4,684 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
Precision frequency measurements with interferometric weak values
We demonstrate an experiment which utilizes a Sagnac interferometer to
measure a change in optical frequency of 129 kHz per root Hz with only 2 mW of
continuous wave, single mode input power. We describe the measurement of a weak
value and show how even higher frequency sensitivities may be obtained over a
bandwidth of several nanometers. This technique has many possible applications,
such as precision relative frequency measurements and laser locking without the
use of atomic lines.Comment: 4 pages, 3 figures, published in PR
Ultrasensitive Beam Deflection Measurement via Interferometric Weak Value Amplification
We report on the use of an interferometric weak value technique to amplify
very small transverse deflections of an optical beam. By entangling the beam's
transverse degrees of freedom with the which-path states of a Sagnac
interferometer, it is possible to realize an optical amplifier for polarization
independent deflections. The theory for the interferometric weak value
amplification method is presented along with the experimental results, which
are in good agreement. Of particular interest, we measured the angular
deflection of a mirror down to 560 femtoradians and the linear travel of a
piezo actuator down to 20 femtometers
Optimizing the Signal to Noise Ratio of a Beam Deflection Measurement with Interferometric Weak Values
The amplification obtained using weak values is quantified through a detailed
investigation of the signal to noise ratio for an optical beam deflection
measurement. We show that for a given deflection, input power and beam radius,
the use of interferometric weak values allows one to obtain the optimum signal
to noise ratio using a coherent beam. This method has the advantage of reduced
technical noise and allows for the use of detectors with a low saturation
intensity. We report on an experiment which improves the signal to noise ratio
for a beam deflection measurement by a factor of 54 when compared to a
measurement using the same beam size and a quantum limited detector
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&
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