1,057 research outputs found
A Corpus-Based, Pilot Study of Lexical Stress Variation in American English
Phonological free variation describes the phenomenon of there being more than one pronunciation for a word without any change in meaning (e.g. because, schedule, vehicle). The term also applies to words that exhibit different stress patterns (e.g. academic, resources, comparable) with no change in meaning or grammatical category. A corpus-based analysis of free variation is a useful tool for testing the validity of surveys of speakers' pronunciation preferences for certain variants. The current paper presents the results of a corpus-based pilot study of American English, in an attempt to replicate Mompéan's 2009 study of British English
Photospheric Emission in the Joint GBM and Konus Prompt Spectra of GRB 120323A
GRB 120323A is a very intense short Gamma Ray Burst (GRB) detected
simultaneously during its prompt gamma-ray emission phase with the Gamma-ray
Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope and the Konus
experiment on board the Wind satellite. GBM and Konus operate in the keV--MeV
regime, however, the GBM range is broader both toward the low and the high
parts of the gamma-ray spectrum. Analysis of such bright events provide a
unique opportunity to check the consistency of the data analysis as well as
cross-calibrate the two instruments. We performed time-integrated and coarse
time-resolved spectral analysis of GRB 120323A prompt emission. We conclude
that the analyses of GBM and Konus data are only consistent when using a
double-hump spectral shape for both data sets; in contrast, the single-hump of
the empirical Band function, traditionally used to fit GRB prompt emission
spectra, leads to significant discrepancies between GBM and Konus analysis
results. Our two-hump model is a combination of a thermal-like and a
non-thermal component. We interpret the first component as a natural
manifestation of the jet photospheric emission.Comment: 7 pages of article (3 figures and 1 table) + 3 pages of Appendix (3
figures). Submitted to ApJ on 2017 March 2
Do Fermi-LAT observations really imply very large Lorentz factors in GRB outflows ?
Recent detections of GeV photons in a few GRBs by Fermi-LAT have led to
strong constraints on the bulk Lorentz factor in GRB outflows. To avoid a large
gamma gamma optical depth, minimum values of the Lorentz factor are estimated
to be as high as 800-1200 in some bursts. Here we present a detailed
calculation of the gamma gamma optical depth taking into account both the
geometry and the dynamics of the jet. In the framework of the internal shock
model, we compute lightcurves in different energy bands and the corresponding
spectrum and we show how the limits on the Lorentz factor can be significantly
lowered compared to previous estimates.Comment: 4 pages, 3 figures, proceedings of the Gamma Ray Bursts 2010
Conference, Annapolis, USA. Editors: McEnery, Racusin, Gehrel
Swift and Fermi observations of X-ray flares: the case of Late Internal Shock
Simultaneous Swift and Fermi observations of gamma-ray bursts (GRBs) offer a
unique broadband view of their afterglow emission, spanning more than ten
decades in energy. We present the sample of X-ray flares observed by both Swift
and Fermi during the first three years of Fermi operations. While bright in the
X-ray band, X-ray flares are often undetected at lower (optical), and higher
(MeV to GeV) energies. We show that this disfavors synchrotron self-Compton
processes as origin of the observed X-ray emission. We compare the broadband
properties of X-ray flares with the standard late internal shock model, and
find that, in this scenario, X-ray flares can be produced by a late-time
relativistic (Gamma>50) outflow at radii R~10^13-10^14 cm. This conclusion
holds only if the variability timescale is significantly shorter than the
observed flare duration, and implies that X-ray flares can directly probe the
activity of the GRB central engine.Comment: 13 pages, 4 figures, accepted for publication in Ap
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