946,660 research outputs found
The bright optical/NIR afterglow of the faint GRB 080710 - Evidence for a jet viewed off axis
We investigate the optical/near-infrared light curve of the afterglow of GRB
080710 in the context of rising afterglows. Optical and near-infrared
photometry was performed using the seven channel imager GROND and the
Tautenburg Schmidt telescope. X-ray data were provided by the X-ray Telescope
onboard the Swift satellite. The optical/NIR light curve of the afterglow of
GRB 080710 is dominated by an initial increase in brightness, which smoothly
turns over into a shallow power law decay. The initially rising achromatic
light curve of the afterglow of GRB 080710 can be accounted for with a model of
a burst viewed off-axis or a single jet in its pre deceleration phase and in an
on-axis geometry. An unified picture of the afterglow light curve and prompt
emission properties can be obtained with an off-axis geometry, suggesting that
late and shallow rising optical light curves of GRB afterglows might be
produced by geometric effects.Comment: 9 pages, 4 figures, accepted by A and
Light curves and spectra from off-axis gamma-ray bursts
If gamma-ray burst prompt emission originates at a typical radius, and if
material producing the emission moves at relativistic speed, then the
variability of the resulting light curve depends on the viewing angle. This is
due to the fact that the pulse evolution time scale is Doppler contracted,
while the pulse separation is not. For off-axis viewing angles , the pulse broadening
significantly smears out the light curve variability. This is largely
independent of geometry and emission processes. To explore a specific case, we
set up a simple model of a single pulse under the assumption that the pulse
rise and decay are dominated by the shell curvature effect. We show that such a
pulse observed off-axis is (i) broader, (ii) softer and (iii) displays a
different hardness-intensity correlation with respect to the same pulse seen
on-axis. For each of these effects, we provide an intuitive physical
explanation. We then show how a synthetic light curve made by a superposition
of pulses changes with increasing viewing angle. We find that a highly variable
light curve, (as seen on-axis) becomes smooth and apparently single-pulsed
(when seen off-axis) because of pulse overlap. To test the relevance of this
fact, we estimate the fraction of off-axis gamma-ray bursts detectable by
\textit{Swift} as a function of redshift, finding that a sizable fraction
(between 10\% and 80\%) of nearby () bursts are observed with
. Based on these
results, we argue that low luminosity gamma-ray bursts are consistent with
being ordinary bursts seen off-axis.Comment: 13 pages, 17 figures, submitted to MNRAS main journal; updated
estimate of the fraction of off-axis grbs seen by Swif
Analytical drafting curves provide exact equations for plotted data
Analytical drafting curves provide explicit mathematical expressions for any numerical data that appears in the form of graphical plots. The curves each have a reference coordinate axis system indicated on the curve as well as the mathematical equation from which the curve was generated
Illumination uniformity in endoscopic imaging
Standardised endoscopic digital images were taken and analysed using an image analysis software (National Instruments Vision Assistant version 7.1.1). The luminance plane was extracted and the pixel intensity distribution was determined along a horizontal line at the position of highest average intensity (centroid). The data was exported to MS Excel and the pixel intensity (y-axis) was plotted against pixel position (x-axis). A trendline using a 2nd order polynomial curve was fitted to each data set. The resultant equation for each curve was compared with equations obtained from other images taken under various illumination conditions and settings
The Impact of the Convective Blueshift Effect on Spectroscopic Planetary Transits
We present here a small anomalous radial velocity (RV) signal expected to be
present in RV curves measured during planetary transits. This signal is induced
by the convective blueshift (CB) effect --- a net blueshift emanating from the
stellar surface, resulting from a larger contribution of rising hot and bright
gas relative to the colder and darker sinking gas. Since the CB radial
component varies across the stellar surface, the light blocked by the planet
during a transit will have a varying RV component, resulting in a small shift
of the measured RVs. The CB-induced anomalous RV curve is different than, and
independent of, the well known Rossiter-McLaughlin (RM) effect, where the
latter is used for determining the sky-projected angle between the host star
rotation axis and the planet's orbital angular momentum axis. The observed RV
curve is the sum of the CB and RM signals, and they are both superposed on the
orbital Keplerian curve. If not accounted for, the presence of the CB RV signal
in the spectroscopic transit RV curve may bias the estimate of the spin-orbit
angle. In addition, future very high precision RVs will allow the use of
transiting planets to study the CB of their host stars.Comment: v2: replaced with accepted versio
A Garside-theoretic approach to the reducibility problem in braid groups
Let denote the -punctured disk in the complex plane, where the
punctures are on the real axis. An -braid is said to be
\emph{reducible} if there exists an essential curve system \C in ,
called a \emph{reduction system} of , such that \alpha*\C=\C where
\alpha*\C denotes the action of the braid on the curve system \C.
A curve system \C in is said to be \emph{standard} if each of its
components is isotopic to a round circle centered at the real axis.
In this paper, we study the characteristics of the braids sending a curve
system to a standard curve system, and then the characteristics of the
conjugacy classes of reducible braids. For an essential curve system \C in
, we define the \emph{standardizer} of \C as \St(\C)=\{P\in
B_n^+:P*\C{is standard}\} and show that \St(\C) is a sublattice of .
In particular, there exists a unique minimal element in \St(\C). Exploiting
the minimal elements of standardizers together with canonical reduction systems
of reducible braids, we define the outermost component of reducible braids, and
then show that, for the reducible braids whose outermost component is simpler
than the whole braid (including split braids), each element of its ultra summit
set has a standard reduction system. This implies that, for such braids,
finding a reduction system is as easy as finding a single element of the ultra
summit set.Comment: 38 pages, 18 figures, published versio
Negative values of the Riemann zeta function on the critical line
We investigate the intersections of the curve with the real axis. We show unconditionally that the
zeta-function takes arbitrarily large positive and negative values on the
critical line.Comment: 18 pages, improved Corollary
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