arXiv subjects

Nozomu Tominaga

Publications and source records attributed to Nozomu Tominaga.

At least 127 records · Page 7Linked to original sources

arXiv2015

Time-dependent Multi-group Multidimensional Relativistic Radiative Transfer Code Based On Spherical Harmonic Discrete Ordinate Method

We develop a time-dependent multi-group multidimensional relativistic radiative transfer code, which is required to numerically investigate radiation from relativistic fluids involved in, e.g., gamma-ray bursts and active galactic nuclei. The code is based on the spherical harmonic discrete ordinate method (SHDOM) that evaluates a source function including anisotropic scattering in spherical harmonics and implicitly solves the static radiative transfer equation with a ray tracing in discrete ordinates. We implement treatments of time dependence, multi-frequency bins, Lorentz transformation, and elastic Thomson and inelastic Compton scattering to the publicly available SHDOM code. Our code adopts a mixed frame approach; the source function is evaluated in the comoving frame whereas the radiative transfer equation is solved in the laboratory frame. This implementation is validated with various test problems and comparisons with results of a relativistic Monte Carlo code. These validations confirm that the code correctly calculates intensity and its evolution in the computational domain. The code enables us to obtain an Eddington tensor that relates first and third moments of intensity (energy density and radiation pressure) and is frequently used as a closure relation in radiation hydrodynamics calculations.

astro-ph.IM↗

arXiv2015

OISTER Optical and Near-Infrared Observations of Type Iax Supernova 2012Z

We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared wavelengths from immediately after the explosion until $\sim$ $260$ days after the maximum luminosity using the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) Target-of-Opportunity (ToO) program and the Subaru telescope. We found that the near-infrared (NIR) light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes ($M_{J}\sim-18.1$ mag and $M_{H}\sim-18.3$ mag) and the rate of decline of the light curve ($Δ$ $m_{15}$($B$)$=1.6 \pm 0.1$ mag) are very similar to those of SN 2005hk ($M_{J}\sim-17.7$ mag, $M_{H}\sim$$-18.0$ mag, and $Δ$ $m_{15}$($B$)$\sim1.6$ mag), yet differ significantly from SNe 2008ha and 2010ae ($M_{J}\sim-14 - -15$ mag and $Δ$ $m_{15}$($B$)$\sim2.4-2.7$ mag). The estimated rise time is $12.0 \pm 3.0$ days, which is significantly shorter than that of SN 2005hk or any other Ia SNe. The rapid rise indicates that the $^{56}$Ni distribution may extend into the outer layer or that the effective opacity may be lower than that in normal SNe Ia. The late-phase spectrum exhibits broader emission lines than those of SN 2005hk by a factor of 6--8. Such high velocities of the emission lines indicate that the density profile of the inner ejecta extends more than that of SN 2005hk. We argue that the most favored explosion scenario is a `failed deflagration' model, although the pulsational delayed detonations is not excluded.

astro-ph.SR↗

arXiv2015

How Much Can $^{56}$Ni Be Synthesized by Magnetar Model for Long Gamma-ray Bursts and Hypernovae?

A rapidly rotating neutron star with strong magnetic fields, called magnetar, is a possible candidate for the central engine of long gamma-ray bursts and hypernovae (HNe). We solve the evolution of a shock wave driven by the wind from magnetar and evaluate the temperature evolution, by which we estimate the amount of $^{56}$Ni that produces a bright emission of HNe. We obtain a constraint on the magnetar parameters, namely the poloidal magnetic field strength ($B_p$) and initial angular velocity ($Ω_i$), for synthesizing enough $^{56}$Ni mass to explain HNe ($M_{^{56}\mathrm{Ni}}\gtrsim 0.2M_\odot$), i.e. $(B_p/10^{16}~\mathrm{G})^{1/2}(Ω_i/10^4~\mathrm{rad~s}^{-1})\gtrsim 0.7$.

astro-ph.HE↗

arXiv2015

Nuclear Composition of Magnetized GRB Jets

We investigate the fraction of metal nuclei in the relativistic jets of gamma-ray bursts associated with core-collapse supernovae. We simulate the fallback in jet-induced explosions with two-dimensional relativistic hydrodynamics calculations and the jet acceleration with steady, radial, relativistic magnetohydrodynamics calculations, and derive detail nuclear composition of the jet by postprocessing calculation. We found that if the temperature at the jet launch site is above $4.7\times 10^9$K, quasi-statistical equilibrium (QSE) is established and heavy nuclei are dissociated to light particles such as $^4$He during the acceleration of the jets. The criterion for the survival of metal nuclei is written in terms of the isotropic jet luminosity as $L_{\rm j}^{\rm iso} \lesssim 3.9\times 10^{50}(R_{\rm i}/10^7{\rm cm})^2 (1+σ_{\rm i})~{\rm erg~s^{-1}}$, where $R_{\rm i}$ and $σ_{\rm i}$ are the initial radius of the jets and the initial magnetization parameter, respectively. If the jet is initially dominated by radiation field (i.e., $σ_{\rm i} \ll 1$) and the isotropic luminosity is relatively high ($L_{\rm j}^{\rm iso}\gtrsim 4\times 10^{52}~{\rm erg s^{-1}}$), the metal nuclei cannot survive in the jet. On the other hand, if the jet is mainly accelerated by magnetic field (i.e., $σ_{\rm i} \gg1$), metal nuclei initially contained in the jet can survive without serious dissociation even for the case of high luminosity jet. If the jet contains metal nuclei, the dominant nuclei are $^{28}$Si, $^{16}$O, and $^{32}$S and the mean mass number can be $\langle$A$\rangle\sim25$.

astro-ph.HE↗

arXiv2014

Discovery of Dramatic Optical Variability in SDSS J1100+4421: A Peculiar Radio-Loud Narrow-Line Seyfert 1 Galaxy?

We present our discovery of dramatic variability in SDSS J1100+4421 by the high-cadence transient survey Kiso Supernova Survey (KISS). The source brightened in the optical by at least a factor of three within about half a day. Spectroscopic observations suggest that this object is likely a narrow-line Seyfert 1 galaxy (NLS1) at z=0.840, however with unusually strong narrow emission lines. The estimated black hole mass of ~ 10^7 Msun implies bolometric nuclear luminosity close to the Eddington limit. SDSS J1100+4421 is also extremely radio-loud, with a radio loudness parameter of R ~ 4 x 10^2 - 3 x 10^3, which implies the presence of relativistic jets. Rapid and large-amplitude optical variability of the target, reminiscent of that found in a few radio- and gamma-ray loud NLS1s, is therefore produced most likely in a blazar-like core. The 1.4 GHz radio image of the source shows an extended structure with a linear size of about 100 kpc. If SDSS J1100+4421 is a genuine NLS1, as suggested here, this radio structure would then be the largest ever discovered in this type of active galaxies.

astro-ph.GA↗

arXiv2014

Kiso Supernova Survey (KISS): Survey Strategy

The Kiso Supernova Survey (KISS) is a high-cadence optical wide-field supernova (SN) survey. The primary goal of the survey is to catch the very early light of a SN, during the shock breakout phase. Detection of SN shock breakouts combined with multi-band photometry obtained with other facilities would provide detailed physical information on the progenitor stars of SNe. The survey is performed using a 2.2x2.2 deg field-of-view instrument on the 1.05-m Kiso Schmidt telescope, the Kiso Wide Field Camera (KWFC). We take a three-minute exposure in g-band once every hour in our survey, reaching magnitude g~20-21. About 100 nights of telescope time per year have been spent on the survey since April 2012. The number of the shock breakout detections is estimated to be of order of 1 during our 3-year project. This paper summarizes the KISS project including the KWFC observing setup, the survey strategy, the data reduction system, and CBET-reported SNe discovered so far by KISS.

astro-ph.SR↗

arXiv2014

Faint Population III supernovae as the origin of the most iron-poor stars

The most iron-deficient stars in the Milky Way provide important observational constraints on the nature of astrophysical objects that have enriched the primordial gas with heavy elements from which these stars were formed. Among them, the recently discovered iron-deficient star SMSS J031300.36-670839.3 shows a remarkable chemical composition with non-detection of iron ([Fe/H]$<-7.1$) and large enhancement of carbon and magnesium relative to calcium. We investigate the supernova yields of metal-free (Population III) stars to interpret the observed abundance pattern for this star. We report that the high [C/Ca] and [C/Mg] ratios and upper limits determined for other elemental abundances are well reproduced with the yields of core-collapse supernovae (that have normal kinetic energies of explosion $E$ of $E_{51}=E/10^{51}$erg$=1$) or hypernovae ($E_{51}\geq 10$) of the Population III 25$M_{\odot}$ or 40$M_{\odot}$ stars. The best-fit model assumes that the explosion of the Population III progenitor undergoes extensive matter mixing and fallback, leaving behind a black hole remnant. In these models, Ca is produced by static/explosive O burning and incomplete Si burning in the Population III supernova/hypernova, in contrast to the suggestion that Ca is originated from the hot CNO cycle during the presupernova evolution. Among the five most iron-poor stars with [Fe/H]$<-4.5$, four carbon-enhanced stars are consistent with the faint supernova models with the ejected mass of $^{56}$Ni less than 10$^{-3}M_{\odot}$.

astro-ph.HE↗

arXiv2014

Electron-capture supernovae exploding within their progenitor wind

The most massive stars on the asymptotic giant branch (AGB), so called super-AGB stars, are thought to produce supernovae (SNe) triggered by electron captures in their degenerate O+Ne+Mg cores. Super-AGB stars are expected to have slow winds with high mass-loss rates, so their wind density is high. The explosions of super-AGB stars are therefore presumed to occur in this dense wind. We provide the first synthetic light curves (LCs) for such events by exploding realistic electron-capture supernova (ecSN) progenitors within their super-AGB winds. We find that the early LC, i.e. before the recombination wave reaches the bottom of the H-rich envelope of SN ejecta (the plateau phase), is not affected by the dense wind. However, after the plateau phase, the luminosity remains higher when the super-AGB wind is taken into account. We compare our results to the historical LC of SN 1054, the progenitor of the Crab Nebula, and show that the explosion of an ecSN within an ordinary super-AGB wind can explain the LC features. We conclude that SN 1054 could have been a Type IIn SN without any extra extreme mass loss which was previously suggested to be necessary to account for its early high luminosity. We also show that our LCs match Type IIn SNe with an early plateau phase (`Type IIn-P') and suggest that they are ecSNe within super-AGB winds. Although some ecSNe can be bright in the optical spectral range due to the large progenitor radius, their X-ray luminosity from the interaction does not necessarily get as bright as other Type IIn SNe whose optical luminosities are also powered by the interaction. Thus, we suggest that optically-bright X-ray-faint Type IIn SNe can emerge from ecSNe. Optically-faint Type IIn SNe, such as SN 2008S, can also originate from ecSNe if their H-rich envelope masses are small. Some of them can be observed as `Type IIn-b' SNe due to the small H-rich envelope mass.

astro-ph.HE↗

arXiv2014

The Mass Spectrum of the First Stars

We perform cosmological hydrodynamics simulations with non-equilibrium primordial chemistry to obtain 59 minihalos that host first stars. The obtained minihalos are used as initial conditions of local three dimensional radiation hydrodynamics simulations to investigate the formation of the first stars. We find two-thirds of the minihalos host multiple stars, while the rest of them have single stars. The mass of the stars found in our simulations are in the range of 1 Msun \la M \la 300 Msun, peaking at several x 10 Msun. Most of the very massive stars of \ga 140 Msun are born as single stars, although not all of the single stars are very massive. We also find a few stars of \la 1 Msun that are kicked by the gravitational three body interactions to the position distant from the center of mass. The frequency that a star forming minihalo contains a binary system is \sim 50%. We also investigate the abundance pattern of the stellar remnants by summing up the contributions from the first stars in the simulations. Consequently, the pattern is compatible with that of the low metallicity Damped Lyman-alpha systems or the Extremely Metal Poor (EMP) stars, if the mass spectrum obtained in our experiment is shifted to the low mass side by 0.2 dex. If we consider the case that an EMP star is born in the remnant of the individual minihalo without mixing with others, the chemical signature of the pair instability supernova is more prominent, because most of them are born as single stars.

astro-ph.GA↗

arXiv2014

Random walks and effective optical depth in relativistic flow

We investigate the random walk process in relativistic flow. In the relativistic flow, photon propagation is concentrated in the directions of the flow velocity due to relativistic beaming effect. We show that, in the pure scattering case, the number of scatterings is proportional to the size parameter $ξ\equiv L/l_0$ if the flow velocity $β\equiv v/c$ satisfies $β/Γ\gg ξ^{-1}$, while it is proportional to $ξ^2$ if $β/Γ\ll ξ^{-1}$ where $L$ and $l_0$ are the size of the system in the observer frame and the mean free path in the comoving frame, respectively. We also examine the photon propagation in the scattering and absorptive medium. We find that, if the optical depth for absorption $τ_{\rm a}$ is considerably smaller than the optical depth for scattering $τ_{\rm s}$ ($τ_{\rm a}/τ_{\rm s} \ll 1$) and the flow velocity satisfies $β\gg \sqrt{2τ_{\rm a}/τ_{\rm s}}$, the effective optical depth is approximated by $τ_*\simeqτ_{\rm a}(1+β)/β$. Furthermore, we perform Monte Carlo simulations of radiative transfer and compare the results with the analytic expression for the number of scattering. The analytic expression is consistent with the results of the numerical simulations. The expression derived in this Letter can be used to estimate the photon production site in relativistic phenomena, e.g., gamma-ray burst and active galactic nuclei.

astro-ph.HE↗

arXiv2014

The origin of low [alpha/Fe] ratios in extremely metal-poor stars

We show that the low ratios of $α$ elements (Mg, Si, and Ca) to Fe recently found for a small fraction of extremely metal-poor stars can be naturally explained with the nucleosynthesis yields of core-collapse supernovae, i.e., $13-25M_\odot$ supernovae, or hypernovae. For the case without carbon enhancement, the ejected iron mass is normal, consistent with observed light curves and spectra of nearby supernovae. On the other hand, the carbon enhancement requires much smaller iron production, and the low [$α$/Fe] of carbon enhanced metal-poor stars can also be reproduced with $13-25M_\odot$ faint supernovae or faint hypernovae. Iron-peak element abundances, in particular Zn abundances, are important to put further constraints on the enrichment sources from galactic archaeology surveys.

astro-ph.GA↗

arXiv2014

Abundance Profiling of Extremely Metal-Poor Stars and Supernova Properties in the Early Universe

After the Big Bang nucleosynthesis, the first heavy element enrichment in the Universe was made by a supernova (SN) explosion of a population (Pop) III star (Pop III SN). The abundance ratios of elements produced from Pop III SNe are recorded in abundance patterns of extremely metal-poor (EMP) stars. The observations of the increasing number of EMP stars have made it possible to statistically constrain the explosion properties of Pop III SNe. We present Pop III SN models whose nucleosynthesis yields well-reproduce individually the abundance patterns of 48 such metal-poor stars as [Fe/H] $\mathrel{\rlap{\lower 4pt \hbox{$\sim$}}\raise 1pt \hbox {$<$}}-3.5$. We then derive relations between the abundance ratios of EMP stars and certain explosion properties of Pop III SNe: the higher [(C+N)/Fe] and [(C+N)/Mg] ratios correspond to the smaller ejected Fe mass and the larger compact remnant mass, respectively. Using these relations, the distributions of the abundance ratios of EMP stars are converted to those of the explosion properties of Pop III SNe. Such distributions are compared with those of the explosion properties of present day SNe: The distribution of the ejected Fe mass of Pop III SNe has the same peak as that of the resent day SNe but shows an extended tail down to $\sim10^{-2}-10^{-5}M_\odot$, and the distribution of the mass of the compact remnant of Pop III SNe is as wide as that of the present day stellar-mass black holes. Our results demonstrate the importance of large samples of EMP stars obtained by ongoing and future EMP star surveys and subsequent high-dispersion spectroscopic observations in clarifying the nature of Pop III SNe in the early Universe.

astro-ph.SR↗

arXiv2013

Supernova Explosions of Super-Asymptotic Giant Branch Stars: Multicolor Light Curves of Electron-Capture Supernovae

An electron-capture supernova (ECSN) is a core-collapse supernova (CCSN) explosion of a super-asymptotic giant branch (SAGB) star with a main-sequence mass $M_{\rm ms}\sim7-9.5M_\odot$. The explosion takes place in accordance with core bounce and subsequent neutrino heating and is a unique example successfully produced by first-principle simulations. This allows us to derive a first self-consistent multicolor light curves of a CCSN. Adopting the explosion properties derived by the first-principle simulation, i.e., the low explosion energy of $1.5\times10^{50}$ erg and the small $^{56}$Ni mass of $2.5\times10^{-3}M_\odot$, we perform a multigroup radiation hydrodynamics calculation of ECSNe and present multicolor light curves of ECSNe of SAGB stars with various envelope mass and hydrogen abundance. We demonstrate that a shock breakout has peak luminosity of $L\sim2\times10^{44}$ erg/s and can evaporate circumstellar dust up to $R\sim10^{17}$ cm for a case of carbon dust, that plateau luminosity and plateau duration of ECSNe are $L\sim10^{42}$ erg/s and $t\sim60-100$ days, respectively, and that a plateau is followed by a tail with a luminosity drop by $\sim4$ mag. The ECSN shows a bright and short plateau that is as bright as typical Type II plateau supernovae, and a faint tail that might be influenced by spin-down luminosity of a newborn pulsar. Furthermore, the theoretical models are compared with ECSN candidates: SN 1054 and SN 2008S. We find that SN 1054 shares the characteristics of the ECSNe. For SN 2008S, we find that its faint plateau requires an ECSN model with a significantly low explosion energy of $E\sim10^{48}$ erg.

astro-ph.HE↗

arXiv2013

Early UV/Optical Emission of The Type Ib SN 2008D

We propose an alternative explanation for the post-breakout emission of SN 2008D associated with the X-ray transient 080109. Observations of this object show a very small contrast of 0.35 dex between the light-curve minimum occurring soon after the breakout, and the main luminosity peak that is due to radioactive heating of the ejecta. Hydrodynamical models show that the cooling of a shocked Wolf-Rayet star leads to a much greater difference (> 0.9 dex). Our proposed scenario is that of a jet produced during the explosion which deposits 56Ni-rich material in the outer layers of the ejecta. The presence of high-velocity radioactive material allows us to reproduce the complete luminosity evolution of the object. Without outer 56Ni it could be possible to reproduce the early emission purely from cooling of the shocked envelope by assuming a larger progenitor than a Wolf-Rayet star, but that would require an initial density structure significantly different from what is predicted by stellar evolution models. Analytic models of the cooling phase have been proposed reproduce the early emission of SN 2008D with an extended progenitor. However, we found that the models are valid only until 1.5 days after the explosion where only two data of SN 2008D are available. We also discuss the possibility of the interaction of the ejecta with a binary companion, based on published analytic expressions. However, the binary separation required to fit the early emission should be < 3 Rsun which is too small for a system containing two massive stars.

astro-ph.SR↗

arXiv2012

Light Curve Modeling of Superluminous Supernova 2006gy: Collision between Supernova Ejecta and Dense Circumstellar Medium

We show model light curves of superluminous supernova 2006gy on the assumption that the supernova is powered by the collision of supernova ejecta and its dense circumstellar medium. The initial conditions are constructed based on the shock breakout condition, assuming that the circumstellar medium is dense enough to cause the shock breakout within it. We perform a set of numerical light curve calculations by using a one-dimensional multigroup radiation hydrodynamics code STELLA. We succeeded in reproducing the overall features of the early light curve of SN 2006gy with the circumstellar medium whose mass is about 15 Msun (the average mass-loss rate ~ 0.1 Msun/yr). Thus, the progenitor of SN 2006gy is likely a very massive star. The density profile of the circumstellar medium is not well constrained by the light curve modeling only, but our modeling disfavors the circumstellar medium formed by steady mass loss. The ejecta mass is estimated to be comparable to or less than 15 Msun and the explosion energy is expected to be more than 4e51 erg. No 56Ni is required to explain the early light curve. We find that the multidimensional effect, e.g., the Rayleigh-Taylor instability, which is expected to take place in the cool dense shell between the supernova ejecta and the dense circumstellar medium, is important in understanding supernovae powered by the shock interaction. We also show the evolution of the optical and near-infrared model light curves of high-redshift superluminous supernovae. They can be potentially used to identify SN 2006gy-like superluminous supernovae in the future optical and near-infrared transient surveys.

astro-ph.HE↗

arXiv2012

Supernovae from Red Supergiants with Extensive Mass Loss

We calculate multicolor light curves (LCs) of supernovae (SNe) from red supergiants (RSGs) exploded within dense circumstellar medium (CSM). Multicolor LCs are calculated by using a multi-group radiation hydrodynamics code STELLA. If CSM is dense enough, the shock breakout signal is delayed and smeared by CSM and kinetic energy of SN ejecta is efficiently converted to thermal energy which is eventually released as radiation. We find that explosions of RSGs are affected by CSM in early epochs when mass-loss rate just before the explosions is higher than 10^{-4} Msun/yr. Their characteristic features are that the LC has a luminous round peak followed by a flat LC, that multicolor LCs are simultaneously bright in ultraviolet and optical at the peak, and that photospheric velocity is very low at these epochs. We calculate LCs for various CSM conditions and explosion properties, i.e., mass-loss rates, radii of CSM, density slopes of CSM, explosion energies of SN ejecta, and SN progenitors inside, to see their influence on LCs. We compare our model LCs to those of ultraviolet-bright Type IIP SN 2009kf and show that the mass-loss rate of the progenitor of SN 2009kf just before the explosion is likely to be higher than 10^{-4} Msun/yr. Combined with the fact that SN 2009kf is likely to be an energetic explosion and has large 56Ni production, which implies that the progenitor of SN 2009kf is a massive RSG, our results indicate that there could be some mechanism to induce extensive mass loss in massive RSGs just before their explosions.

astro-ph.SR↗

arXiv2012

Diversity of Luminous Supernovae from Non-Steady Mass Loss

We show that the diversity in the density slope of the dense wind due to non-steady mass loss can be one way to explain the spectral diversity of Type II luminous supernovae (LSNe). The interaction of SN ejecta and wind surrounding it is considered to be a power source to illuminate LSNe because many LSNe show the wind signature in their spectra (Type IIn LSNe). However, there also exist LSNe without the spectral features caused by the wind (Type IIL LSNe). We show that, even if LSNe are illuminated by the interaction, it is possible that they do not show the narrow spectra from the wind if we take into account of non-steady mass loss of their progenitors. When the shock breakout takes place in the dense wind with the density structure ρ\propto r^{-w}, the ratio of the diffusion timescale in the optically thick region of the wind (td) and the shock propagation timescale of the entire wind after the shock breakout (ts) strongly depends on w. For the case w<~1, both timescales are comparable (td/ts \simeq 1) and td/ts gets smaller as w gets larger. For the case td/ts\simeq 1, the shock goes through the entire wind just after the light curve (LC) peak and narrow spectral lines from the wind cannot be observed after the LC peak (Type IIL LSNe). If td/ts is much smaller, the shock wave continues to propagate in the wind after the LC peak and unshocked wind remains (Type IIn LSNe). This difference can be obtained only through a careful treatment of the shock breakout condition in a dense wind. The lack of narrow Lorentzian line profiles in Type IIL LSNe before the LC peak can also be explained by the difference in the density slope. Furthermore, we apply our model to Type IIn LSN 2006gy and Type IIL LSN 2008es and find that our model is consistent with the observations.

astro-ph.HE↗

arXiv2011

Chemical Enrichment in the Carbon-enhanced Damped Lyman $α$ System

We show that the recently observed elemental abundance pattern of the carbon-rich metal-poor Damped Lyman $α$ (DLA) system is in excellent agreement with the nucleosynthesis yields of faint core-collapse supernovae of primordial stars. The observed abundance pattern is not consistent with the nucleosynthesis yields of pair-instability supernovae. The DLA abundance pattern is very similar to that of carbon-rich extremely metal-poor (EMP) stars, and the contributions from low-mass stars and/or binary effects should be very small in DLAs. This suggests that chemical enrichment by the first stars in the first galaxies is driven by core-collapse supernovae from $\sim 20-50 M_\odot$ stars, and also supports the supernova scenario as the enrichment source of EMP stars in the Milky Way Galaxy.

astro-ph.CO↗