arXiv subjects

Keiichi Maeda

Publications and source records attributed to Keiichi Maeda.

At least 235 records · Page 13Linked to original sources

arXiv2013

Integral field spectroscopy of supernova explosion sites: constraining mass and metallicity of the progenitors - I. Type Ib and Ic supernovae

Integral field spectroscopy of 11 type-Ib/c supernova explosion sites in nearby galaxies has been obtained using UH88/SNIFS and Gemini-N/GMOS. The use of integral field spectroscopy enables us to obtain both spatial and spectral information of the explosion site, allowing the identification of the parent stellar population of the supernova progenitor star. The spectrum of the parent population provides metallicity determination via strong-line method and age estimation obtained via comparison with simple stellar population (SSP) models. We adopt this information as the metallicity and age of the supernova progenitor, under the assumption that it was coeval with the parent stellar population. The age of the star corresponds to its lifetime, which in turn gives the estimate of its initial mass. With this method we were able to determine both the metallicity and initial (ZAMS) mass of the progenitor stars of the type Ib and Ic supernovae. We found that on average SN Ic explosion sites are more metal-rich and younger than SN Ib sites. The initial mass of the progenitors derived from parent stellar population age suggests that SN Ic have more massive progenitors than SN Ib. In addition, we also found indication that some of our SN progenitors are less massive than ~25 Msun, indicating that they may have been stars in a close binary system that have lost their outer envelope via binary interactions to produce Ib/c supernovae, instead of single Wolf-Rayet stars. These findings support the current suggestions that both binary and single progenitor channels are in effect in producing type Ib/c supernovae. This work also demonstrates the power of integral field spectroscopy in investigating supernova environments and active star forming regions.

astro-ph.CO↗

arXiv2013

Extraordinary Magnification of the Ordinary Type Ia Supernova PS1-10afx

Recently, Chornock and co-workers announced the Pan-STARRS discovery of a transient source reaching an apparent peak luminosity of ~4x10^44 erg s^-1. We show that the spectra of this transient source are well fit by normal Type Ia supernova (SNIa) templates. The multi-band colors and light-curve shapes are also consistent with normal SNeIa at the spectroscopically determined redshift of z=1.3883; however, the observed flux is a constant factor of ~30 times too bright in each band over time as compared to the templates. At minimum, this shows that the peak luminosities inferred from the light-curve widths of some SNeIa will deviate significantly from the established, empirical relation used by cosmologists. We argue on physical grounds that the observed fluxes do not reflect an intrinsically luminous SNIa, but rather PS1-10afx is a normal SNIa whose flux has been magnified by an external source. The only known astrophysical source capable of such magnification is a gravitational lens. Given the lack of obvious lens candidates, such as galaxy clusters, in the vicinity, we further argue that the lens is a supermassive black hole or a comparatively low-mass dark matter halo. In this case, the lens continues to magnify the underlying host galaxy light. If confirmed, this discovery could impact a broad range of topics including cosmology, gamma-ray bursts, and dark matter halos.

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arXiv2012

Probing Shock Breakout and Progenitors of Stripped-Envelope Supernovae through Their Early Radio Emissions

We study properties of early radio emission from stripped-envelope supernovae (those of type IIb/Ib/Ic). We suggest there is a sub-class of stripped-envelope supernovae in their radio properties, including optically well-studied type Ic supernovae (SNe Ic) 2002ap and 2007gr, showing a rapid rise to a radio peak within ~ 10 days reaching to a low luminosity (at least an order of magnitude fainter than a majority of SNe IIb/Ib/Ic). They show a decline after the peak shallower than others while the spectral index is similar. We show that all these properties are naturally explained if the circumstellar material (CSM) density is low and therefore the forward shock is expanding into the CSM without deceleration. Since the forward shock velocity in this situation, as estimated from the radio properties, still records the maximum velocity of the SN ejecta following the shock breakout, observing these SNe in radio wavelengths provides new diagnostics on natures of the breakout and progenitor which otherwise requires a quite rapid follow-up in other wavelengths. The inferred post-shock breakout velocities of SNe Ic 2002ap and 2007gr are sub-relativistic, ~0.3c. These are higher than inferred for SN II 1987A, in line with suggested compact progenitors. However, these are lower than expected for a Wolf-Rayet (WR) progenitor. It may reflect a still-unresolved nature of the progenitors just before the explosion, and we suggest that the WR progenitor envelopes might have been inflated which could quickly reduce the maximum ejecta velocity from the initial shock breakout velocity.

astro-ph.HE↗

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.

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arXiv2012

A theoretical color-velocity correlation for supernovae associated with gamma-ray bursts

We carry out the first multi-dimensional radiative transfer calculations to simultaneously compute synthetic spectra and light curves for models of supernovae driven by fast bipolar outflows. These allow us to make self-consistent predictions for the orientation dependence of both colour evolution and spectral features. We compare models with different degrees of asphericity and metallicity and find significant observable consequences of both. In aspherical models, we find spectral and light curve features that vary systematically with observer orientation. In particular, we find that the early phase light curves are brighter and bluer when viewed close to the polar axis but that the peak flux is highest for equatorial (off-axis) inclinations. Spectral line features also depend systematically on observer orientation, including the velocity of the SiII 6355A line. Consequently, our models predict a correlation between line velocity and color that could assist the identification of supernovae associated with off-axis jet-driven explosions. The amplitude and range of this correlation depends on the degree of asphericity, the metallicity and the epoch of observation but we find that it is always present and acts in the same direction.

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arXiv2012

Injection and Acceleration of Electrons at A Strong Shock: Radio and X-ray Study of Young Supernova 2011dh

In this paper, we develop a model for the radio and X-ray emissions from Type IIb Supernova (SN IIb) 2011dh in the first 100 days after the explosion, and investigate a spectrum of relativistic electrons accelerated at a strong shock wave. The widely-accepted theory of the particle acceleration, so-called diffusive shock acceleration (DSA) or Fermi mechanism, requires seed electrons with modest energy with gamma ~ 1 - 100, and little is known about this pre-acceleration mechanism: We derive the energy distribution of relativistic electrons in this pre-accelerated energy regime. We find that the efficiency of the electron acceleration must be low, i.e., epsilon_e <~ 0.01 as compared to the conventionally assumed value of epsilon_e ~ 0.1. Furthermore, independently from the low value of epsilon_e, we find that the X-ray luminosity cannot be attributed to any emission mechanisms suggested so far as long as these electrons follow the conventionally-assumed single power-law distribution. A consistent view between the radio and X-ray can only be obtained if the pre-acceleration injection spectrum peaks at gamma ~ 20-30 and then only a fraction of these electrons eventually experience the DSA-like acceleration toward the higher energy -- then the radio and X-ray properties are explained through the synchrotron and inverse Compton mechanisms, respectively. Our findings support the idea that the pre-acceleration of the electrons is coupled with the generation/amplification of the magnetic field.

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arXiv2012

A Dip after the Early Emission of Super-Luminous Supernovae: A Signature of Shock Breakout within Dense Circumstellar Media

The origin of super-luminous supernovae (SLSNe), especially the source of their huge luminosities, has not been clarified yet. While a strong interaction between SN ejecta and dense circumstellar media (CSM) is a leading scenario, alternative models have been proposed. In this Letter, we suggest new diagnostics to discriminate the strong SN-CSM interaction scenario from the others: a decline in the luminosity ('dip') before the main peak of the light curve. This dip is an unavoidable consequence of having a dense CSM within which the shock breakout occurs. If a dense CSM shell is located far at large radii from the progenitor inside, it takes time for the SN ejecta to reach it and the early light curve can be powered by the SN ejecta before the collision. Once the SN ejecta collides with the dense CSM, the electron density and thus the Thomson scattering opacity suddenly increase. Photons become unable to go out of the shock even if there is a source of emission inside, which results in the dip in the light curve. This dip is a solid prediction from the strong interaction scenario irrespective of a power source for the early emission. Eventually the forward shock breaks out from within the dense CSM, and the luminosity increases by the continuous strong SN-CSM interaction, resulting in an SLSN. The possible dip observed in the hydrogen-poor SLSN, 2006oz, could be the first example of this signature and give support to the SN-CSM interaction as the power source of SLSN 2006oz.

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arXiv2012

The Type IIb Supernova 2011dh from a Supergiant Progenitor

A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star ---with R ~200 Rsun---, is needed to reproduce the early light curve of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the SN in deep pre-explosion images is the progenitor star. From the main peak of the bolometric light curve and expansion velocities we constrain the mass of the ejecta to be ~2 Msun, the explosion energy to be E= 6-10 x 10^50 erg, and the 56Ni mass to be approximately 0.06 Msun. The progenitor star was composed of a helium core of 3 to 4 Msun and a thin hydrogen-rich envelope of ~0.1 M_sun with a main sequence mass estimated to be in the range of 12--15 Msun. Our models rule out progenitors with helium-core masses larger than 8 Msun, which correspond to M_ZAMS > 25 Msun. This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

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arXiv2012

Three-Dimensional Explosion Geometry of Stripped-Envelope Core-Collapse Supernovae. I. Spectropolarimetric Observations

We study the multi-dimensional geometry of supernova (SN) explosions by means of spectropolarimetric observations of stripped-envelope SNe, i.e., SNe without a H-rich layer. We perform spectropolarimetric observations of 2 stripped-envelope SNe, the Type Ib SN 2009jf and the Type Ic SN 2009mi. Both objects show non-zero polarization at the wavelength of the strong lines. They also show a loop in the Stokes Q-U diagram, which indicates a non-axisymmetric, three-dimensional ion distribution in the ejecta. We show that five out of six stripped-envelope SNe which have been observed spectropolarimetrically so far show such a loop. This implies that a three-dimensional geometry is common in stripped-envelope SNe. We find that stronger lines tend to show higher polarization. This effect is not related to the geometry, and must be corrected to compare the polarization of different lines or different objects. Even after the correction, however, there remains a dispersion of polarization degree among different objects. Such a dispersion might be caused by three-dimensional clumpy ion distributions viewed from different directions.

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arXiv2012

The Highly Energetic Expansion of SN2010bh Associated with GRB 100316D

We present the spectroscopic and photometric evolution of the nearby (z = 0.059) spectroscopically confirmed type Ic supernova, SN 2010bh, associated with the soft, long-duration gamma-ray burst (X-ray flash) GRB 100316D. Intensive follow-up observations of SN 2010bh were performed at the ESO Very Large Telescope (VLT) using the X-shooter and FORS2 instruments. Owing to the detailed temporal coverage and the extended wavelength range (3000--24800 A), we obtained an unprecedentedly rich spectral sequence among the hypernovae, making SN 2010bh one of the best studied representatives of this SN class. We find that SN 2010bh has a more rapid rise to maximum brightness (8.0 +/- 1.0 rest-frame days) and a fainter absolute peak luminosity (L_bol~3e42 erg/s) than previously observed SN events associated with GRBs. Our estimate of the ejected (56)Ni mass is 0.12 +/- 0.02 Msun. From the broad spectral features we measure expansion velocities up to 47,000 km/s, higher than those of SNe 1998bw (GRB 980425) and 2006aj (GRB 060218). Helium absorption lines He I lambda5876 and He I 1.083 microm, blueshifted by ~20,000--30,000 km/s and ~28,000--38,000 km/s, respectively, may be present in the optical spectra. However, the lack of coverage of the He I 2.058 microm line prevents us from confirming such identifications. The nebular spectrum, taken at ~186 days after the explosion, shows a broad but faint [O I] emission at 6340 A. The light-curve shape and photospheric expansion velocities of SN 2010bh suggest that we witnessed a highly energetic explosion with a small ejected mass (E_k ~ 1e52 erg and M_ej ~ 3 Msun). The observed properties of SN 2010bh further extend the heterogeneity of the class of GRB supernovae.

astro-ph.HE↗

arXiv2012

A Search for Infrared Emission from Core-Collapse Supernovae at the Transitional Phase

Most of the observational studies of supernova (SN) explosions are limited to early phases (< a few yr after the explosion) of extragalactic SNe and observations of SN remnants (> 100 yr) in our Galaxy or very nearby galaxies. SNe at the epoch between these two, which we call "transitional" phase, have not been explored in detail except for several extragalactic SNe including SN 1987A in the Large Magellanic Cloud. We present theoretical predictions for the infrared (IR) dust emissions by several mechanisms; emission from dust formed in the SN ejecta, light echo by circumstellar and interstellar dust, and emission from shocked circumstellar dust. We search for IR emission from 6 core-collapse SNe at the transitional phase in the nearby galaxies NGC 1313, NGC 6946, and M101 by using the data taken with the AKARI satellite and Spitzer. Among 6 targets, we detect the emission from SN 1978K in NGC 1313. SN 1978K is associated with 1.3 x 10^{-3} Msun of silicate dust. We show that, among several mechanisms, the shocked circumstellar dust is the most probable emission source to explain the IR emission observed for CSM-rich SN 1978K. IR emission from the other 5 objects is not detected. Our current observations are sensitive to IR luminosity of > 10^{38} erg s^{-1}, and the non-detection of SN 1962M excludes the existence of the shocked circumstellar dust for a high gas mass-loss rate of sim 10^{-4} Msun yr^{-1}. Observations of SNe at the transitional phase with future IR satellites will fill the gap of IR observations of SNe with the age of 10-100 years, and give a new opportunity to study the circumstellar and interstellar environments of the progenitor, and possibly dust formation in SNe.

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arXiv2012

Elemental Abundances in the Possible Type Ia Supernova Remnant G344.7-0.1

Recent studies on the Galactic supernova remnant (SNR) G344.7-0.1 have commonly claimed its origin to be a core-collapse supernova (SN) explosion, based on its highly asymmetric morphology and/or proximity to a star forming region. In this paper, however, we present an X-ray spectroscopic study of this SNR using Suzaku, which is supportive of a Type Ia origin. Strong K-shell emission from lowly ionized Fe has clearly been detected, and its origin is determined, for the first time, to be the Fe-rich SN ejecta. The abundance pattern is highly consistent with that expected for a somewhat-evolved Type Ia SNR. It is suggested, therefore, that the X-ray point-like source CXOU J170357.8-414302 located at the SNR's geometrical center is not associated with the SNR but is likely to be a foreground object. Our result further indicates that G344.7-0.1 is the first possible Type Ia SNR categorized as a member of the so-called "mixed-morphology" class. In addition, we have detected emission from He-like Al at ~1.6 keV, the first clear detection of this element in the spectrum of an extended X-ray source. The possible enhancement of the Al/Mg abundance ratio from the solar value suggests that the ambient interstellar medium has a relatively high metallicity (not less than 10% of the solar value), if this SNR has indeed a Type Ia origin. We also report marginal detection of Cr and Mn, although the measured fluxes have large statistical and systematic uncertainties.

astro-ph.HE↗

arXiv2011

Unburned Material in the Ejecta of Type Ia Supernovae

(Abridged) The presence of unburned material in the ejecta of normal Type Ia supernovae (SNeIa) is investigated using early-time spectroscopy obtained by the CSP. The tell-tale signature of pristine material from a C+O white dwarf progenitor star is the presence of carbon. The most prominent carbon lines in optical spectra of SNeIa are due to C II. We find that at least 30% of the objects in the sample show an absorption at ~6300 AA which is attributed to C II 6580. An association to H_alpha is considered to be unlikely. These findings imply a larger incidence of carbon in SNeIa ejecta than previously noted. We show how observational biases and physical conditions may hide these C II lines, and account for the scarcity of previous carbon detections. This relatively large frequency of carbon detections has crucial implications on our understanding of the explosive process. The observations indicate that carbon is present merely ~1000 km s^-1 above the bulk of Si II. Spectral modeling shows the detections are consistent with a mass of carbon of 10^-3--10^-2 M_sun. This would imply substantial mixing, which may be related to asymmetries of the flame propagation or clumps of unburned material along the line of sight. However, the uniformity of the relation between C II and Si II velocities is not consistent with the latter scenario. The observational properties of SNeIa with and without carbon signatures are compared. A trend toward bluer color and lower luminosity is found for objects with carbon.

astro-ph.CO↗

arXiv2011

A study of the color diversity around maximum light in Type Ia supernovae

From a sample of 12 well-observed Type Ia supernovae, we find clear evidence of correlations between early phase (U-B), (V-R), and (V-I) colors and the velocity shifts of the [Fe II] λ7155 and [Ni II] λ7378 nebular lines measured from late-phase spectra. As these lines are thought to trace the ashes of the initial deflagration process, our findings provide additional support to the new paradigm of off-center explosions in Type Ia supernovae, and we interpret these correlations as viewing angle effects in the observed colors. We also show that the nebular velocity shifts are related to the strength and width of the Ca II H&K and IR-triplet lines near-maximum light. The evidence presented here implies that the viewing angle must be taken into account when deriving extinction values and distances in future cosmological studies based on Type Ia supernovae.

astro-ph.CO↗

arXiv2011

On the effects of microphysical grain properties on the yields of carbonaceous dust from type II SNe

We study the role of the unknown microphysical properties of carbonaceous dust particles in determining the amount and size distribution of carbonaceous dust condensed in type II supernova explosions. We parametrize the microphysical properties in terms of the shape factor of the grain and the sticking coefficient of gas-phase carbon atoms onto the grain surfaces. We find that the amount of dust formed is fairly independent of these properties, within the parameter range considered, though limited by the available amount of carbon atoms not locked in CO molecules. However, we find that the condensation times and size distributions of dust grains depend sensitively on the microphysical parameters, with the mass distributions being weighted toward larger effective radii for conditions considering grains with higher sticking coefficients and/or more aspherical shapes. We discuss that this leads to important consequences on the predicted extinction law of SN dust and on the survival rate of the formed grains as they pass through the reverse shock of the SN. We conclude that a more detailed understanding of the dust formation process and of the microphysical properties of each dust species needs to be achieved before robust prediction on the SN dust yields can be performed.

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arXiv2011

Formation of Dust in the Ejecta of Type Ia Supernovae

We investigate the formation of dust grains in the ejecta of Type Ia supernovae (SNe Ia), adopting the carbon-deflagration W7 model. In the calculations of dust formation, we apply the nucleation and grain growth theory and consider the two cases with and without formation of CO and SiO molecules. The results of the calculations show that for the sticking probability of alpha_j=1, C, silicate, Si, and FeS grains can condense at early times of ~100--300 days after the explosion, whereas Fe and SiC grains cannot form substantially. Due to the low gas density in SNe Ia with no H-envelope, the average radii of the newly formed grains are generally below 0.01 micron, being much smaller than those in Type II-P SNe. This supports our previous conclusion that the radius of dust formed in the ejecta is smaller in SNe with less massive envelopes. The total dust mass ranges from 3x10^{-4} M_sun to 0.2 M_sun for alpha_j=0.1--1, depending on whether or not CO and SiO molecules are formed. We also estimate the optical depths and thermal emission by the newly formed dust and compare to the relevant observations of SNe Ia. We find that the formation of C grains in SNe Ia is suppressed to be consistent with the observational constraints. This implies that energetic photons and electrons heavily depress the formation efficiency of C grains or that the outermost C-O layer of SNe Ia is almost fully burned. Finally, we perform the calculations of dust destruction in the SN remnants and find that dust grains formed in the ejecta of SNe Ia are almost completely destroyed in the shocked gas before being injected into the interstellar medium. This indicates that SNe Ia are unlikely to be the major sources of interstellar dust.

astro-ph.SR↗

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.

astro-ph.HE↗

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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