1,346 research outputs found
The Unique Type Ib Supernova 2005bf at Nebular Phases: A Possible Birth Event of A Strongly Magnetized Neutron Star
Late phase nebular spectra and photometry of Type Ib Supernova (SN) 2005bf
taken by the Subaru telescope at ~ 270 and ~ 310 days since the explosion are
presented. Emission lines ([OI]6300, 6363, [CaII]7291, 7324, [FeII]7155) show
the blueshift of ~ 1,500 - 2,000 km s-1. The [OI] doublet shows a doubly-peaked
profile. The line luminosities can be interpreted as coming from a blob or jet
containing only ~ 0.1 - 0.4 Msun, in which ~ 0.02 - 0.06 Msun is 56Ni
synthesized at the explosion. To explain the blueshift, the blob should either
be of unipolar moving at the center-of-mass velocity v ~ 2,000 - 5,000 km s-1,
or suffer from self-absorption within the ejecta as seen in SN 1990I. In both
interpretations, the low-mass blob component dominates the optical output both
at the first peak (~ 20 days) and at the late phase (~ 300 days). The low
luminosity at the late phase (the absolute R magnitude M_R ~ -10.2 mag at ~ 270
days) sets the upper limit for the mass of 56Ni < ~ 0.08 Msun, which is in
contradiction to the value necessary to explain the second, main peak
luminosity (M_R ~ -18.3 mag at ~ 40 days). Encountered by this difficulty in
the 56Ni heating model, we suggest an alternative scenario in which the heating
source is a newly born, strongly magnetized neutron star (a magnetar) with the
surface magnetic field Bmag ~ 10^{14-15} gauss and the initial spin period P0 ~
10 ms. Then, SN 2005bf could be a link between normal SNe Ib/c and an X-Ray
Flash associated SN 2006aj, connected in terms of Bmag and/or P0.Comment: 16 pages, 12 figures. Accepted by the Astrophysical Journa
Charmonium dissociation temperatures in lattice QCD with a finite volume technique
Dissociation temperatures of J/\psi, \psi', and \chi_c states play key roles
in the sequential J/\psi suppression scenario for high energy heavy ion
collisions. We report on a study of charmonium dissociation temperatures in
quenched lattice QCD. On anisotropic lattices, we first subtract the effects of
the constant mode in finite temperature meson correlators, which have lead to
unphysical results in previous studies. We then extract ground and first exited
state masses by diagonalizing correlation functions among different source and
sink operators. To distinguish bound states from scattering states, we first
compare the charmonium mass spectra under different spatial boundary
conditions, and examine the shape and the volume-dependence of their
Bethe-Salpeter wave functions. From these studies, we found so far no sign of
scattering states up to about 2.3T_c.Comment: 4pages, 2figures, proceedings of Quark Matter 2008 (QM2008), Jaipur,
India, Feb 4-10, 200
Full particle simulation of a perpendicular collisionless shock: A shock-rest-frame model
The full kinetic dynamics of a perpendicular collisionless shock is studied
by means of a one-dimensional electromagnetic full particle simulation. The
present simulation domain is taken in the shock rest frame in contrast to the
previous full particle simulations of shocks. Preliminary results show that the
downstream state falls into a unique cyclic reformation state for a given set
of upstream parameters through the self-consistent kinetic processes.Comment: 4 pages, 2 figures, published in "Earth, Planets and Space" (EPS),
the paper with full resolution images is
http://theo.phys.sci.hiroshima-u.ac.jp/~ryo/papers/shock_rest.pd
Hypernova Nucleosynthesis and Galactic Chemical Evolution
We study nucleosynthesis in 'hypernovae', i.e., supernovae with very large
explosion energies ( \gsim 10^{52} ergs) for both spherical and aspherical
explosions. The hypernova yields compared to those of ordinary core-collapse
supernovae show the following characteristics: 1) Complete Si-burning takes
place in more extended region, so that the mass ratio between the complete and
incomplete Si burning regions is generally larger in hypernovae than normal
supernovae. As a result, higher energy explosions tend to produce larger [(Zn,
Co)/Fe], small [(Mn, Cr)/Fe], and larger [Fe/O], which could explain the trend
observed in very metal-poor stars. 2) Si-burning takes place in lower density
regions, so that the effects of -rich freezeout is enhanced. Thus
Ca, Ti, and Zn are produced more abundantly than in normal
supernovae. The large [(Ti, Zn)/Fe] ratios observed in very metal poor stars
strongly suggest a significant contribution of hypernovae. 3) Oxygen burning
also takes place in more extended regions for the larger explosion energy. Then
a larger amount of Si, S, Ar, and Ca ("Si") are synthesized, which makes the
"Si"/O ratio larger. The abundance pattern of the starburst galaxy M82 may be
attributed to hypernova explosions. Asphericity in the explosions strengthens
the nucleosynthesis properties of hypernovae except for "Si"/O. We thus suggest
that hypernovae make important contribution to the early Galactic (and cosmic)
chemical evolution.Comment: To be published in "The Influence of Binaries on Stellar Population
Studies", ed. D. Vanbeveren (Kluwer), 200
Heavy Quark Diffusion and Lattice Correlators
We study charmonia correlators at finite temperature. We analyze to what
extent heavy quarkonia correlators are sensitive to the effect of heavy quark
transport and whether it is possible to constrain the heavy quark diffusion
constant by lattice calculations. Preliminary lattice calculations of quarkonia
correlators performed on anisotropic lattices show that they are sensitive to
the effect of heavy quark transport, but much detailed calculations are
required to constrain the value of the heavy quark diffusion constant.Comment: Based on talks presented on Lattice 2005, Extreme QCD 2005 and Quark
Matter 2005, 5 pages, 4 Figure
Nucleosynthesis in Black-Hole-Forming Supernovae and Abundance Patterns of Extremely Metal-Poor Stars
Stars more massive than 20 - 25 \ms form a black hole at the end of
their evolution. Stars with non-rotating black holes are likely to collapse
"quietly" ejecting a small amount of heavy elements (Faint supernovae). In
contrast, stars with rotating black holes are likely to give rise to very
energetic supernovae (Hypernovae). We present distinct nucleosynthesis features
of these two types of "black-hole-forming" supernovae. Nucleosynthesis in
Hypernovae is characterized by larger abundance ratios (Zn,Co,V,Ti)/Fe and
smaller (Mn,Cr)/Fe than normal supernovae, which can explain the observed trend
of these ratios in extremely metal-poor stars. Nucleosynthesis in Faint
supernovae is characterized by a large amount of fall-back. We show that the
abundance pattern of the recently discovered most Fe-poor star, HE0107-5240,
and other extremely metal-poor carbon-rich stars are in good accord with those
of black-hole-forming supernovae, but not pair-instability supernovae. This
suggests that black-hole-forming supernovae made important contributions to the
early Galactic (and cosmic) chemical evolution. Finally we discuss the nature
of First (Pop III) Stars.Comment: 12 pages, 9 figures. To appear in "Carnegie Observatories
Astrophysics Series, Vol. 4: Origin and Evolution of the Elements, 2003, eds.
A. McWilliam and M. Rauch (Pasadena: Carnegie Observatories
The Spatial String Tension and Dimensional Reduction in QCD
We calculate the spatial string tension in (2+1) flavor QCD with physical
strange quark mass and almost physical light quark masses using lattices with
temporal extent N_tau=4,6 and 8. We compare our results on the spatial string
tension with predictions of dimensionally reduced QCD. This suggests that also
in the presence of light dynamical quarks dimensional reduction works well down
to temperatures 1.5T_c.Comment: 8 pages ReVTeX, 4 figure
The Unique Type Ib Supernova 2005bf: A WN Star Explosion Model for Peculiar Light Curves and Spectra
Observations and modeling for the light curve (LC) and spectra of supernova
(SN) 2005bf are reported. This SN showed unique features: the LC had two
maxima, and declined rapidly after the second maximum, while the spectra showed
strengthening He lines whose velocity increased with time. The double-peaked LC
can be reproduced by a double-peaked Ni distribution, with most
Ni at low velocity and a small amount at high velocity. The rapid
post-maximum decline requires a large fraction of the -rays to escape
from the Ni-dominated region, possibly because of low-density ``holes''.
The presence of Balmer lines in the spectrum suggests that the He layer of the
progenitor was substantially intact. Increasing -ray deposition in the
He layer due to enhanced -ray escape from the Ni-dominated
region may explain both the delayed strengthening and the increasing velocity
of the He lines. The SN has massive ejecta (\sim6-7\Msun), normal kinetic
energy ( ergs), high peak bolometric luminosity
( erg s) for an epoch as late as 40 days,
and a large Ni mass (\sim0.32\Msun). These properties, and the
presence of a small amount of H suggest that the progenitor was initially
massive (M\sim 25-30 \Msun) and had lost most of its H envelope, and was
possibly a WN star. The double-peaked Ni distribution suggests that the
explosion may have formed jets that did not reach the He layer. The properties
of SN 2005bf resemble those of the explosion of Cassiopeia A.Comment: 10 pages, 4 figures. Figure of UBVr'i'JHKs light curves is revised.
Accepted for publication in the Astrophysical Journal (Letters) on 5 October
200
On the Relation Between Peak Luminosity and Parent Population of Type Ia Supernovae: A New Tool for Probing the Ages of Distant Galaxies
We study the properties of Type Ia Supernovae (SNe Ia) as functions of the
radial distance from their host galaxy centers. Using a sample of 62 SNe Ia
with reliable luminosity, reddening, and decline rate determinations, we find
no significant radial gradients of SNe Ia peak absolute magnitudes or decline
rates in elliptical+S0 galaxies, suggesting that the diversity of SN properties
is not related to the metallicity of their progenitors. We do find that the
range in brightness and light curve width of supernovae in spiral galaxies
extends to brighter, broader values. These results are interpreted as support
for an age, but not metallicity, related origin of the diversity in SNe Ia. If
confirmed with a larger and more accurate sample of data, the age-luminosity
relation would offer a new and powerful tool to probe the ages and age
gradients of stellar populations in galaxies at redshift as high as .
The absence of significant radial gradients in the peak and colors of SNe Ia supports the redding correction method of Phillips et
al (1999). We find no radial gradient in residuals from the SN Ia
luminosity-width relation, suggesting that the relation is not affected by
properties of the progenitor populations and supporting the reliability of
cosmological results based upon the use of SNe Ia as distance indicators.Comment: 19 pages, incl. 3 tables & 3 figures; to appear in Nov 2000 issue of
Ap
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