16,062 research outputs found
Application of the Contouring Method to Extended Microlensed Sources
The method devised by Lewis et al. (1993) for calculating the light curve of
a microlensed point source is expanded to two dimensions to enable the
calculation of light curves of extended sources. This method is significantly
faster than the ray shooting method that has been used in the past. The
increased efficiency is used to obtain much higher resolution light curves over
increased timescales. We investigate the signatures arising from different
source geometries in a realistic microlensing model. We show that a large
fraction of high magnification events (HMEs) in image A of Q2237+0305 involve
only one caustic, and could therefore yield information on the structure of the
quasar continuum through the recognition of a characteristic event shape. In
addition, the cataloguing of HMEs into morphological type will, in theory,
enable the direction of the transverse motion, as well as the source size to be
obtained from long term monitoring.Comment: 10 pages including 4 figures. Accepted for publication in M.N.R.A.
Describing results of 4000 hours of multi environment model verification test Final report
Investigating categorization and formulation of stress and strength factors for semiconductor diodes to provide improved failure rate prediction from mathematical model
A measurement of the transverse velocity of Q2237+0305
Determination of microlensing parameters in the gravitationally lensed quasar
Q2237+0305 from the statistics of high magnification events will require
monitoring for more than 100 years (Wambsganss, Paczynski & Schneider 1990).
However we show that the effective transverse velocity of the lensing galaxy
can be determined on a more realistic time-scale through consideration of the
distribution of light-curve derivatives. The 10 years of existing monitoring
data for Q2237+0305 are analysed. These data display strong evidence for
microlensing that is not associated with a high magnification event. An upper
limit of v < 500 km/sec is obtained for the galactic transverse velocity which
is smaller than previously assumed values. The analysis suggests that the
observed microlensing variation may be predominantly due to stellar proper
motions. The statistical significance of the results obtained from our method
will be increased by the addition of data points from current and future
monitoring campaigns. However reduced photometric errors will be more valuable
than an increased sampling rate.Comment: 16 pages, including 17 figures. Accepted for publication in M.N.R.A.
Interpretation of the OGLE Q2237+0305 microlensing light-curve
The four bright images of the gravitationally lensed quasar Q2237+0305 are
being monitored from the ground (eg. OGLE collaboration, Apache Point
Observatory) in the hope of observing a high magnification event (HME). Over
the past three seasons (1997-1999) the OGLE collaboration has produced
microlensing light-curves with unprecedented coverage. These demonstrate
smooth, independent (therefore microlensing) variability between the images
(Wozniak et al. 2000a,b; OGLE web page). We have retrospectively compared
probability functions for high-magnification event parameters with several
observed light-curve features. We conclude that the 1999 image C peak was due
to the source having passed outside of a cusp rather than to a caustic
crossing. In addition, we find that the image C light-curve shows evidence for
a caustic crossing between the 1997 and 1998 observing seasons involving the
appearance of new critical images. Our models predict that the next image C
event is most likely to arrive 500 days following the 1999 peak, but with a
large uncertainty (100-2000 days). Finally, given the image A light-curve
derivative at the end of the 1999 observing season, our modelling suggests that
a caustic crossing will occur between the 1999 and 2000 observing seasons,
implying a minimum for the image A light-curve ~1-1.5 magnitudes fainter than
the November 1999 level.Comment: 11 pages, 15 figures. Accepted for publication in M.N.R.A.
Limits on the microlens mass function of Q2237+0305
Gravitational microlensing at cosmological distances is potentially a
powerful tool for probing the mass functions of stars and compact objects in
other galaxies. In the case of multiply-imaged quasars, microlensing data has
been used to determine the average microlens mass. However the measurements
have relied on an assumed transverse velocity for the lensing galaxy. Since the
measured mass scales with the square of the transverse velocity, published mass
limits are quite uncertain. In the case of Q2237+0305 we have properly
constrained this uncertainty. The distribution of light curve derivatives
allows quantitative treatment of the relative rates of microlensing due to
proper motions of microlenses, the orbital stream motion of microlenses and the
bulk galactic transverse velocity. By demanding that the microlensing rate due
to the motions of microlenses is the minimum that should be observed we
determine lower limits for the average mass of stars and compact objects in the
bulge of Q2237+0305. If microlenses are assumed to move in an orbital stream
the lower limit ranges between 0.005 and 0.023 solar masses where the the
systematic dependence is due to the fraction of smooth matter and the size of
photometric error assumed for published monitoring data. However, if the
microlenses are assumed to move according to an isotropic velocity dispersion
then a larger lower limit of 0.019-0.11 solar masses is obtained. A significant
contribution of Jupiter mass compact objects to the mass distribution of the
galactic bulge of Q2237+0305 is therefore unambiguously ruled out.Comment: 10 pages, 5 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Society. New version has improved presentatio
Predicting caustic crossing high magnification events in Q2237+0305
The central regions of the gravitationally lensed quasar Q2237+0305 can be
indirectly resolved on nano-arcsecond scales if viewed spectrophotometricly
during a microlensing high magnification event (HME). Q2237+0305 is currently
being monitored from the ground (eg. OGLE collaboration, Apache Point
Observatory), with the goal, among others, of triggering ground and spacecraft
based target of opportunity (TOO) observations of an HME. In this work we
investigate the rate of change (trigger) in image brightness that signals an
imminent HME and importantly, the separation between the trigger and the event
peak. In addition, we produce colour dependent model light-curves by combining
high-resolution microlensing simulations with a realistic model for a thermal
accretion disc source. We make hypothetical target of opportunity spectroscopic
observations using our determination of the appropriate trigger as a guide. We
find that if the source spectrum varies with source radius, a 3 observation TOO
program should be able to observe a microlensing change in the continuum slope
following a light-curve trigger with a success rate of >80%.Comment: 17 pages, 16 figures, accepted for publication in M.N.R.A.
Development of novel multiplex microsatellite polymerase chain reactions to enable high-throughput population genetic studies of Schistosoma haematobium
© 2015 Webster et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. The attached file is the published version of the article
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