improve the detection prospects of these SASI oscillations. To determine whether this can be achieved in the presence of detector effects like backgrounds and finite energy uncertainty, we have started work on a detailed simulation of Hyper-Kamiokande's response to a supernova neutrino burst
Properties of the ultraviolet flux of type Ia supernovae: an analysis with synthetic spectra of SN 2001ep and SN 2001eh
The spectral properties of type Ia supernovae in the ultraviolet (UV) are
investigated using the early-time spectra of SN 2001ep and SN 2001eh obtained
using the Hubble Space Telescope (HST). A series of spectral models is computed
with a Monte Carlo spectral synthesis code, and the dependence of the UV flux
on the elemental abundances and the density gradient in the outer layers of the
ejecta is tested. A large fraction of the UV flux is formed by reverse
fluorescence scattering of photons from red to blue wavelengths. This process,
combined with ionization shifts due to enhanced line blocking, can lead to a
stronger UV flux as the iron-group abundance in the outer layers is increased,
contrary to previous claims.Comment: 14 pages, 13 figures. Replaced with revised version accepted for
publication in MNRA
VLBI Observations of SN 2008D
We report on two epochs of very-long-baseline interferometry (VLBI)
observations of the Type Ib/c supernova SN 2008D, which was associated with the
X-ray outburst XRF 080109. At our first epoch, at t = 30 days after the
explosion, we observed at 22 and 8.4 GHz, and at our second, at t = 133 days,
at 8.4 and 5.0 GHz. The VLBI observations allow us to accurately measure the
source's size and position at each epoch, and thus constrain its expansion
velocity and proper motion. We find the source at best marginally resolved at
both epochs, allowing us to place a 3sigma upper limit of ~0.75c on the
expansion velocity of a circular source. For an elongated source, our
measurements are compatible with mildly relativistic expansion. However, our
3sigma upper limit on the proper motion is 4 micro-arcsec/day, corresponding to
an apparent velocity of <0.6c, and is consistent with a stationary flux
centroid. This limit rules out a relativistic jet such as an gamma-ray burst
jet away from the line of sight, which would be expected to show apparent
proper motion of >c. Taken together, our measurements argue against the
presence of any long-lived relativistic outflow in SN 2008D. On the other hand,
our measurements are consistent with the nonrelativistic expansion velocities
of <30,000 km/s and small proper motions (<500 km/s) seen in typical
supernovae.Comment: Accepted for publication in the Astrophysical Journal Letter
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