4,341 research outputs found
A search for thermal X-ray signatures in Gamma-Ray Bursts II: The Swift sample
In several gamma-ray bursts (GRBs) excess emission, in addition to the
standard synchrotron afterglow spectrum, has been discovered in the early time
X-ray observations. It has been proposed that this excess comes from black body
emission, which may be related to the shock break-out of a supernova in the
GRBs progenitor star. This hypothesis is supported by the discovery of excess
emission in several GRBs with an associated supernova. Using mock spectra we
show that it is only likely to detect such a component, similar to the one
proposed in GRB 101219B, at low redshift and in low absorption environments. We
also perform a systematic search for black body components in all the GRBs
observed with the Swift satellite and find six bursts (GRB 061021, 061110A,
081109, 090814A, 100621A and 110715A) with possible black body components.
Under the assumption that their excess emission is due to a black body
component we present radii, temperatures and luminosities of the emitting
components. We also show that detection of black body components only is
possible in a fraction of the Swift bursts.Comment: 11 pages, 8 figures, accepted for MNRA
Strong spectral evolution during the prompt emission of GRB 070616
Swift has revealed features in GRB early light curves, such as steep decays
and X-ray flares, whose properties are consistent with an internal origin
though they are far from understood. The steep X-ray decay is often explained
using the curvature effect; however a significant number of GRBs display strong
spectral evolution during this phase, and a new mechanism must be invoked to
explain this. Of particular interest are the longest duration GRBs in which the
early emission can be studied in most detail. Here we present data for GRB
070616, in which the prompt emission shows a complex multipeaked structure,
leading to one of the longest prompt emission durations ever recorded. We take
advantage of extensive coverage of such a long burst by all Swift instruments.
Combining data from Swift and Suzaku we study the evolution of the prompt
emission spectrum, following the temporal variability of the peak energy and
spectral slope.Comment: 4 pages, 2 figures (Fig 1 in colour), contributed talk, submitted to
the proceedings of Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9
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The soft X-ray excess AGN RE J2248-511
We model the spectral energy distribution of the ultrasoft broad-line AGN RE
J2248-511 with Comptonised accretion disc models. These are able to reproduce
the steep optical and ultrasoft X-ray slopes, and the derived black hole mass
is consistent with independent mass estimates. This AGN displays properties of
both broad and narrow line Seyfert 1 galaxies, but we conclude that it is
intrinsically a `normal' Seyfert 1 viewed at high inclination angle.Comment: 4 pages, 1 figure. MG10 Proceeding
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A search for thermal X-ray signatures in Gamma-Ray Bursts I: Swift bursts with optical supernovae
The X-ray spectra of Gamma-Ray Bursts can generally be described by an
absorbed power law. The landmark discovery of thermal X-ray emission in
addition to the power law in the unusual GRB 060218, followed by a similar
discovery in GRB 100316D, showed that during the first thousand seconds after
trigger the soft X-ray spectra can be complex. Both the origin and prevalence
of such spectral components still evade understanding, particularly after the
discovery of thermal X-ray emission in the classical GRB 090618. Possibly most
importantly, these three objects are all associated with optical supernovae,
begging the question of whether the thermal X-ray components could be a result
of the GRB-SN connection, possibly in the shock breakout. We therefore
performed a search for blackbody components in the early Swift X-ray spectra of
11 GRBs that have or may have associated optical supernovae, accurately
recovering the thermal components reported in the literature for GRBs 060218,
090618 and 100316D. We present the discovery of a cooling blackbody in GRB
101219B/SN2010ma, and in four further GRB-SNe we find an improvement in the fit
with a blackbody which we deem possible blackbody candidates due to
case-specific caveats. All the possible new blackbody components we report lie
at the high end of the luminosity and radius distribution. GRB 101219B appears
to bridge the gap between the low-luminosity and the classical GRB-SNe with
thermal emission, and following the blackbody evolution we derive an expansion
velocity for this source of order 0.4c. We discuss potential origins for the
thermal X-ray emission in our sample, including a cocoon model which we find
can accommodate the more extreme physical parameters implied by many of our
model fits.Comment: 16 pages, 6 figures, accepted for MNRA
Examining the evidence for dust destruction in GRB 980703
The effects that gamma-ray bursts have on their environments is an important
and outstanding issue. Dust destruction in particular has long been predicted
while observational evidence is difficult to obtain. We examine the evidence
for dust destruction by GRB 980703, in which various inconsistent measurements
of the host galaxy extinction have been made using the GRB afterglow emission.
We construct a spectral energy distribution from nIR to X-ray to measure the
extinction at early times and compare this with previous findings. We also
construct nIR/optical SEDs at intermediate epochs to examine a previously
reported decrease in extinction. The extinction is very high for a GRB host
galaxy. The earliest extinction measurement is likely to be lower than
previously estimated, and consistent with most later measurements. In a series
of SEDs we do not find any evidence of variable extinction. We therefore
conclude that there is no clear evidence of dust destruction in this case.Comment: 6 pages, 4 figures, accepted for publication in A&
Negative regulation ofUltrabithorax expression byengrailed is required for proper specification of wing development in Drosophila melanogaster
In both vertebrates and invertebrates, homeotic selector genes confer morphological differences along the antero-posterior axis. However, insect wing development is independent of all homeotic gene functions, reflecting the ground plan of an ancestral pterygote, which bore wings on all segments. Dipteran insects such asDrosophila are characterized by a pair of wings in the mesothoracic segment. In all other segments, wing development is essentially repressed by different homeotic genes, although in the metathorax they are modified into a pair of halteres. This necessitates that during development all homeotic genes are to be maintained in a repressed state in wing imaginal discs. In this report we show that (i) the function of the segment polarity geneengrailed (en) is critical to keep the homeotic selector geneUltrabithorax (Ubx) repressed in wing imaginal discs, (ii) normal levels of En in the posterior compartment of haltere discs, however, are not enough to completely repressUbx, and (iii) the repression ofUbx byen is independent of Hedgehog signalling through which the long-range signalling ofen is mediated during wing development. Finally we provide evidence for a possible mechanism by whichen repressesUbx. On the basis of these results we propose thaten has acquired two independent functions during the evolution of dorsal appendages. In addition to its well-known function of conferring posterior fate and inducing long-range signalling to pattern the developing appendages, it maintains wing fate by keepingUbx repressed
Teams with lower injury rates have greater success in the Currie Cup rugby union competition
Background: Professional football teams that rank high on the log at the end of the season generally have fewer injuries than teams that rank lower on the log. This highlights the importance of implementing injury prevention measures, not only to protect player welfare and ensure their longevity in the sport, but also to improve the performance of the team. The association between a low incidence of injury and superior performance during a season may be even more relevant in sports with a higher incidence of injury than football, such as rugby union.
Discussion: To examine this association in the South African Currie Cup rugby union competition, time-loss (≥ 1 day training/match play missed) injury data and final position in the competition was examined over five-seasons. Teams who ranked in 1st position had significantly lower average injury rates than teams who ranked in last position [48 injuries per 1 000 player hours (95% C.I 20 to 76) vs 130 injuries per 1 000 player hours (95% C.I 79 to 180)]. More specifically, the team with the lowest injury rate in each season ranked in 1st or 2nd position. This team performance aspect of injury prevention should be highlighted more. In particular, this should be used to assist with communicating the importance of injury prevention programmes to stakeholders directly involved with budgetary allocations in the team. 
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