486 research outputs found
A Determination of H_0 with the CLASS Gravitational Lens B1608+656: III. A Significant Improvement in the Precision of the Time Delay Measurements
The gravitational lens CLASS B1608+656 is the only four-image lens system for
which all three independent time delays have been measured. This makes the
system an excellent candidate for a high-quality determination of H_0 at
cosmological distances. However, the original measurements of the time delays
had large (12-20%) uncertainties, due to the low level of variability of the
background source during the monitoring campaign. In this paper, we present
results from two additional VLA monitoring campaigns. In contrast to the ~5%
variations seen during the first season of monitoring, the source flux density
changed by 25-30% in each of the subsequent two seasons. We analyzed the
combined data set from all three seasons of monitoring to improve significantly
the precision of the time delay measurements; the delays are consistent with
those found in the original measurements, but the uncertainties have decreased
by factors of two to three. We combined the delays with revised isothermal mass
models to derive a measurement of H_0. Depending on the positions of the galaxy
centroids, which vary by up to 0.1 arcsec in HST images obtained with different
filters, we obtain H_0 = 61-65 km/s/Mpc, for (Omega_M,Omega_L) = (0.3,0.7). The
value of H_0 decreases by 6% if (Omega_M,Omega_L) = (1.0,0.0). The formal
uncertainties on H_0 due to the time delay measurements are +/- 1 (+/- 2)
km/s/Mpc for the 1-sigma (2-sigma) confidence limits. Thus, the systematic
uncertainties due to the lens model, which are on the order of +/- 15 km/s/Mpc,
now dominate the error budget for this system. In order to improve the
measurement of H_0 with this lens, new models that incorporate the constraints
provided by stellar dynamics and the optical/infrared Einstein ring seen in HST
images must be developed.Comment: Accepted for publication in ApJ. 32 pages, 8 figures (3 in color
Time delay of SBS 0909+532
The time delays between the components of a lensed quasar are basic tools to
analyze the expansion of the Universe and the structure of the main lens galaxy
halo. In this paper, we focus on the variability and time delay of the double
system SBS 0909+532A,B as well as the time behaviour of the field stars. We use
VR optical observations of SBS 0909+532A,B and the field stars in 2003. The
frames were taken at Calar Alto, Maidanak and Wise observatories, and the VR
light curves of the field stars and quasar components are derived from aperture
and point-spread function fitting methods. We measure the R-band time delay of
the system from the chi-square and dispersion techniques and 1000 synthetic
light curves based on the observed records. One nearby field star (SBS
0909+532c) is found to be variable, and the other two nearby field stars are
non-variable sources. With respect to the quasar components, the R-band records
seem more reliable and are more densely populated than the V-band ones. The
observed R-band fluctuations permit a pre-conditioned measurement of the time
delay. From the chi-square minimization, if we assume that the quasar emission
is observed first in B and afterwards in A (in agreement with basic
observations of the system and the corresponding predictions), we obtain a
delay of - 45 (+ 1)/(- 11) days (95% confidence interval). The dispersion
technique leads to a similar delay range. A by-product of the analysis is the
determination of a totally corrected flux ratio in the R band (corrected by the
time delay and the contamination due to the galaxy light). Our 95% measurement
of this ratio (0.575 +/- 0.014 mag) is in excellent agreement with previous
results from contaminated fluxes at the same time of observation.Comment: 26 pages, 15 figures, Astronomy and Astrophysics (see also
http://www.astro.ulg.ac.be/RPub/Colloques/JENAM/proceedings/proceedings.html
- Quasars Section
Further Investigation of the Time Delay, Magnification Ratios, and Variability in the Gravitational Lens 0218+357
High precision VLA flux density measurements for the lensed images of
0218+357 yield a time delay of 10.1(+1.5-1.6)days (95% confidence). This is
consistent with independent measurements carried out at the same epoch (Biggs
et al. 1999), lending confidence in the robustness of the time delay
measurement. However, since both measurements make use of the same features in
the light curves, it is possible that the effects of unmodelled processes, such
as scintillation or microlensing, are biasing both time delay measurements in
the same way. Our time delay estimates result in confidence intervals that are
somewhat larger than those of Biggs et al., probably because we adopt a more
general model of the source variability, allowing for constant and variable
components. When considered in relation to the lens mass model of Biggs et al.,
our best-fit time delay implies a Hubble constant of H_o = 71(+17-23) km/s-Mpc
for Omega_o=1 and lambda_o=0 (95% confidence; filled beam). This confidence
interval for H_o does not reflect systematic error, which may be substantial,
due to uncertainty in the position of the lens galaxy. We also measure the flux
ratio of the variable components of 0218+357, a measurement of a small region
that should more closely represent the true lens magnification ratio. We find
ratios of 3.2(+0.3-0.4) (95% confidence; 8 GHz) and 4.3(+0.5-0.8) (15 GHz).
Unlike the reported flux ratios on scales of 0.1", these ratios are not
strongly significantly different. We investigate the significance of apparent
differences in the variability properties of the two images of the background
active galactic nucleus. We conclude that the differences are not significant,
and that time series much longer than our 100-day time series will be required
to investigate propagation effects in this way.Comment: 33 pages, 9 figures. Accepted for publication in ApJ. Light curve
data may be found at http://space.mit.edu/RADIO/papers.htm
Time delay between images of the lensed quasar UM673
We study brightness variations in the double lensed quasar UM673 (Q0142-100)
with the aim of measuring the time delay between its two images. In the paper
we combine our previously published observational data of UM673 obtained during
the 2003 - 2005 seasons at the Maidanak Observatory with archival and recently
observed Maidanak and CTIO UM673 data. We analyze the V, R and I-band light
curves of the A and B images of UM673, which cover ten observational seasons
from August 2001 to November 2010. We also analyze the time evolution of the
difference in magnitudes between images A and B of UM673 over more than ten
years. We find that the quasar exhibits both short-term (with amplitude of \sim
0.1 mag in the R band) and high-amplitude (\sim 0.3 mag) long-term variability
on timescales of about several months and several years, respectively. These
brightness variations are used to constrain the time delay between the images
of UM673. From cross-correlation analysis of the A and B quasar light curves
and error analysis we measure the mean time delay and its error of 89 \pm11
days. Given the input time delay of 88 days, the most probable value of the
delay that can be recovered from light curves with the same statistical
properties as the observed R-band light curves of UM673 is 95{+5/-16}{+14/-29}
days (68 and 95 % confidence intervals). Analysis of the V - I color variations
and V, R and I-band magnitude differences of the quasar images does not show
clear evidence of the microlensing variations between 1998 and 2010.Comment: Submitted to A&A, 11 pages, 9 figure
QSO size ratios from multiband monitoring of a microlensing high-magnification event
We introduce a new scheme to study the nature of the central engine in a
lensed QSO. The compact emission regions could have different sizes in
different optical wavelengths, and our framework permits to obtain the source
size ratios when a microlensing special high-magnification event (e.g., a
caustic crossing event, a two-dimensional maximum crossing event and so on) is
produced in one of the QSO components. To infer the source size ratios, only
cross-correlations between the brightness records in different optical bands
are required. While the deconvolution method leads to a richer information (1D
intrinsic luminosity profiles), the new approach is free of the technical
problems with complex inversion procedures. Using simulations related to recent
VR data of Q2237+0305A, we discuss the ability of the scheme in the
determination of the visible-to-red ratio q = . We conclude that
extremely accurate fluxes (with a few microJy uncertainties, or equivalently, a
few milli-magnitudes errors) can lead to ~10% measurements of q. Taking into
account the errors in the fluxes of Q2237+0305A from a normal ground-based
telescope, ~10 microJy (~10 mmag), it must be possible the achievement of
smaller errors from the current superb-telescopes, and thus, an accurate
determination of q. Obviously, to measure the visible-to-red ratio, the light
curves cannot be contaminated by an intrinsic event or an important
high-frequency intrinsic signal, i.e., exceeding the microJy (mmag) level. For
an arbitrary lensed QSO, we finally remark that the framework seems to work
better with very fast microlensing events.Comment: 28 pages, 13 figures, accepted for publication in A&
Lack of Mutual Respect in Relationship The Endangered Partner
Violence in a relationship and in a family setting has been
an issue of concern to various interest groups and professional organizations.
Of particular interest in this article is violence against women
in a relationship. While there is an abundance of knowledge on violence
against women in general, intimate or partner femicide seems to have
received less attention. Unfortunately, the incidence of violence against
women, and intimate femicide in particular, has been an issue of concern
in the African setting.
This article examines the trends of intimate femicide in an African setting
in general, and in Botswana in particular. The increase in intimate
femicide is an issue of concern, which calls for collective effort to address.
This article also examines trends offemicide in Botswana, and the
antecedents and the precipitating factors. Some studies have implicated
societal and cultural dynamics as playing significant roles in intimate
femicide in the African setting. It is believed that the patriarchal nature
of most African settings and the ideology of male supremacy have relegated
women to a subordinate role. Consequently, respect for women
in any relationship with men is lopsided in favor of men and has led to
abuse of women, including intimate femicide. Other militating factors in
intimate femicide ,are examined and the implications for counseling to
assist the endangered female partner are discussed
Preferred sunspot longitudes: Non-axisymmetry and differential rotation
As recently found, the distribution of sunspots is non-axisymmetric and spot
group formation implies the existence of two persistent active longitudes
separated by 180 degrees. Here we quantitatively study the non-axisymmetry of
sunspot occurrence. In a dynamic reference frame inferred from the differential
rotation law, the raw sunspot data show a clear clustering around the
persistent active longitudes. The differential rotation describing the dynamic
frame is quantified in terms of the equatorial angular velocity and the
differential rotation rate, which appear to be significantly different from
those for individual sunspots. This implies that the active longitudes are not
linked to the depth of sunspot anchoring. In order to quantify the observed
effect, we introduce a measure of the non-axisymmetry of the sunspot
distribution. The non-axisymmetric component is found to be highly significant,
and the ratio of its strength to that of the axisymmetric one is roughly 1:10.
This provides additional constraints for solar dynamo models.Comment: 7 pages, 8 figures, Astronomy and Astrophysics, in pres
Energy levels in polarization superlattices: a comparison of continuum strain models
A theoretical model for the energy levels in polarization superlattices is
presented. The model includes the effect of strain on the local
polarization-induced electric fields and the subsequent effect on the energy
levels. Two continuum strain models are contrasted. One is the standard strain
model derived from Hooke's law that is typically used to calculate energy
levels in polarization superlattices and quantum wells. The other is a
fully-coupled strain model derived from the thermodynamic equation of state for
piezoelectric materials. The latter is more complete and applicable to strongly
piezoelectric materials where corrections to the standard model are
significant. The underlying theory has been applied to AlGaN/GaN superlattices
and quantum wells. It is found that the fully-coupled strain model yields very
different electric fields from the standard model. The calculated intersubband
transition energies are shifted by approximately 5 -- 19 meV, depending on the
structure. Thus from a device standpoint, the effect of applying the
fully-coupled model produces a very measurable shift in the peak wavelength.
This result has implications for the design of AlGaN/GaN optical switches.Comment: Revtex
Optimization of neuronal morphologies for pattern recognition
© 2010 de Sousa et al; licensee BioMed Central Ltd.Poster presented at CNS 2010Peer reviewe
An optical time-delay estimate for the double gravitational lens system B1600+434
We present optical I-band light curves of the gravitationally lensed double
QSO B1600+434 from observations obtained at the Nordic Optical Telescope (NOT)
between April 1998 and November 1999. The photometry has been performed by
simultaneous deconvolution of all the data frames, involving a numerical lens
galaxy model. Four methods have been applied to determine the time delay
between the two QSO components, giving a mean estimate of \Delta_t = 51+/-4
days (95% confidence level). This is the fourth optical time delay ever
measured. Adopting a Omega=0.3, Lambda=0 Universe and using the mass model of
Maller et al. (2000), this time-delay estimate yields a Hubble parameter of
H_0=52 (+14, -8) km s^-1 Mpc^-1 (95% confidence level) where the errors include
time-delay as well as model uncertainties. There are time-dependent offsets
between the two (appropriately shifted) light curves that indicate the presence
of external variations due to microlensing.Comment: 15 pages, 4 figures, accepted for publication in Ap
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