2,466 research outputs found
Precursors and Main-bursts of Gamma Ray Bursts in a Hypernova Scenario
We investigate a "hypernova" model for gamma-ray bursts (GRBs), i.e., massive
C+O star model with relativistic jets. In this model, non-thermal precursors
can be produced by the "first" relativistic shell ejected from the star. Main
GRBs are produced behind the "first"-shell by the collisions of several
relativistic shells. They become visible to distant observers after the
colliding region becomes optically thin. We examine six selected conditions
using relativistic hydrodynamical simulations and simple analyses.
Interestingly, our simulations show that sub-relativistic jets
from the central engine is sufficient to produce highly-relativistic shells. We find that the relativistic shells from such a star can
reproduce observed GRBs with certain conditions. Two conditions are especially
important. One is the sufficiently long duration of the central engine \gsim
100 sec. The other is the existence of a dense-shell somewhere behind the
"first"-shell. Under these conditions, both the existence and non-existence of
precursors, and long delay between precursors and main GRBs can be explained.Comment: 8 pages, 2 figures. Accepted for publication in the Astrophysical
Journal (Letters
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
Quantum-electrodynamical treatment of second-harmonic generation through phase-conjugate six-wave mixing: Temporal analysis
Review of CFD Guidelines for Dispersion Modeling
This is the review of CFD (Computational Fluid Dynamics) guidelines for dispersion modeling in the USA, Japan and Germany. Most parts of this review are based on the short report of the special meeting on CFD Guidelines held at the International Symposium on Computational Wind Engineering (CWE2014), University of Hamburg, June 2014. The objective of this meeting was to introduce and discuss the action program to make worldwide guidelines of CFD gas-dispersion modeling. The following six gas-dispersion guidelines including Verification and Validation (V&V) schemes are introduced by each author; (1) US CFD guidelines; (2) COST/ES1006; (3) German VDI (Verein Deutscher Ingenieure) guidelines; (4) Atomic Energy Society of Japan; (5) Japan Society of Atmospheric Environment; (6) Architectural Institute of Japan. All guidelines were summarized in the same format table shown in the main chapters in order to compare them with each other. In addition to the summary of guidelines, the overview of V&V schemes and many guidelines of CFD modeling in the USA are explained
Breaking up the band: European regulatory cooperation in a post-Brexit world
Since 1995, the European Medicines Agency (EMA) has progressed from harmonising regulation for human and veterinary medicines across the European Union Member State national competent authorities, to galvanising one of the most successful cooperative initiatives for regulation globally. Although the EMA is the focal point for stakeholders, regulation is delivered through the European medicines regulatory network, in which national authorities, like the UK’s Medicines & Healthcare products Regulatory Agency (MHRA), contribute. As with any collaboration, contributions by individual members vary, and the MHRA has been noted as an innovative and highly productive member of the network. Progress in regulation not only in Europe – but also around the world through convergence – can be attributed to this unique European cooperation. The decision by the UK to leave the European Union threatens to mark the end of this cooperation; we argue here that the best decision is to maintain regulatory cooperation under new structures
Six-wave mixing: secular resonances in a higher-order mechanism for second-harmonic generation
Identification de l'acétate de 3-mercaptohexanol, composé à forte odeur de buis, intervenant dans l'arôme des vins de Sauvignon
L'extraction sélective des thiols volatils présents dans un vin a l'état de traces, associée à l'analyse par couplage chromatographie en phase gazeuse (CPG)-détecteur à photométrie de flamme (DPF) et CPG-spectrométrie de masse (SM) de l'extrait obtenu, a permis d'identifier un nouveau constituant de l'arome des vins de Sauvignon, l'acétate de 3-mercaptohexanol, jusqu'ici seulement caractérise dans le fruit de la passion. Le seuil de perception dans l'eau et en solution modèle de ce composé fortement odorant évoquant le buis avec des nuances plus fruitées de pamplemousse et de fruit de la passion est de l'ordre de quelques ng/1. L'acétate de 3-mercaptohexanol pourrait contribuer significativement à l'arôme variétal des vins de Sauvignon.Identification of 3-mercaptohexyl acetate in Sauvignon wine, a powerful aromatic compound exhibiting box-tree odorSelective extraction of volatile mercaptans present in wines at trace levels, combined with capillary gas chromatographic (GC) analysis using flame photometric detector (FPD) revealed the presence of a previously unreported compound in Sauvignon wine. 3-mercaptohexylacetate was identified by comparison of chromatographic and mass spectrum data with those of the reference compound. This mercapto ester, recently found in passion-fruit, exhibits aroma reminiscent of box tree with grapefruit and passion fruit notes. Its perception threshold in water and model solution is around 2-4 ng/l. 3-mercaptohexylacetate may contribute to the typical varietal aroma of Sauvignon wines
Limits on Simultaneous and Delayed Optical Emission from Well-Localized Fast Radio Bursts
We present the largest compilation to date of optical observations during and
following fast radio bursts (FRBs). The data set includes our dedicated
simultaneous and follow-up observations, as well as serendipitous archival
survey observations, for a sample of 15 well-localized FRBs, including 8
repeating and 7 one-off sources. Our simultaneous (and nearly simultaneous with
a -sec delay) optical observations of 7 (1) bursts from the repeating FRB
20220912A provide the deepest such limits to date for any extragalactic FRB,
reaching a luminosity limit of erg s
( erg s); these observations are also the
deepest to date in terms of optical flux to radio fluence ratio of ms ( ms),
and place a limit on the flux ratio of
on a msec timescale or () on a sec
timescale. These simultaneous limits provide useful constraints in the context
of FRB emission models, such as the pulsar magnetosphere and pulsar nebula
models. Interpreting all available optical limits in the context of the FRB
synchrotron maser model, we find that they constrain the flare energies to
erg (depending on the distances of the various
repeating FRBs, with erg for SGR 1935+2154). These limits
are generally at least an order of magnitude larger than the energies inferred
from the FRBs themselves, although in the case of FRB 20220912A our
simultaneous and rapid follow-up observations severely restrict the model
parameter space. We conclude by exploring the potential of future rapid
response and simultaneous observations with large optical telescopes.Comment: 22 pages, 8 figures, submitted to ApJL. Please let us know if we
missed any optical and/or radio observations of the FRB sampl
The Spectral Lag of GRB060505: A Likely Member of the Long Duration Class
Two long gamma-ray bursts, GRB 060505 and GRB 060614, occurred in nearby
galaxies at redshifts of 0.089 and 0.125 respectively. Due to their proximity
and durations, deep follow-up campaigns to search for supernovae (SNe) were
initiated. However none were found in either case, to limits more than two
orders of magnitude fainter than the prototypical GRB-associated SN, 1998bw. It
was suggested that the bursts, in spite of their durations (4 and 102 s),
belonged to the population of short GRBs which has been shown to be unrelated
to SNe. In the case of GRB 060614 this argument was based on a number of
indicators, including the negligible spectral lag, which is consistent with
that of short bursts. GRB 060505 has a shorter duration, but no spectral lag
was measured. We present the spectral lag measurements of GRB 060505 using
Suzakus Wide Area Monitor and the Swift Burst Alert Telescope. We find that the
lag is 0.36+/- 0.05 s, inconsistent with the lags of short bursts and
consistent with the properties of long bursts and SN-GRBs. These results
support the association of GRB 060505 with other low-luminosity GRBs also found
in star-forming galaxies and indicates that at least some massive stars may die
without bright SNe.Comment: Accepted by ApJL, 5 pages, 3 Figure
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