3,588 research outputs found
On the Light Curve and Spectrum of SN 2003dh Separated from the Optical Afterglow of GRB 030329
The net optical light curves and spectra of the supernova (SN) 2003dh are
obtained from the published spectra of GRB 030329, covering about 6 days before
SN maximum to about 60 days after. The bulk of the U-band flux is subtracted
from the observed spectra using early-time afterglow templates, because strong
line blanketing greatly depresses the UV and U-band SN flux in a metal-rich,
fast-moving SN atmosphere. The blue-end spectra of the gamma-ray burst
(GRB)connected hypernova SN 1998bw is used to determine the amount of
subtraction. The subtraction of a host galaxy template affects the late-time
results. The derived SN 2003dh light curves are narrower than those of SN
1998bw, rising as fast before maximum, reaching a possibly fainter maximum, and
then declining ~ 1.2-1.4 times faster. We then build UVOIR bolometric SN light
curve. Allowing for uncertainties, it can be reproduced with a spherical ejecta
model of Mej ~ 7+/-3 Msun, KE ~ (3.5+/-1.5)E52 ergs, with KE/Mej ~ 5 following
previous spectrum modelling, and M(Ni56) ~ (0.4 +0.15/-0.1) Msun. This suggests
a progenitor main-sequence mass of about 25-40 Msun, lower than SN 1998bw but
significantly higher than normal Type Ic SNe and the GRB-unrelated hypernova SN
2002ap.Comment: 18 pages, 7 figures, published by Ap
The Connection between Gamma-Ray Bursts and Extremely Metal-Poor Stars: Black Hole-forming Supernovae with Relativistic Jets
Long-duration gamma-ray bursts (GRBs) are thought to be connected to luminous
and energetic supernovae (SNe), called hypernovae (HNe), resulting from the
black-hole (BH) forming collapse of massive stars. For recent nearby
GRBs~060505 and 060614, however, the expected SNe have not been detected. The
upper limits to the SN brightness are about 100 times fainter than
GRB-associated HNe (GRB-HNe), corresponding to the upper limits to the ejected
Ni masses of . SNe with a small
amount of Ni ejection are observed as faint Type II SNe. HNe and faint
SNe are thought to be responsible for the formation of extremely metal-poor
(EMP) stars. In this Letter, a relativistic jet-induced BH forming explosion of
the 40 star is investigated and hydrodynamic and nucleosynthetic
models are presented. These models can explain both GRB-HNe and GRBs without
bright SNe in a unified manner. Their connection to EMP stars is also
discussed. We suggest that GRBs without bright SNe are likely to synthesize
\Mni\sim 10^{-4} to or .Comment: 7 pages, 3 figures. Accepted for publication in the Astrophysical
Journal Letters (10 March 2007, v657n2 issue
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.Comment: 9 pages, 11 figures, 2 tables, accepted by The Astrophysical Journal,
proofed and some references added in v
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
A strong neutron burst in jet-like supernovae of spinstars
Some metal-poor stars have abundance patterns which are midway between the
slow (s) and rapid (r) neutron capture processes. We show that the helium shell
of a fast rotating massive star experiencing a jet-like explosion undergoes two
efficient neutron capture processes: one during stellar evolution and one
during the explosion. It eventually provides a material whose chemical
composition is midway between the s- and r-process. A low metallicity
40~ model with an initial rotational velocity of ~km~s was computed from birth to pre-supernova with a nuclear
network following the slow neutron capture process. A 2D hydrodynamic
relativistic code was used to model a ~erg relativistic jet-like
explosion hitting the stellar mantle. The jet-induced nucleosynthesis was
calculated in post-processing with a network of 1812 nuclei. During the star's
life, heavy elements from are produced thanks to an
efficient s-process, which is boosted by rotation. At the end of evolution, the
helium shell is largely enriched in trans-iron elements and in (unburnt)
Ne, whose abundance is times higher than in a non-rotating
model. During the explosion, the jet heats the helium shell up to
GK. It efficiently activates () reactions, such as
Ne(), and leads to a strong n-process with neutron densities
of ~cm during ~second. This has the effect
of shifting the s-process pattern towards heavier elements (e.g. Eu). The
resulting chemical pattern is consistent with the abundances of the
carbon-enhanced metal-poor r/s star CS29528-028, provided the ejecta of the jet
model is not homogeneously mixed. This is a new astrophysical site which can
explain at least some of the metal-poor stars showing abundance patterns midway
between the s- and r-process.Comment: 9 pages, 12 figures, accepted in A&
Experimental and Steady-RANS CFD Modelling of Cross-ventilation in Moderately-dense Urban Areas
Computational fluid dynamics (CFD) models based on the steady Reynolds-averaged Navier Stokes (SRANS) equations are vastly used for calculation of airflow field inside and around cross-ventilated buildings. However, most of the developed CFD guidelines ignore CFD challenges related to cross-ventilation modeling in terms of flow unsteadiness, high level of gradients of airflow parameters, and complex interactions between the indoor and outdoor flows.Hence, a systematic parametric study was performed in this study for a generic cross-ventilated building model with a planar area ratio of 0.25 against different wind angles while effects of different CFD parameters, including advection and diffusion terms discretization methods, mesh generation techniques, and turbulence models on prediction accuracy and convergence behavior of CFD solver were comprehensively studied.Results show that a particularly generated unstructured tetrahedral mesh configuration with significantly lower mesh numbers can provide comparable results with structured hexahedral mesh configuration. Furthermore, second-order discretization scheme for advection terms encounters convergence issues against the normal wind angle, but generally presents more accurate results against oblique wind angles. Moreover, two-equation turbulence models showed very low accuracy in the case of normal wind angle, but acceptable results were found for oblique wind angles
Nature of the Jurassic Magnetic Quiet Zone
Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 42 (2015): 8367â8372, doi:10.1002/2015GL065394.The nature of the Jurassic Quiet Zone (JQZ), a region of low-amplitude oceanic magnetic anomalies, has been a long-standing debate with implications for the history and behavior of the Earth's geomagnetic field and plate tectonics. To understand the origin of the JQZ, we studied high-resolution sea surface magnetic anomalies from the Hawaiian magnetic lineations and correlated them with the Japanese magnetic lineations. The comparison shows the following: (i) excellent correlation of anomaly shapes from M29 to M42; (ii) remarkable similarity of anomaly amplitude envelope, which decreases back in time from M19 to M38, with a minimum at M41, then increases back in time from M42; and (iii) refined locations of pre-M25 lineations in the Hawaiian lineation set. Based on these correlations, our study presents evidence of regionally and possibly globally coherent pre-M29 magnetic anomalies in the JQZ and a robust extension of Hawaiian isochrons back to M42 in the Pacific crust.National Science Foundation Grant Numbers: OCE-1029965, OCE-1233000, OCE-10295732016-04-2
Along-margin variations in breakup volcanism at the Eastern North American Margin
Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(12),(2020): e2020JB020040, https://doi.org/10.1029/2020JB020040.We model the magnetic signature of riftârelated volcanism to understand the distribution and volume of magmatic activity that occurred during the breakup of Pangaea and early Atlantic opening at the Eastern North American Margin (ENAM). Alongâstrike variations in the amplitude and character of the prominent East Coast Magnetic Anomaly (ECMA) suggest that the emplacement of the volcanic layers producing this anomaly similarly varied along the margin. We use threeâdimensional magnetic forward modeling constrained by seismic interpretations to identify alongâmargin variations in volcanic thickness and width that can explain the observed amplitude and character of the ECMA. Our model results suggest that the ECMA is produced by a combination of both firstâorder (~600â1,000 km) and secondâorder (~50â100 km) magmatic segmentation. The firstâorder magmatic segmentation could have resulted from preexisting variations in crustal thickness and rheology developed during the tectonic amalgamation of Pangaea. The secondâorder magmatic segmentation developed during continental breakup and likely influenced the segmentation and transform fault spacing of the initial, and modern, MidâAtlantic Ridge. These variations in magmatism show how extension and thermal weakening was distributed at the ENAM during continental breakup and how this breakup magmatism was related to both previous and subsequent Wilson cycle stages.Thanks to Anne BĂ©cel, Dan Lizarralde, Collin Brandl, Brandon Shuck, and Mark Everett for beneficial discussion and assistance in compiling the archived data used in this study. We thank Debbie Hutchinson (USGS Woods Hole Coastal and Marine Science Center) for passing along her vast breadth of knowledge on the ENAM through numerous constructive suggestions to greatly strengthen our manuscript. We greatly appreciate the insightful comments from two reviewers, the Associate Editor, and the Editor that significantly improved the manuscript. Thanks to Maurice Tivey for providing codes that aided our magnetic modeling efforts. Project completed as part of J.A.G.'s Ph.D. dissertation at Texas A&M University.2021-05-1
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