114 research outputs found
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.Comment: 10 pages, 10 figures, Accepted for publication in Ap
強度変調放射線治療計画の線量体積制約に基づく最適化
We present a novel optimization method to handle dose-volume constraints (DVCs) directly in intensity-modulated radiation therapy (IMRT) treatment planning based on the idea of continuous dynamical methods. Most of the conventional methods are constructed for solving inconsistent inverse problems with, e.g., dose-volume based objective functions, and one expects to obtain a feasible solution that minimally violates the DVCs. We introduce the concept of ‘acceptable’, meaning that there exists a nonempty set of radiation beam weights satisfying the given DVCs, and we resolve the issue that the objective and evaluation are different in the conventional planning approach. We apply the initial-value problem of the proposed dynamical system to an acceptable and inconsistent inverse problem and prove that the convergence to an equilibrium in the acceptable set of solutions is theoretically guaranteed by using the Lyapunov theorem. Indeed, we confirmed that we can obtain acceptable beam weights through numerical experiments using phantom data simulating a clinical setup for an acceptable and inconsistent IMRT planning system
The evolution of the peculiar Type Ia supernova SN 2005hk over 400 days
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.Comment: Accepted for publication in The Astrophysical Journal. Minor
revision, discussion section adde
Development of a Si/CdTe semiconductor Compton telescope
We are developing a Compton telescope based on high resolution Si and CdTe
imaging devices in order to obtain a high sensitivity astrophysical observation
in sub-MeV gamma-ray region. In this paper, recent results from the prototype
Si/CdTe semiconductor Compton telescope are reported. The Compton telescope
consists of a double-sided Si strip detector (DSSD) and CdTe pixel detectors,
combined with low noise analog LSI, VA32TA. With this detector, we obtained
Compton reconstructed images and spectra from line gamma-rays ranging from 81
keV up to 356 keV. The energy resolution is 3.8 keV and 7.9 keV at 122 keV and
356 keV, respectively, and the angular resolution is 9.9 degrees and 5.7
degrees at 122 keV and 356 keV, respectively.Comment: 12 pages, 14 figures, submitted to SPIE conference proceedings vol.
5501, "High-Energy Detectors in Astronomy", Glasgow UK, 6/21-6/24 200
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.Comment: 7 pages, 5 figure
Spectropolarimetry of Extremely Luminous Type Ia Supernova 2009dc: Nearly Spherical Explosion of Super-Chandrasekhar Mass White Dwarf
We present the first spectropolarimetric observations of a candidate of
super-Chandrasekhar mass Type Ia supernova (SN): SN 2009dc. The observations
were performed at 5.6 and 89.5 days after the B-band maximum. The data taken at
the later epoch are used to determine the interstellar polarization. Continuum
polarization is found to be small (<0.3 %), indicating that the explosion is
nearly spherically symmetric. This fact suggests that a very aspherical
explosion is not a likely scenario for SN 2009dc. Polarization at the Si II and
Ca II lines clearly shows a loop in the Q-U plane, indicating a
non-axisymmetric, clumpy distribution of intermediate-mass elements. The degree
of line polarization at the Si and Ca line is moderate (0.5% +- 0.1% and 0.7%
+- 0.1%, respectively), but it is higher than expected from the trend of other
Type Ia SNe. This may suggest that there are thick enough, clumpy Si-rich
layers above the thick 56Ni-rich layers (>~ 1.2 Msun). The observed
spectropolarimetric properties, combined with the photometric and spectroscopic
properties, suggest that the progenitor of SN 2009dc has a super-Chandrasekhar
mass, and that the explosion geometry is globally spherically symmetric, with
clumpy distribution of intermediate-mass elements.Comment: 9 pages, 6 figures, The Astrophysical Journal, in pres
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