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تسجيل مستخدم جديدA Core-Collapse Supernova Model for the Extremely Luminous Type Ic Supernova 2007bi: An Alternative to the Pair-Instability Supernova Model
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We present a core-collapse supernova model for the extremely luminous Type Ic supernova 2007bi. By performing numerical calculations of hydrodynamics, nucleosynthesis, and radiation transport, we find that SN 2007bi is consistent with the core-collapse supernova explosion of a 43 Msun carbon and oxygen core obtained from the evolution of a progenitor star with a main sequence mass of 100 Msun and metallicity of Z = Zsun/200, from which its hydrogen and helium envelopes are artificially stripped. The ejecta mass and the ejecta kinetic energy of the models are 40 Msun and 3.6*10^{52} erg. The ejected 56Ni mass is as large as 6.1 Msun, which results from the explosive nucleosynthesis with large explosion energy. We also confirm that SN 2007bi is consistent with a pair-instability supernova model as has recently been claimed. We show that the earlier light curve data can discriminate between the models for such luminous supernovae.
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SN 2007bi is an extremely luminous Type Ic supernova. This supernova is thought to be evolved from a very massive star, and two possibilities have been proposed for the explosion mechanism. One possibility is a pair-instability supernova with an M_{C
O} ~ 100 M_sun CO core progenitor. Another possibility is a core-collapse supernova with M_{CO} ~ 40 M_sun. We investigate the evolution of very massive stars with main-sequence mass M_{MS} = 100 - 500 M_sun and Z_0 = 0.004, which is in the metallicity range of the host galaxy of SN 2007bi, to constrain the progenitor of SN 2007bi. The supernova type relating to the surface He abundance is also discussed. The main-sequence mass of the progenitor exploding as a pair-instability supernova could be M_{MS} ~ 515 - 575 M_sun. The minimum main-sequence mass could be 310 M_sun when uncertainties in the mass-loss rate are considered. A star with M_{MS} ~ 110 - 280 M_sun evolves to a CO star, appropriate for the core-collapse supernova of SN 2007bi. Arguments based on the probability of pair-instability and core-collapse supernovae favour the hypothesis that SN 2007bi originated from a core-collapse supernova event.
SN~2007D is a nearby (redshift $z = 0.023146$), luminous Type Ic supernova (SN) having a narrow light curve (LC) and high peak luminosity. Previous research based on the assumption that it was powered by the $^{56}$Ni cascade decay suggested that the
inferred $^{56}$Ni mass and the ejecta mass are $sim 1.5$M$_{odot}$ and $sim 3.5$M$_{odot}$, respectively. In this paper, we employ some multiband LC models to model the $R$-band LC and the color ($V-R$) evolution of SN~2007D to investigate the possible energy sources powering them. We find that the pure $^{56}$Ni model is disfavored; the multiband LCs of SN~2007D can be reproduced by a magnetar whose initial rotational period $P_{0}$ and magnetic field strength $B_p$ are $7.28_{-0.21}^{+0.21}$ (or $9.00_{-0.42}^{+0.32}$) ms and $3.10_{-0.35}^{+0.36}times 10^{14}$ (or $2.81_{-0.44}^{+0.43}times 10^{14}$) G, respectively. By comparing the spectrum of SN~2007D with that of some superluminous SNe (SLSNe), we find that it might be a luminous SN like several luminous ``gap-filler optical transients that bridge ordinary and SLSNe, rather than a genuine SLSN.
We investigate the possibility of a super-luminous Type Ic core-collapse supernovae producing a large amount of 56Ni. Very massive stars with a main-sequence mass larger than 100 Msun and a metallicity 0.001 < Z < 0.004 are expected to explode as sup
er-luminous Type Ic supernovae. Stars with ~ 110 - 150 Msun and Z < 0.001 would explode as Type Ic pulsational pair-instability supernovae if the whole H and He layers has been lost by the mass loss during pulsational pair-instability. We evaluate the total ejecta mass and the yields of 56Ni, O, and Si in core-collapse supernovae evolved from very massive stars. We adopt 43.1 and 61.1 Msun WO stars with Z=0.004 as supernova progenitors expected to explode as Type Ic core-collapse supernovae. These progenitors have masses of 110 and 250 Msun at the zero-age main sequence. Spherical explosions with an explosion energy larger than 2e52 erg produce more than 3.5 Msun 56Ni, enough to reproduce the light curve of SN 2007bi. Asphericity of the explosion affects the total ejecta mass as well as the yields of 56Ni, O, and Si. Aspherical explosions of the 110 and 250 Msun models reproduce the 56Ni yield of SN 2007bi. These explosions will also show large velocity dispersion. An aspherical core-collapse supernova evolved from a very massive star is a possibility of the explosion of SN 2007bi.
We investigate the action of the magnetorotational instability (MRI) in the context of iron-core collapse. Exponential growth of the field on the rotation time scale by the MRI will dominate the linear growth process of field line wrapping with the s
ame characteristic time. We examine a variety of initial rotation states, with solid body rotation or a gradient in rotational velocity, that correspond to models in the literature. A relatively modest value of the initial rotation, a period of ~ 10 s, will give a very rapidly rotating PNS and hence strong differential rotation with respect to the infalling matter. We assume conservation of angular momentum on spherical shells. Results are discussed for two examples of saturation fields, a fiducial field that corresponds to Alfven velocity = rotational velocity and a field that corresponds to the maximum growing mode of the MRI. Modest initial rotation velocities of the iron core result in sub-Keplerian rotation and a sub-equipartition magnetic field that nevertheless produce substantial MHD luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G develop within 300 msec after bounce with an associated MHD luminosity of about 10^{52} erg/s. Bi-polar flows driven by this MHD power can affect or even cause the explosions associated with core-collapse supernovae.
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