arXiv subjects

Nozomu Tominaga

Publications and source records attributed to Nozomu Tominaga.

At least 145 records · Page 8Linked to original sources

arXiv2010

Fallback Supernovae: A Possible Origin of Peculiar Supernovae with Extremely Low Explosion Energies

We perform hydrodynamical calculations of core-collapse supernovae (SNe) with low explosion energies. These SNe do not have enough energy to eject the whole progenitor and most of the progenitor falls back to the central remnant. We show that such fallback SNe can have a variety of light curves (LCs) but their photospheric velocities can only have some limited values with lower limits. We also perform calculations of nucleosynthesis and LCs of several fallback SN model, and find that a fallback SN from the progenitor with a main-sequence mass of 13 Msun can account for the properties of the peculiar Type Ia supernova SN 2008ha. The kinetic energy and ejecta mass of the model are 1.2*10^{48} erg and 0.074 Msun, respectively, and the ejected 56Ni mass is 0.003 Msun. Thus, SN 2008ha can be a core-collapse SN with a large amount of fallback. We also suggest that SN 2008ha could have been accompanied with long gamma-ray bursts and long gamma-ray bursts without associated SNe may be accompanied with very faint SNe with significant amount of fallback which are similar to SN 2008ha.

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arXiv2010

A Core-Collapse Supernova Model for the Extremely Luminous Type Ic Supernova 2007bi: An Alternative to the Pair-Instability Supernova Model

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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arXiv2010

Formation and Evolution of Dust in Type IIb Supernova with Application to the Cassiopeia A Supernova Remnant

We investigate the formation of dust grains in the ejecta of a SN IIb and their evolution in the shocked gas in the SNR by considering the uniform and power-law density structures for the CSM. Based on these calculations, we also simulate the time evolution of thermal emission from the shock-heated dust in the SNR and compare the results with the observations of Cas A SNR. We find that the total mass of dust formed in the SN IIb is as large as 0.167 M_sun but the average radius of dust is smaller than 0.01 mum and is significantly different from those in SNe II-P with the massive H-envelope. In the explosion with the small-mass H-envelope, the expanding He core undergoes little deceleration, so that the gas density in the He core is too low for large-sized grains to form. In addition, the low-mass H-envelope of the SN IIb leads to the early arrival of the reverse shock at the dust-forming region. If the CSM is more or less spherical, therefore, the newly formed grains would be completely destroyed in the relatively dense shocked gas for the CSM density of n_H > 0.1 cm^{-3}. However, the actual CSM is likely to be non-spherical, so that a part of grains could be ejected into the ISM without being shocked. We demonstrate that the time evolution of the SED by thermal dust emission is sensitive to the ambient gas density and structure that affects the passage of the reverse shock into the ejecta. Thus, the SED evolution well reflects the evolution of dust through erosion by sputtering and stochastic heating. For Cas A, we consider the CSM produced by the steady mass loss of ~8x10^{-5} M_sun/yr during the supergiant phase. Then we find the infrared SED of Cas A is reasonably reproduced by thermal emission from the newly formed dust of 0.08 M_sun, which consists of 0.008 M_sun shocked warm dust and 0.072 M_sun unshocked cold dust.

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arXiv2009

Spectropolarimetry of the Unique Type Ib Supernova 2005bf: Larger Asymmetry Revealed by Later-Phase Data

We present an optical spectropolarimetric observation of the unique Type Ib supernova (SN) 2005bf at 8 days after the second maximum. The data, combined with the polarization spectrum taken at 6 days before the second maximum (Maund et al. 2007a), enable us to closely examine the intrinsic properties of the SN. The polarization percentage is smaller at the later epoch over a wide wavelength range, while the position angle is similar at the two epochs. We find that an assumption of complete depolarization of strong lines at the emission peak is not necessarily correct. The intrinsic polarization of the SN is larger, and thus, the ejecta of SN 2005bf would be more asymmetric than previously expected. The axis ratio of the photosphere projected on the sky deviates from unity by at least 20 %. If the position angle of interstellar polarization is aligned with the spiral arm of the host galaxy, the deviation is larger than 25 %. The line polarization at the He I, Ca II and Fe II lines is also smaller at the later epoch. The changes in the position angle across these lines, which were observed at the earlier epoch, are still marginally present at the later epoch. The similar polarimetric behavior suggests that the distributions of these ions are correlated. Properties of polarization, as well as the light curve and the spectra both at photospheric and nebular phases, can be explained by an aspherical, possibly unipolar explosion of a WN star in which the blob of 56Ni penetrates C+O core and stops within the He layer.

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arXiv2009

Nebular Phase Observations of the Type Ib Supernova 2008D/X-ray Transient 080109: Side-Viewed Bipolar Explosion

We present optical spectroscopic and photometric observations of supernova (SN) 2008D, associated with the luminous X-ray transient 080109, at >300 days after the explosion (nebular phases). We also give flux measurements of emission lines from the H II region at the site of the SN, and estimates of the local metallicity. The brightness of the SN at nebular phases is consistent with the prediction of the explosion models with an ejected 56Ni mass of 0.07 Msun, which explains the light curve at early phases. The [O I] line in the nebular spectrum shows a double-peaked profile while the [Ca II] line does not. The double-peaked [O I] profile strongly indicates that SN 2008D is an aspherical explosion. The profile can be explained by a torus-like distribution of oxygen viewed from near the plane of the torus. We suggest that SN 2008D is a side-viewed, bipolar explosion with a viewing angle of > 50^{\circ} from the polar direction.

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arXiv2009

First Stars -- Type Ib Supernovae Connection

The very peculiar abundance patterns observed in extremely metal-poor (EMP) stars can not be explained by ordinary supernova nucleosynthesis but can be well-reproduced by nucleosynthesis in hyper-energetic and hyper-aspherical explosions, i.e., Hypernovae (HNe). Previously, such HNe have been observed only as Type Ic supernovae. Here, we examine the properties of recent Type Ib supernovae (SNe Ib). In particular, SN Ib 2008D associated with the luminous X-ray transient 080109 is found to be a more energetic explosion than normal core-collapse supernovae. We estimate that the progenitor's main sequence mass is 20--25 M_sun and a kinetic energy of explosion is ~ 6 x 10^{51} erg. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. Such energetic SNe Ib can make important contribution to the chemical enrichment in the early Universe.

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arXiv2009

Chemical Yields from Supernovae and Hypernovae

We review the final stages of stellar evolution, supernova properties, and chemical yields as a function of the progenitor's mass M. (1) 8 - 10 Ms stars are super-AGB stars when the O+Ne+Mg core collapses due to electron capture. These AGB-supernovae may constitute an SN 2008S-like sub-class of Type IIn supernovae. These stars produce little alpha-elements and Fe-peak elements, but are important sources of Zn and light p-nuclei. (2) 10 - 90 Ms stars undergo Fe-core collapse. Nucleosynthesis in aspherical explosions is important, as it can well reproduce the abundance patterns observed in extremely metal-poor stars. (3) 90 - 140 Ms stars undergo pulsational nuclear instabilities at various nuclear burning stages, including O and Si-burning. (4) 140 - 300 Ms stars become pair-instability supernovae, if the mass loss is small enough. (5) Stars more massive than 300 Ms undergo core-collapse to form intermediate mass black holes.

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arXiv2009

Dust in Supernovae; Formation and Evolution

Core--collapsed supernovae (CCSNe) have been considered to be one of sources of dust in the universe. What kind and how much mass of dust are formed in the ejecta and are injected into the interstellar medium (ISM) depend on the type of CCSNe, through the difference in the thickness (mass) of outer envelope. In this review, after summarizing the existing results of observations on dust formation in CCSNe, we investigate formation of dust in the ejecta and its evolution in the supernova remnants (SNRs) of Type II--P and Type IIb SNe. Then, the time evolution of thermal emission from dust in the SNR of Type IIb SN is demonstrated and compared with the observation of Cas A. We find that the total dust mass formed in the ejecta does not so much depend on the type; $\sim 0.3-0.7 M_{\odot}$ in Type II--P SNe and $\sim 0.13 M_{\odot}$ in Type IIb SN. However the size of dust sensitively depends on the type, being affected by the difference in the gas density in the ejecta: the dust mass is dominated by grains with radii larger than 0.03 $μ$m in Type II-P, and less than 0.006 $μ$m in Type IIb, which decides the fate of dust in the SNR. The surviving dust mass is $\sim 0.04-0.2 M_{\odot}$ in the SNRs of Type II--P SNe for the ambient hydrogen density of $n_{\rm H}=10.0-1.0$ cm$^{-3}$, while almost all dust grains are destroyed in the SNR of Type IIb. The spectral energy distribution (SED) of thermal emission from dust in SNR well reflects the evolution of dust grains in SNR through erosion by sputtering and stochastic heating. The observed SED of Cas A SNR is reasonably reproduced by the model of dust formation and evolution for Type IIb SN.

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arXiv2009

Type Ib Supernova 2008D associated with the Luminous X-ray Transient 080109: An Energetic Explosion of a Massive Helium Star

We present a theoretical model for supernova (SN) 2008D associated with the luminous X-ray transient 080109. The bolometric light curve and optical spectra of the SN are modelled based on the progenitor models and the explosion models obtained from hydrodynamic/nucleosynthetic calculations. We find that SN 2008D is a more energetic explosion than normal core-collapse supernovae, with an ejecta mass of Mej = 5.3 +- 1.0 Msun and a kinetic energy of E = 6.0 +- 2.5 x 10^{51} erg. The progenitor star of the SN has a 6-8 Msun He core with essentially no H envelope (< 5 x 10^{-4} Msun) prior to the explosion. The main-sequence mass of the progenitor is estimated to be Mms =20-25 Msun, with additional systematic uncertainties due to convection, mass loss, rotation, and binary effects. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. The mass of the central remnant is estimated as 1.6 - 1.8 Msun, which is near the boundary between neutron star and black hole formation.

astro-ph↗

arXiv2009

The Extremely Luminous Supernova 2006gy at Late Phase: Detection of Optical Emission from Supernova

We performed optical spectroscopy and photometry of SN 2006gy at late time, ~400 days after the explosion, with the Subaru/FOCAS in a good seeing condition. We found that the SN faded by ~3 mag from ~200 to ~400 days after the explosion (i.e., by ~5 mag from peak to ~400 days) in R band. The overall light curve is marginally consistent with the 56Ni heating model, although the flattening around 200 days suggests the optical flux declined more steeply between ~200 and ~400 days. The late time spectrum was quite peculiar among all types of SNe. It showed many intermediate width (~2000 km/s FWHM) emission lines, e.g., [Fe II], [Ca II], and Ca II. The absence of the broad [O I] 6300, 6364 line and weakness of [Fe II] and [Ca II] lines compared with Ca II IR triplet would be explained by a moderately high electron density in the line emitting region. This high density assumption seems to be consistent with the large amount of ejecta and low expansion velocity of SN 2006gy. The H-alpha line luminosity was as small as ~1x10^39 erg/s, being comparable with those of normal Type II SNe at similar epochs. Our observation indicates that the strong CSM interaction had almost finished by ~400 days. If the late time optical flux is purely powered by radioactive decay, at least M_Ni ~ 3 M_sun should be produced at the SN explosion. In the late phase spectrum, there were several unusual emission lines at 7400--8800 AA and some of them might be due to Ti or Ni synthesized at the explosion. (abridged)

astro-ph.SR↗

arXiv2009

Nucleosynthesis of 56Ni in wind-driven Supernova Explosions and Constraints on the Central Engine of Gamma-Ray Bursts

Theoretically expected natures of a supernova driven by a wind/jet are discussed. Approximate analytical formulations are derived to clarify basic physical processes involved in the wind/jet-driven explosions, and it is shown that the explosion properties are characterized by the energy injection rate (Edot_iso) and the mass injection rate (Mdot_iso). To explain observations of SN 1998bw associated with Gamma-Ray Burst (GRB) 980425, the following conditions are required: Edot_iso Mdot_iso > ~ 10^{51} erg M_sun s^{-2} and Edot_iso > ~ 2 x 10^{52} erg s^{-1} (if the wind Lorentz factor Gamma_w ~ 1) or Edot_iso > ~ 7 x 10^{52} erg s^{-1} (if Gamma_w >> 1). In SN 1998bw, 56Ni (~ 0.4M_sun) is probably produced in the shocked stellar mantle, not in the wind. The expected natures of SNe, e.g., ejected 56Ni masses and ejecta masses, vary depending on Edot_iso and Mdot_iso. The sequence of the SN properties from high Edot_iso and Mdot_iso to low Edot_iso and Mdot_iso is the following: SN 1998bw-like -- intermediate case -- low mass ejecta (< ~ 1M_sun$) where 56Ni is from the wind -- whole collapse. This diversity may explain the diversity of supernovae associated with GRBs. Our result can be used to constrain natures of the wind/jet, which is linked to the central engine of GRBs, by studying properties of the associated supernovae.

astro-ph.HE↗

arXiv2008

Supernova Nucleosynthesis and Extremely Metal-Poor Stars

We investigate hydrodynamical and nucleosynthetic properties of the jet-induced explosion of a population III $40M_\odot$ star and compare the abundance patterns of the yields with those of the metal-poor stars. We conclude that (1) the ejection of Fe-peak products and the fallback of unprocessed materials can account for the abundance patterns of the extremely metal-poor (EMP) stars and that (2) the jet-induced explosion with different energy deposition rates can explain the diversity of the abundance patterns of the metal-poor stars. Furthermore, the abundance distribution after the explosion and the angular dependence of the yield are shown for the models with high and low energy deposition rates $\dot{E}_{\rm dep}=120\times10^{51} {\rm ergs s^{-1}}$ and $1.5\times10^{51} {\rm ergs s^{-1}}$. We also find that the peculiar abundance pattern of a Si-deficient metal-poor star HE 1424--0241 can be reproduced by the angle-delimited yield for $θ=30^\circ-35^\circ$ of the model with $\dot{E}_{\rm dep}=120\times10^{51} {\rm ergs s^{-1}}$.

astro-ph↗

arXiv2008

Evolution of newly formed dust in Population III supernova remnants and its impact on the elemental composition of Population II.5 stars

We investigate the evolution of dust formed in Population III supernovae (SNe) by considering its transport and processing by sputtering within the SN remnants (SNRs). We find that the fates of dust grains within SNRs heavily depend on their initial radii $a_{\rm ini}$. For Type II SNRs expanding into the ambient medium with density of $n_{\rm H,0} = 1$ cm$^{-3}$, grains of $a_{\rm ini} < 0.05$ $μ$m are detained in the shocked hot gas and are completely destroyed, while grains of $a_{\rm ini} > 0.2$ $μ$m are injected into the surrounding medium without being destroyed significantly. Grains with $a_{\rm ini}$ = 0.05-0.2 $μ$m are finally trapped in the dense shell behind the forward shock. We show that the grains piled up in the dense shell enrich the gas up to 10$^{-6}-10^{-4}$ $Z_\odot$, high enough to form low-mass stars with 0.1-1 $M_\odot$. In addition, [Fe/H] in the dense shell ranges from -6 to -4.5, which is in good agreement with the ultra-metal-poor stars with [Fe/H] < -4. We suggest that newly formed dust in a Population III SN can have great impacts on the stellar mass and elemental composition of Population II.5 stars formed in the shell of the SNR.

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arXiv2008

Supernova Nucleosynthesis in the Early Universe

The first metal enrichment in the universe was made by supernova (SN) explosions of population (Pop) III stars. The trace remains in abundance patterns of extremely metal-poor (EMP) stars. We investigate the properties of nucleosynthesis in Pop III SNe by means of comparing their yields with the abundance patterns of the EMP stars. We focus on (1) jet-induced SNe with various energy deposition rates [$\dot{E}_{\rm dep}=(0.3-1500)\times10^{51}{\rm ergs s^{-1}}$], and (2) SNe of stars with various main-sequence masses ($M_{\rm ms}=13-50M_\odot$) and explosion energies [$E=(1-40)\times10^{51}$ergs]. The varieties of Pop III SNe can explain varieties of the EMP stars: (1) higher [C/Fe] for lower [Fe/H] and (2) trends of abundance ratios [X/Fe] against [Fe/H].

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arXiv2008

Aspherical Properties of Hydrodynamics and Nucleosynthesis in Jet-induced Supernovae

Jet-induced supernovae (SNe) have been suggested to occur in gamma-ray bursts (GRBs) and highly-energetic SNe (hypernovae). I investigate hydrodynamical and nucleosynthetic properties of the jet-induced explosion of a population III $40_\odot$ star with a two-dimensional special relativistic hydrodynamical code. The abundance distribution after the explosion and the angular dependence of the yield are obtained for the models with high and low energy deposition rates $\dot{E}_{\rm dep}=120\times10^{51} {\rm ergs s^{-1}}$ and $1.5\times10^{51} {\rm ergs s^{-1}}$. The ejection of Fe-peak products and the fallback of unprocessed materials in the jet-induced SNe account for the abundance patterns of the extremely metal-poor (EMP) stars. It is also found that the peculiar abundance pattern of a Si-deficient metal-poor star HE 1424--0241 is reproduced by the angle-delimited yield for $θ=30^\circ-35^\circ$ of the model with $\dot{E}_{\rm dep}=120\times10^{51} {\rm ergs s^{-1}}$. Furthermore, I compare the yield of the jet-induced explosion with that of the spherical explosion and confirm the ejection and fallback in the jet-induced explosion is almost equivalent to the "mixing-fallback" in spherical explosions. In contrast to the spherical models, however, the high-entropy environment is realized in the jet-induced explosion and thus [(Sc, Ti, V, Cr, Co, Zn)/Fe] are enhanced. The enhancements of [Sc/Fe] and [Ti/Fe] improve agreements with the abundance patterns of the EMP stars.

astro-ph↗

arXiv2008

The metamorphosis of Supernova SN2008D/XRF080109: a link between Supernovae and GRBs/Hypernovae

The only supernovae (SNe) to have shown early gamma-ray or X-ray emission thus far are overenergetic, broad-lined Type Ic SNe (Hypernovae - HNe). Recently, SN 2008D shows several novel features: (i) weak XRF, (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SNIc HNe, (iv) development of He lines as in SNeIb. Detailed analysis shows that SN 2008D was not a normal SN: its explosion energy (KE ~ 6*10^{51} erg) and ejected mass (~7 Msun) are intermediate between normal SNeIbc and HNe. We derive that SN 2008D was originally a ~30Msun star. When it collapsed a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes.

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arXiv2008

The evolution of the peculiar Type Ia supernova SN 2005hk over 400 days

$UBVRI$ photometry and medium resolution optical spectroscopy of peculiar Type Ia supernova SN 2005hk are presented and analysed, covering the pre-maximum phase to around 400 days after explosion. The supernova is found to be underluminous compared to "normal" Type Ia supernovae. The photometric and spectroscopic evolution of SN 2005hk is remarkably similar to the peculiar Type Ia event SN 2002cx. The expansion velocity of the supernova ejecta is found to be lower than normal Type Ia events. The spectra obtained $\gsim 200$ days since explosion do not show the presence of forbidden [\ion{Fe}{ii}], [\ion{Fe}{iii}] and [\ion{Co}{iii}] lines, but are dominated by narrow, permitted \ion{Fe}{ii}, NIR \ion{Ca}{ii} and \ion{Na}{i} lines with P-Cygni profiles. Thermonuclear explosion model with Chandrasekhar mass ejecta and a kinetic energy smaller ($\KE = 0.3 \times 10^{51} {\rm ergs}$) than that of canonical Type Ia supernovae is found to well explain the observed bolometric light curve. The mass of \Nifs synthesized in this explosion is $0.18 \Msun$. The early spectra are successfully modeled with this less energetic model with some modifications of the abundance distribution. The late spectrum is explained as a combination of a photospheric component and a nebular component.

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arXiv2008

Chemical Abundances of the Secondary Star in the Black Hole X-ray Binary XTE J1118+480

Following the recent abundance measurements of Mg, Al, Ca, Fe, and Ni in the black hole X-ray binary XTE J1118+480 using medium-resolution Keck II/ESI spectra of the secondary star (González Hernández et al. 2006), we perform a detailed abundance analysis including the abundances of Si and Ti. These element abundances, higher than solar, indicate that the black hole in this system formed in a supernova event, whose nucleosynthetic products could pollute the atmosphere of the secondary star, providing clues on the possible formation region of the system, either Galactic halo, thick disk, or thin disk. We explore a grid of explosion models with different He core masses, metallicities, and geometries. Metal-poor models associated with a formation scenario in the Galactic halo provide unacceptable fits to the observed abundances, allowing us to reject a halo origin for this X-ray binary. The thick-disk scenario produces better fits, although they require substantial fallback and very efficient mixing processes between the inner layers of the explosion and the ejecta, making quite unlikely an origin in the thick disk. The best agreement between the model predictions and the observed abundances is obtained for metal-rich progenitor models. In particular, non-spherically symmetric models are able to explain, without strong assumptions of extensive fallback and mixing, the observed abundances. Moreover, asymmetric mass ejection in a supernova explosion could account for the required impulse necessary to launch the system from its formation region in the Galactic thin disk to its current halo orbit.

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