Issue |
A&A
Volume 506, Number 2, November I 2009
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|
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Page(s) | 829 - 834 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/200912273 | |
Published online | 27 August 2009 |
A&A 506, 829-834 (2009)
High mass of the type IIP supernova 2004et inferred from hydrodynamic modeling
V. P. Utrobin1,2 - N. N. Chugai3
1 - Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
2 -
Institute of Theoretical and Experimental Physics, B. Cheremushkinskaya St. 25, 117218 Moscow, Russia
3 -
Institute of Astronomy of Russian Academy of Sciences, Pyatnitskaya St. 48, 109017 Moscow, Russia
Received 3 April 2009 / Accepted 7 July 2009
Abstract
Context. Previous studies of type IIP supernovae have
inferred that progenitor masses recovered from hydrodynamic models are
higher than
.
Aims. To verify the progenitor mass of this supernova category,
we attempt a parameter determination of the well-observed luminous
type IIP supernova 2004et.
Methods. We model the bolometric light curve and the
photospheric velocities of SN 2004et by means of hydrodynamic
simulations in an extended parameter space.
Results. From hydrodynamic simulations and observational data, we infer a presupernova radius of 1500
,
an ejecta mass of 24.5
,
an explosion energy of
1051 erg, and a radioactive 56Ni mass of 0.068
.
The estimated progenitor mass on the main sequence is in the range of
.
In addition, we find clear signatures of the explosion asymmetry in the nebular spectra of SN 2004et.
Conclusions. The measured progenitor mass of SN 2004et is
significantly higher than the progenitor mass suggested by the
pre-explosion images. We speculate that the mass inferred from
hydrodynamic modeling is overestimated and crucial missing factors are
multi-dimensional effects.
Key words: stars: supernovae: individual: SN 2004et - stars: supernovae: general
1 Introduction
The major parameters of core-collapse supernova (SN) are thought to be
linked to the initial stellar mass on the main sequence, the progenitor
mass. However, the genealogy of different varieties of SNe is as yet
poorly known. Fortunately, hydrodynamic modeling of the light curves
and the expansion velocities allows us to estimate SN parameters such
as a pre-SN radius, an ejecta mass, an explosion energy, and a
radioactive 56Ni amount.
In the case of SNe IIP, the mass lost prior to the pre-SN stage is
relatively small for stars with an initial mass less than
,
so the ejecta mass provides us with a reliable estimate of the
progenitor mass or at least its lower limit.
Compared to other core-collapse SNe Ib/c and SNe IIn, we are
able to recover the ejecta mass of SNe IIP from hydrodynamic
modeling with greater confidence because of both an accurate estimation
of the photospheric velocity related to the high opacity of the
hydrogen-rich matter, and a low contribution of the circumstellar
interaction to the SN luminosity.
Hydrodynamic modeling should only be applied to well-observed
SNe IIP. An adequate simulation of the bolometric light curve and
the evolution in the photospheric velocities requires both high-quality
photometric and spectroscopic data (Utrobin 2007).
For the above reason, hydrodynamic simulations of SNe IIP have
been performed for only a handful of events: SN 1987A,
SN 1999em, SN 2003Z, and SN 2005cs. For these particular
cases, the inferred progenitor masses have been found unexpectedly to
be in the range of
(Utrobin & Chugai 2008), well above the median value of
for the Salpeter initial mass distribution in the mass range of
responsible for SNe IIP (Heger et al. 2003), i.e., the progenitor masses are on average more massive than expected.
A more challenging problem is one related to the analysis of the sub-luminous SN 2005cs. The progenitor mass of
inferred from hydrodynamic modeling (Utrobin & Chugai 2008) was found to significantly exceed the progenitor mass of
recovered from archival HST images (Maund et al. 2005; Li et al. 2006; Eldridge et al. 2007). No reasonable explanation of this disparity has been proposed.
To pinpoint the cause of this disagreement between the two methods of the mass determination, one needs to confirm this discrepancy in mass measurements for a larger sample of SNe IIP with a broad range of observational characteristics. In this respect, the well-observed luminous SN 2004et in the nearby galaxy NGC 6946 is a particularly favorable case. This object discovered soon after its explosion has the highest intrinsic luminosity among well-studied events (Sahu et al. 2006) and, perhaps, the highest ejecta mass and explosion energy. In this case, the progenitor was directly identified in the archival images (Li et al. 2005).
Here we perform hydrodynamic modeling of SN 2004et to recover the basic parameters: pre-SN radius, ejecta mass, explosion energy, and radioactive 56Ni mass. A brief description of the hydrodynamic model is given in Sect. 2.1, and the basic parameters of the optimal model are obtained in Sect. 2.2. In Sect. 2.3, we investigate whether the non-evolutionary model should be used instead of evolutionary pre-SN for the one-dimensional hydrodynamic modeling of SN 2004et and in general SNe IIP. The progenitor mass of SN 2004et is evaluated and compared to estimations for other SNe IIP (Sect. 2.4). The measured progenitor mass noticeably exceeds the mass estimated from the pre-explosion images, and this disagreement is discussed in Sect. 3.1. In particular, we propose that the explosion asymmetry could be responsible for the disagreement in mass estimates and explore signatures of the explosion asymmetry in the SN 2004et nebular spectra (Sect. 3.2). Finally, in Sect. 4, we summarize the results obtained.
We adopt a distance to NGC 6946 of 5.5 Mpc and a reddening E(B-V)=0.41 as measured by Li et al. (2005), an explosion date on September 22.0 UT (JD 2 453 270.5), and a recession velocity to the host galaxy of 45 km s-1 following Sahu et al. (2006).
2 Hydrodynamic model and progenitor mass
2.1 Model overview
The modeling of the SN explosion is performed using the
spherically-symmetric hydrodynamic code with one-group radiation
transfer (Utrobin 2004, 2007), which has been applied previously to other SNe IIP. Utrobin (2007) found that both this one-group approach and the multi-group approach of Baklanov et al. (2005)
measured similar ejecta mass and explosion energy for SN 1999em.
The basic equations and details of the input physics, including
calculations of mean opacities, are described in Utrobin (2004).
The present version of the code includes additionally Compton cooling
and heating. The explosion energy is modeled by placing the supersonic
piston close to the outer edge of the 1.6
central core, which is removed from the computational mass domain and
assumed to collapse to become a neutron star. The principal limitation
of the code is that the explosion asymmetry and the Rayleigh-Taylor
mixing between the helium core and hydrogen envelope (Müller
et al. 1991)
cannot be correctly treated by the one-dimensional model. We,
therefore, study a ``non-evolutionary'' pre-SN, which takes into
account the result of the mixing during the explosion and the shock
propagation in the evolutionary pre-SN. The distinctive feature of the
non-evolutionary model is a smoothed density and composition jumps
between the helium core and the hydrogen envelope.
![]() |
Figure 1:
Density distribution as a function of interior mass a) and
radius b) for the optimal pre-SN model. The central core of 1.6 |
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The resultant structure of the non-evolutionary pre-SN in our optimal model is shown in Fig. 1. The pre-SN model is defined to be a red supergiant (RSG) with a radius of
,
three times larger than in the case of the normal type IIP SN 1999em (Utrobin 2007).
This large pre-SN radius for SN 2004et is implied by the broad
initial peak of the bolometric light curve shown by Sahu et al. (2006). The adopted mixing between the helium core and hydrogen envelope in the optimal model is shown in Fig. 2. The degree of mixing determines the light curve at the end of the plateau (Utrobin et al. 2007).
The unmixed helium-core mass adopted for SN 2004et is
,
which corresponds to the final helium core of a main-sequence star of
(Hirschi et al. 2004).
We note that the model light curve is not sensitive to any variation in
the helium-core mass of the mixed model (Utrobin et al. 2007).
![]() |
Figure 2: The mass fraction of hydrogen (solid line), helium (long dashed line), CNO elements (short dashed line), and Fe-peak elements including radioactive 56Ni (dotted line) in the ejecta of the optimal model. |
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2.2 Basic parameters
The search for the best-fit model parameters is performed by
computations of an extensive grid of hydrodynamic models. The optimal
model should reproduce simultaneously the bolometric light curve and
the photospheric velocity evolution in the best way. As a result, we
derive the ejecta mass
,
the explosion energy
1051 erg, the pre-SN radius R0=1500
,
and the 56Ni mass
.
The uncertainties in the basic parameters are calculated by assuming
relative errors in the input observational data: 11% in the distance,
7% in the dust absorption, 5% in the photospheric velocity,
and 2% in the plateau duration. In general, the errors of derived
parameters should be somewhat larger because of model systematic
errors. However, the latter cannot be confidently estimated unless a
more advanced and correct model is developed.
The model uncertainties will be discussed below in Sect. 3.2.
![]() |
Figure 3:
The density and the 56Ni mass fraction as a function of velocity for the optimal model at t=50 days. Dash-dotted line is the density distribution fit
|
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The density distribution in the freely expanding SN envelope is shown in Fig. 3. Multiple shells in the outermost layers with velocities v>14 000 km s-1 (Fig. 3)
form at the shock breakout stage by the radiative acceleration in the
optically thin regime. The origin of these shells is related to the
specific behavior of the line opacity in the outer rarefied layers of
temperature
K. The innermost shell of mass
at the velocity of 11 700 km s-1 is the thin shell formed by the effect of the shock breakout in the optically thick regime (Grassberg et al. 1971; Chevalier 1981).
![]() |
Figure 4:
The calculated bolometric light curve of the optimal model (solid line) overplotted on the bolometric data of SN 2004et evaluated from the |
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The optimal model describes the bolometric light curve quite well, including its initial (t<30 days) peak (Fig. 4). This peak is substantially broader and more luminous than the initial peak of SN 1999em (cf. Sahu et al. 2006).
It is the initial luminosity peak of SN 2004et that requires the
larger radius of the pre-SN model compared to the pre-SN radius of
in the case of SN 1999em (Utrobin 2007).
![]() |
Figure 5: Optimal hydrodynamic model. Panels a)-c): the calculated B, V, and R light curves (solid lines) compared with the corresponding observations of SN 2004et obtained by Sahu et al. (2006) (open circles). Panel d): the calculated photospheric velocity (solid line) is compared with photospheric velocities estimated from the absorption minimum of the Fe II 5169 Å line (open circles) by Sahu et al. (2006) and recovered from the Na I doublet profile (filled circles). |
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With one-group radiation transfer, the hydrodynamic model is not assumed to reproduce the monochromatic light curves in detail. However, it is instructive to compare the model and the observations in B, V, and R bands (Figs. 5a-c). The B light curve is reproduced at the initial hot phase, but not at the late phase. The overall fit of the V light curve is much tighter. In R band, the calculated light curve reproduces the plateau data, but does not describe the very initial stages of the light curve. The differences between the hydrodynamic model and the observations are related to deviations of the SN spectrum from a blackbody. These deviations are significant in the blue and ultraviolet at late photospheric epochs, which explains why the disagreement is strongest in B band.
The computed photospheric velocity is shown together with two sets of observational data (Fig. 5d): the first is recovered from an absorption minimum of the Fe II 5169 Å line (Sahu et al. 2006)
and the second, from our modeling of the Na I doublet
profile.
The latter photospheric velocities can be measured more confidently
than those recovered from absorption minima, especially at late
photospheric epochs when absorption lines become strong.
The model photospheric velocity is consistent with both the
Na I data and the early data of the
Fe II 5169 Å absorption minimum. We also modeled
profiles of the Fe II 4924, 5018, 5169 Å lines at late
photospheric stages, and found that the photospheric velocities
obtained from these lines were rather similar to velocities obtained by
modeling the Na I doublet profile. Unfortunately, the
spectral data of SN 2004et for the early stages are missing. The
blue edge of the H absorption in the earliest spectrum on day 24 implies a maximal expansion velocity of
km s-1 in the ejecta. This velocity is consistent with the model maximal velocity of 12 000 km s-1.
2.3 Explosion of evolutionary presupernova
The arguments in favor of the non-evolutionary pre-SN model leave some doubts and raise a question: why should we not consider an evolutionary pre-SN? This issue has already been explored for the sub-luminous type IIP SN 2005cs (Utrobin & Chugai 2008), for which we found that the evolutionary pre-SN did not allow us to produce a realistic description of both the light curve and the photospheric velocities. A similar problem was encountered while modeling the explosion of evolutionary pre-SNe with other hydrodynamic codes (Chieffi et al. 2003; Woosley & Heger 2007).
We therefore check whether the same problem holds for SN 2004et,
which differs in terms of both ejecta mass and explosion energy from
SN 2005cs. We adopt the pre-SN model with an envelope mass of
and a density distribution that closely resembles that of the evolutionary model (Utrobin & Chugai 2008). The hydrogen and helium are assumed to be mixed along the mass coordinate in a similar way to the optimal model (Fig. 2).
An optimal fit to the bolometric light curve and the evolution in
photospheric velocity is attained for an explosion energy of 1.3
1051 erg and a pre-SN radius of
.
Apparent disadvantages of the obtained model are an extremely narrow
initial peak of luminosity and a two step-like transition from the
plateau to the radioactive tail (Fig. 6a).
The latter behavior is similar to that demonstrated by the light curves
computed for the evolutionary pre-SN by Woosley & Heger (2007).
The narrow initial peak is related to the relatively small pre-SN
radius. However, one cannot increase the pre-SN radius to obtain a
superior fit because the photospheric velocity would then become
unacceptably low. A larger initial radius would produce a higher
luminosity, which, in turn, should be compensated by a decrease in the
explosion energy, consequently, leading to lower expansion velocities.
Even in the demonstrated model, the maximal velocity is only
9500 km s-1 (Fig. 6b), significantly lower than the observed maximal velocity of
12 000-13 000 km s-1.
We also computed the same model but without mixing between the helium
core and the hydrogen-rich envelope. This model provides an even poorer
fit because the ``bump'' at the end of the plateau becomes more boxy,
in sharp contrast to the observational light curve.
To summarize, the model including an explosion of the evolutionary pre-SN does not allow us to achieve a close fit to the bolometric light curve and the maximal expansion velocities of SN 2004et. This problem is not related to the evolutionary pre-SN itself. The one-dimensional hydrodynamics cannot reproduce the outcome of a real explosion in the evolutionary model, because multi-dimensional effects, in particular mixing between the helium core and the hydrogen envelope, play a crucial role during the explosion and shock propagation phases. The two-dimensional hydrodynamic model predicts that the Rayleigh-Taylor mixing at the helium/hydrogen interface reduces the high composition and density gradients (Müller et al. 1991). Our non-evolutionary pre-SN qualitatively takes this multi-dimensional effect into account, which ensures that the non-evolutionary model describes the light curve shape more successfully. A non-evolutionary pre-SN is also preferred by Baklanov et al. (2005) in their modeling of SN 1999em.
![]() |
Figure 6: Hydrodynamic model of SN 2004et for the evolutionary pre-SN. Panel a): the model bolometric light curve (solid line) overplotted on the observational data (see Fig. 4 legend for details). Panel b): the model photospheric velocity (solid line) and the observational photospheric velocities (see Fig. 5d legend for details). |
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2.4 Progenitor mass
The ejecta mass
combined with the collapsing core of
yields the pre-SN mass of 24.5
.
A progenitor mass on the main sequence is higher by the amount of
matter lost via the wind at the main-sequence and RSG phases.
For the main-sequence stage, we rely on the computations of Meynet
& Maeder (2003) for non-rotating stars with the mass-loss rate of Vink et al. (2001). They found that a star with an initial mass
lost
during the main sequence (Meynet & Maeder 2003). For the RSG stage, Meynet & Maeder (2003) used the mass-loss rate of de Jager (1988) and predicted that
and
main-sequence stars lost
and
,
respectively. With these estimates of the lost mass, we come to the progenitor mass of SN 2004et in the range of
.
A less massive progenitor is expected if we use the wind density
recovered for the SN 2004et pre-SN from X-ray observations. These
data suggest the mass-loss rate of (2-2.5)
yr-1, assuming the wind velocity of 10 km s-1 (Rho et al. 2007; Misra et al. 2007). Using the RSG life-time of 7
105 yr for the
main-sequence star (Hirshi et al. 2004), we find the mass lost at the RSG phase to be
with an uncertainty of
.
With the mass of
lost at the main-sequence phase (Hirshi et al. 2004), the total lost mass is then 2.4
.
The pre-SN mass of
combined with the lost mass results in the progenitor mass of 27
,
where the error includes the uncertainties in the ejecta mass and the
mass-loss rate. The progenitor mass of SN 2004et turns out to be
close to the maximal initial mass for SNe IIP according to the
present-day paradigm (Heger et al. 2003).
Table 1: Hydrodynamic models of type IIP supernovae.
Table 1 presents the
parameters of all the SNe IIP studied hydrodynamically. The listed
parameters are the pre-SN radius, the ejecta mass, the explosion
energy, the total 56Ni mass, the maximal velocity of 56Ni
mixing zone, and the minimal velocity of the hydrogen-rich envelope.
The ejecta and progenitor masses of SN 2004et are found to be
maximal among the well-studied SNe IIP. With the exception of the
initial radius for SN 1987A, the explosion energy and the total 56Ni mass show the most extreme variations (of one order of magnitude).
All SNe IIP are characterized by a deep mixing of hydrogen, indicated by the low value of
,
which is consistent with two-dimensional simulations (Müller et al. 1991; Kifonidis et al. 2003, 2006). The position of SN 2004et on the plots of explosion energy versus progenitor mass (Fig. 7a) and the total 56Ni mass versus the progenitor mass (Fig. 7b) strengthens the correlations recovered earlier for the SNe IIP studied hydrodynamically (Utrobin & Chugai 2008). We note that these correlations also infer the correlation between the explosion energy and the total 56Ni mass, which was found and discussed earlier by Nadyozhin (2003).
![]() |
Figure 7: Explosion energy a) and 56Ni mass b) versus hydrodynamic progenitor mass for five core-collapse SNe. |
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3 Discussion
3.1 Whether the hydrodynamic mass is overestimated?
The pre-SN mass recovered from the hydrodynamic modeling is very much
close to the progenitor mass.
It is, therefore, reasonable to refer to the progenitor mass thus
determined as the ``hydrodynamic'' mass. Surprisingly, the hydrodynamic
mass of the SN 2004et progenitor, 27
,
noticeably exceeds, by a factor of
,
the value of
recovered from the analysis of pre-explosion images (Smartt et al. 2009). A similarly large mass disparity has been found for SN 2005cs:
(Utrobin & Chugai 2008) versus
(Maund et al. 2005; Li et al. 2006; Eldridge et al. 2007).
These two cases of huge discrepancies in progenitor mass clearly
illustrate the high level of uncertainty in the mass problem.
The other side of this problem is that all the known hydrodynamic masses of SNe IIP progenitors are in the range
(Fig. 7). This mass distribution conflicts with the paradigm that SNe IIP originate from the mass range of
(Heger et al. 2003). Assuming the Salpeter initial mass function for SNe IIP rate in the
mass range and neglecting selection effects, we expect that five SNe should be found in the
mass range with a probability of only 0.004.
A quite different conclusion was reached by Smartt et al. (2009). They conclude that SNe IIP progenitors detected or undetected in pre-explosion images have masses in the range of
.
This significant difference in the progenitor-mass distributions
obtained by two methods and the mass discrepancy for SN 2004et and
SN 2005cs again implies that the determination of the progenitor
mass remains a difficult problem. Although the low masses of
SNe IIP progenitors from archival images also pose a problem for
the fate of massive RSG stars in the range of
(Smartt et al. 2009),
we address here only the possibility that hydrodynamic masses are
strongly overestimated compared to the real progenitor masses.
3.2 Could explosion asymmetry be a crucial missing factor?
To address the disagreements between progenitor mass determinations, we should consider possible problems with our numerical modeling. Among the missing factors that might affect the accuracy of the inferred SN parameters, the most apparent are: multi-group radiation transfer, full non-LTE treatment of gas excitation, time-dependent ionization, high spacial resolution of the shock front, multi-dimensional effects of the explosion and shock propagation, consideration of density perturbations related to vigorous convection in the RSG envelope. The effects produced by these factors perhaps differ in magnitude and some of the factors could be insignificant. However, detailed numerical studies based on advanced hydrodynamic models are needed to estimate the role of each factor. At present, we can only state firmly that the multi-group treatment of radiation transfer cannot notably change the inferred SN parameters. This conclusion is based on the comparison between the multi-group (Baklanov et al. 2005) and one-group (Utrobin 2007) approaches to the SN 1999em modeling.
A major drawback of our model may be its one-dimensional approximation. The multi-dimensional effects related to the Rayleigh-Taylor mixing between the helium core and the hydrogen envelope during the shock propagation smear the composition and density jumps (Müller et al. 1991). These effects are included artificially into our pre-SN model. More careful treatment of these effects with multi-dimensional radiation hydrodynamics could modify the inferred SN parameters.
Another multi-dimensional effect, which could potentially be of
importance, is the explosion asphericity. A growing amount of
observational data favor a picture in which the explosion of
SNe IIP is initiated by bipolar jets. SN 1987A provided us
with the first evidence of explosion asymmetry inferred from
polarization (cf. Jeffery 1991), line asymmetry (Haas et al. 1990), and direct imaging (Wang et al. 2002). During the last decade polarization has been detected in another five SNe IIP (Leonard & Filippenko 2001; Leonard et al. 2001, 2006). Two of these SNe IIP, SN 1999em and SN 2004dj, exhibit pronounced asymmetry in their H emission at the nebular stage, which is interpreted to be caused by asymmetric jets of 56Ni (Chugai 2007).
The absence of a pronounced polarization at the early photospheric
epoch indicates that the explosion asymmetry does not lead to the
asphericity of the hydrogen envelope (Leonard et al. 2001, 2006). The spherization would develop more successfully, if bipolar jets are thermal energy dominated (Couch et al. 2009).
However, the spherization of jets in the hydrogen envelope does not
preclude that the asymmetric explosion could result in the modification
of the velocity-mass distribution compared to the spherical explosion.
The disagreement between the mass measurements may then be resolved, if
the asymmetric explosion reproduces the observed light curve and
expansion velocities for the essentially lower ejecta mass compared to
the one-dimensional explosion model. To verify this possibility,
we would require multi-dimensional hydrodynamic modeling.
Using the spectra obtained by Sahu et al. (2006), we checked whether SN 2004et exhibited signatures of the explosion asymmetry. We found that nebular Hand
[O I] 6300, 6364 Å lines indeed exhibit asymmetry.
To quantify asymmetry effects, each line of the oxygen doublet on
day 301 was decomposed into three Gaussian components: symmetric,
red, and blue. The intensities of the corresponding components in blue
and red lines of the doublet were free parameters. Because the line
optical depth affects the doublet ratio, as in SN 1987A (Chugai 1988),
the line ratio permits us to recover the Sobolev optical depth and,
therefore, the oxygen number density. The effect is weakly dependent on
the electron temperature, which is assumed to be 5000 K.
![]() |
Figure 8: Oxygen doublet [O I] 6300, 6364 Å observed on day 301 (thin solid line). Zero radial velocity corresponds to the rest wavelength of 6300 Å. Thick solid line is the model doublet profile with all three Gaussian components, dashed line is the profile without the blue component, and dotted line is the symmetric component. |
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Table 2: Components of oxygen line decomposition.
The result of the doublet synthesis is shown in Fig. 8 with the model parameters listed in Table 2. The table columns give the radial velocity shift of the Gaussian component (v), its Doppler width (u), the amplitudes of its blue (A1) and red (A2) doublet components, and the number density of the line-emitting oxygen determined from the doublet ratio of each Gaussian component. We emphasize that the decomposition is not unique unless we constrain ourselves by the shape and number of components. The adopted decomposition procedure leads to a minimal contribution of the asymmetric components. Although the red and blue components are weaker than the symmetric one, the asymmetry is rather pronounced. Both asymmetric components have comparable integrated fluxes, but are not identical in terms of the Doppler widths and velocity shifts. These results infer a bipolar structure and a deviation from the point symmetry of the line-emitting gas in the inner layers of the SN envelope. We note our conclusion refers to the line-emitting gas, which is not identical to the overall oxygen distribution. It may well be that the asymmetry of the line-emitting oxygen is related primarily to the asymmetry of 56Ni ejecta (Chugai 2007). Interestingly, a combination of the bipolar structure and the deviation from the point symmetry is a specific feature of SN 1987A, SN 1999em, and SN 2004dj (Chugai 2007). The case of SN 2004et thus provides further support to the conjecture that the explosion asymmetry is an ubiquitous phenomenon of SNe IIP.
Remarkably, the oxygen number density for the symmetric and blue components (Table 2) is comparable, to within a factor of unity, with the oxygen density of
(0.5-1.4)
109 cm-3 for the optimal model in the velocity range v < 2500 km s-1.
In the latter case, we assume that the oxygen density is equal to the
total matter density. This coincidence suggests that whatever the role
of asymmetry, the related effects do not strongly modify the density
distribution of our optimal model in the inner layers with velocities v < 2000 km s-1.
Of course, this does not preclude that the velocity-density
distribution in outer layers could be modified significantly as a
result of the aspherical explosion.
4 Conclusions
Our goal was to recover the parameters of the hydrodynamic model of the luminous type IIP SN 2004et.
We obtained the optimal parameter set: the ejecta mass
,
the explosion energy
1051 erg, the pre-SN radius R0=1500
,
and the 56Ni mass
.
The inferred ejecta mass and explosion energy are maximal among all the
known SNe IIP explored by means of radiation hydrodynamics. The
parameters of SN 2004et strengthen correlations between the
explosion energy and progenitor mass, and between the total 56Ni mass and progenitor mass discussed earlier (Utrobin & Chugai 2008).
The progenitor mass of SN 2004et, estimated by combining the pre-SN mass and the mass lost via the stellar wind, turns out to be significantly, by a factor of 2-3, higher than the main-sequence mass recovered from the pre-explosion images. This and the disagreement between mass estimates found earlier for SN 2005cs raise serious concern about the reliability of the progenitor mass recovered from the hydrodynamic modeling. We speculate that among the pitfalls of our hydrodynamic code, the most crucial could be the one-dimensional approximation. The artificial mixing between the helium core and the hydrogen envelope, which we use to simulate real mixing, could be flawed, while explosion asphericity is completely ignored. The evidence of the explosion asphericity of SN 2004et is inferred from the nebular lines, which thus supports the view that the explosion asymmetry is an ubiquitous phenomenon for SNe IIP.
AcknowledgementsWe are indebted to D. K. Sahu for sending us spectra of SN 2004et. One of us (VU) is grateful to Wolfgang Hillebrandt for the possibility to work at the MPA. We thank the anonymous referee for useful comments on our manuscript.
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All Tables
Table 1: Hydrodynamic models of type IIP supernovae.
Table 2: Components of oxygen line decomposition.
All Figures
![]() |
Figure 1:
Density distribution as a function of interior mass a) and
radius b) for the optimal pre-SN model. The central core of 1.6 |
Open with DEXTER | |
In the text |
![]() |
Figure 2: The mass fraction of hydrogen (solid line), helium (long dashed line), CNO elements (short dashed line), and Fe-peak elements including radioactive 56Ni (dotted line) in the ejecta of the optimal model. |
Open with DEXTER | |
In the text |
![]() |
Figure 3:
The density and the 56Ni mass fraction as a function of velocity for the optimal model at t=50 days. Dash-dotted line is the density distribution fit
|
Open with DEXTER | |
In the text |
![]() |
Figure 4:
The calculated bolometric light curve of the optimal model (solid line) overplotted on the bolometric data of SN 2004et evaluated from the |
Open with DEXTER | |
In the text |
![]() |
Figure 5: Optimal hydrodynamic model. Panels a)-c): the calculated B, V, and R light curves (solid lines) compared with the corresponding observations of SN 2004et obtained by Sahu et al. (2006) (open circles). Panel d): the calculated photospheric velocity (solid line) is compared with photospheric velocities estimated from the absorption minimum of the Fe II 5169 Å line (open circles) by Sahu et al. (2006) and recovered from the Na I doublet profile (filled circles). |
Open with DEXTER | |
In the text |
![]() |
Figure 6: Hydrodynamic model of SN 2004et for the evolutionary pre-SN. Panel a): the model bolometric light curve (solid line) overplotted on the observational data (see Fig. 4 legend for details). Panel b): the model photospheric velocity (solid line) and the observational photospheric velocities (see Fig. 5d legend for details). |
Open with DEXTER | |
In the text |
![]() |
Figure 7: Explosion energy a) and 56Ni mass b) versus hydrodynamic progenitor mass for five core-collapse SNe. |
Open with DEXTER | |
In the text |
![]() |
Figure 8: Oxygen doublet [O I] 6300, 6364 Å observed on day 301 (thin solid line). Zero radial velocity corresponds to the rest wavelength of 6300 Å. Thick solid line is the model doublet profile with all three Gaussian components, dashed line is the profile without the blue component, and dotted line is the symmetric component. |
Open with DEXTER | |
In the text |
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