111 research outputs found
The Light Curve of Supernova 1987A: The Structure of the Presupernova and Radioactive Nickel Mixing
We have studied the influence of the presupernova structure and the degree of
Ni-56 mixing on the bolometric light curve of SN 1987A in terms of radiation
hydrodynamics in the one-group approximation by abandoning LTE and by taking
into account nonthermal ionization and the contribution of spectral lines to
opacity. Our study shows that moderate Ni-56 mixing at velocities of < 2500
km/s can explain the observed light curve if the density of the outer layers of
the presupernova exceeds the value obtained in the evolutionary model of a
single nonrotating star severalfold. Abandoning LTE and allowing for nonthermal
ionization when solving the equation of state and calculating the mean
opacities and the thermal emission coefficient leads to a significant
difference between the gas temperature and the radiation temperature in the
optically thin layers of the supernova envelope. We demonstrate the fundamental
role of the contribution of spectral lines to the opacity in an expanding
envelope and of the accurate description of radiative transfer in reproducing
the observed shape of the bolometric light curve. We have found that
disregarding the contribution of spectral lines to the opacity introduces an
error of 20% into the explosion energy, and that a similar error is possible
when determining the mass of the ejected matter. The resonant scattering of
radiation in numerous lines accelerates the outer layers to velocities of 36
000 km/s; this additional acceleration affects the outer layers with a mass of
10^{-6} Msun. Proper calculations of the supernova luminosity require that not
only the delay effects, but also the limb-darkening effects be taken into
account.Comment: 16 pages, 13 figures, 1 tabl
Luminous type IIP SN 2013ej with high-velocity Ni-56 ejecta
We explore the well-observed type IIP SN 2013ej with peculiar luminosity
evolution. It is found that the hydrodynamic model cannot reproduce in detail
the bolometric luminosity at both the plateau and the radioactive tail. Yet the
ejecta mass of 23-26 Msun and the kinetic energy of (1.2-1.4)x10^51 erg are
determined rather confidently. We suggest that the controversy revealed in
hydrodynamic simulations stems from the strong asphericity of the Ni-56 ejecta.
An analysis of the asymmetric nebular H-alpha line and of the peculiar
radioactive tail made it possible to recover parameters of the asymmetric
bipolar Ni-56 ejecta with the heavier jet residing in the rear hemisphere. The
inferred Ni-56 mass is 0.039 Msun, twice as large compared to a straightforward
estimate from the bolometric luminosity at the early radioactive tail. The bulk
of ejected Ni-56 has velocities in the range of 4000-6500 km/s. The linear
polarization predicted by the model with the asymmetric ionization produced by
bipolar Ni-56 ejecta is consistent with the observational value.Comment: 7 pages, 8 figures, 3 tables. Accepted for publication in MNRA
Type IIP supernova 2008in: the explosion of a normal red supergiant
The explosion energy and the ejecta mass of a type IIP supernova make up the
basis for the theory of explosion mechanism. So far, these parameters have only
been determined for seven events. Type IIP supernova 2008in is another
well-observed event for which a detailed hydrodynamic modeling can be used to
derive the supernova parameters. Hydrodynamic modeling was employed to describe
the bolometric light curve and the expansion velocities at the photosphere
level. A time-dependent model for hydrogen ionization and excitation was
applied to model the Halpha and Hbeta line profiles. We found an ejecta mass of
13.6 Msun, an explosion energy of 5.05x10^50 erg, a presupernova radius of 570
Rsun, and a radioactive Ni-56 mass of 0.015 Msun. The estimated progenitor mass
is 15.5 Msun. We uncovered a problem of the Halpha and Hbeta description at the
early phase, which cannot be resolved within a spherically symmetric model. The
presupernova of SN 2008in was a normal red supergiant with the minimum mass of
the progenitor among eight type IIP supernovae explored by means of the
hydrodynamic modeling. The problem of the absence of type IIP supernovae with
the progenitor masses <15 Msun in this sample remains open.Comment: 6 pages, 8 figures, 1 table, accepted for publication in A&
Strong effects of time-dependent ionization in early SN 1987A
We study a time-dependent hydrogen ionization in the atmosphere of SN 1987A
during the first month after the explosion. The model includes kinetics of
hydrogen ionization and excitation, molecular hydrogen kinetics, and a
time-dependent energy balance. The primary strong effect of the time-dependent
ionization is the enhanced hydrogen ionization compared to the steady-state
model. The time-dependent ionization provides a sufficient population of
excited hydrogen levels to account for the observed H-alpha without invoking
the external Ni-56. We find that the Ba II 6142 A line in SN 1987A can be
reproduced for the LMC barium abundance. This resolves the long-standing
problem of the unacceptably high barium overabundance in SN 1987A. The key
missing factor that should be blamed for the "barium problem" is the
time-dependent ionization. The modelling of the H-alpha profile on day 4.64
indicates the ratio of the kinetic energy to the ejected mass about 0.83
10^{50} erg/Msun.Comment: 13 pages, 9 figures, 5 tables, submitted to A&
An optimal hydrodynamic model for the normal Type IIP supernova 1999em
There is still no consensus about progenitor masses of Type IIP supernovae.
We study a normal Type IIP SN 1999em in detail and compare it to a peculiar
Type IIP SN 1987A. We computed the hydrodynamic and time-dependent atmosphere
models interpreting simultaneously both the photometric and spectroscopic
observations. The bolometric light curve of SN 1999em and the spectral
evolution of its H-alpha line are consistent with a presupernova radius of 500
Rsun, an ejecta mass of 19.0 Msun, an explosion energy of 1.3x10^51 erg, and a
radioactive 56Ni mass of 0.036 Msun. A mutual mixing of hydrogen-rich and
helium-rich matter in the inner layers of the ejecta guarantees a good fit of
the calculated light curve to that observed. Based on the hydrodynamic models
in the vicinity of the optimal model, we derive the approximate relationships
between the basic physical and observed parameters. We find that the hydrogen
recombination in the atmosphere of a normal Type IIP SN 1999em, as well as most
likely other Type IIP supernovae at the photospheric epoch, is essentially a
time-dependent phenomenon. It is also shown that in normal Type IIP supernovae
the homologous expansion of the ejecta in its atmosphere takes place starting
from nearly the third day after the supernova explosion. A comparison of SN
1999em with SN 1987A reveals two very important results for supernova theory.
First, the comparability of the helium core masses and the explosion energies
implies a unique explosion mechanism for these core collapse supernovae.
Second, the optimal model for SN 1999em is characterized by a weaker 56Ni
mixing up to 660 km/s compared to a moderate 56Ni mixing up to 3000 km/s in SN
1987A, hydrogen being mixed deeply downward to 650 km/s.Comment: 21 pages, 24 figures. Accepted for publication in Astronomy &
Astrophysic
Ejecta and progenitor of the low-luminosity Type IIP supernova 2003Z
The origin of low-luminosity Type IIP supernovae is unclear: they have been
proposed to originate either from massive (about 25 Msun) or low-mass (about 9
Msun) stars. We wish to determine parameters of the low-luminosity Type IIP
supernova 2003Z, to estimate a mass-loss rate of the presupernova, and to
recover a progenitor mass. We compute the hydrodynamic models of the supernova
to describe the light curves and the observed expansion velocities. The wind
density of the presupernova is estimated using a thin shell model for the
interaction with circumstellar matter. We estimate an ejecta mass of 14 Msun,
an explosion energy of 2.45x10^50 erg, a presupernova radius of 229 Rsun, and a
radioactive Ni-56 amount of 0.0063 Msun. The upper limit of the wind density
parameter in the presupernova vicinity is 10^13 g/cm, and the mass lost at the
red/yellow supergiant stage is less than 0.6 Msun assuming the constant
mass-loss rate. The estimated progenitor mass is in the range of 14.4-17.4
Msun. The presupernova of SN 2003Z was probably a yellow supergiant at the time
of the explosion. The progenitor mass of SN 2003Z is lower than those of SN
1987A and SN 1999em, normal Type IIP supernovae, but higher than the lower
limit of stars undergoing a core collapse. We propose an observational test
based on the circumstellar interaction to discriminate between the massive
(about 25 Msun) and moderate-mass (about 16 Msun) scenarios.Comment: 8 pages, 9 figures, 3 tables, accepted for publication in Astronomy &
Astrophysics; one reference remove
Type IIP Supernova 2009kf: Explosion Driven by Black Hole Accretion?
Unusually bright type IIP supernova (SN) 2009kf is studied employing the
hydrodynamic modelling. We derived optimal values of the ejecta mass of 28.1
Msun, explosion energy of 2.2x10^{52} erg, and presupernova radius of 2x10^3
Rsun assuming that Ni-56 mass is equal to the upper limit of 0.4 Msun. We
analyzed effects of the uncertainties in the extinction and Ni-56 mass and
concluded that both the ejecta mass and explosion energy cannot be
significantly reduced compared with the optimal values. The huge explosion
energy of SN 2009kf indicates that the explosion is caused by the same
mechanism which operates in energetic SNe Ibc (hypernovae), i.e., via a rapid
disk accretion onto black hole. The ejecta mass combined with the black hole
mass and the mass lost by stellar wind yields the progenitor mass of about 36
Msun. We propose a scenario in which massive binary evolution might result in
the SN 2009kf event.Comment: 14 pages, 4 figures, 1 table, accepted for publication in ApJ Letter
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