1,029 research outputs found
SiPMs for cryogenic temperature
The DarkSide-20k collaboration is preparing to equip 20 m^2 of SiPMs working
in liquid argon at 86 K for the direct search of WIMPs. The collaboration had
to solve many technological aspects, such as the development of SiPM optimized
for operation in liquid argon, the readout of large SiPM-based detectors, the
reliable packaging of more than 200000 SiPMs using radiopure materials. The
packaging solutions available for cryogenic applications and the performances
of the newest cryogenic extended gain SiPMs from FBK will be discussed
MERLIN/VLA imaging of the gravitational lens system B0218+357
Gravitational lenses offer the possibility of accurately determining the
Hubble parameter (H_0) over cosmological distances, and B0218+357 is one of the
most promising systems for an application of this technique. In particular this
system has an accurately measured time delay (10.5+/-0.4 d; Biggs et al. 1999)
and preliminary mass modelling has given a value for H_0 of 69 +13/-19
km/s/Mpc. The error on this estimate is now dominated by the uncertainty in the
mass modelling. As this system contains an Einstein ring it should be possible
to constrain the model better by imaging the ring at high resolution. To
achieve this we have combined data from MERLIN and the VLA at a frequency of 5
GHz. In particular MERLIN has been used in multi-frequency mode in order to
improve substantially the aperture coverage of the combined data set. The
resulting map is the best that has been made of the ring and contains many new
and interesting features. Efforts are currently underway to exploit the new
data for lensing constraints using the LensClean algorithm (Kochanek & Narayan
1992).Comment: Accepted for publication in MNRAS. 6 pages, 4 included PostScript
figure
High resolution observations and mass modelling of the CLASS gravitational lens B1152+199
We present a series of high resolution radio and optical observations of the
CLASS gravitational lens system B1152+199 obtained with the Multi-Element
Radio-Linked Interferometer Network (MERLIN), Very Long Baseline Array (VLBA)
and Hubble Space Telescope (HST). Based on the milliarcsecond-scale
substructure of the lensed radio components and precise optical astrometry for
the lensing galaxy, we construct models for the system and place constraints on
the galaxy mass profile. For a single galaxy model with surface mass density
Sigma(r) propto r^-beta, we find that 0.95 < beta < 1.21 at 2-sigma confidence.
Including a second deflector to represent a possible satellite galaxy of the
primary lens leads to slightly steeper mass profiles.Comment: 7 pages, post-referee revision for MNRA
The Spatial Structure of An Accretion Disk
Based on the microlensing variability of the two-image gravitational lens
HE1104-1805 observed between 0.4 and 8 microns, we have measured the size and
wavelength-dependent structure of the quasar accretion disk. Modeled as a power
law in temperature, T proportional to R^-beta, we measure a B-band (0.13
microns in the rest frame) half-light radius of R_{1/2,B} = 6.7 (+6.2 -3.2) x
10^15 cm (68% CL) and a logarithmic slope of beta=0.61 (+0.21 -0.17) for our
standard model with a logarithmic prior on the disk size. Both the scale and
the slope are consistent with simple thin disk models where beta=3/4 and
R_{1/2,B} = 5.9 x 10^15 cm for a Shakura-Sunyaev disk radiating at the
Eddington limit with 10% efficiency. The observed fluxes favor a slightly
shallower slope, beta=0.55 (+0.03 -0.02), and a significantly smaller size for
beta=3/4.Comment: 5 pages, 4 figures, submitted to Ap
SiPMs for cryogenic temperature
The DarkSide-20k collaboration is preparing to equip 20 m2 of SiPMs working in liquid argon at 86 K for the direct search of WIMPs. The collaboration had to solve many technological aspects, such as the development of SiPM optimized for operation in liquid argon, the readout of large SiPM-based detectors, the reliable packaging of more than 200000 SiPMs using radiopure materials. The packaging solutions available for cryogenic applications and the performances of the newest cryogenic extended gain SiPMs from FBK will be discussed
Effects of Ellipticity and Shear on Gravitational Lens Statistics
We study the effects of ellipticity in lens galaxies and external tidal shear
from neighboring objects on the statistics of strong gravitational lenses. For
isothermal lens galaxies normalized so that the Einstein radius is independent
of ellipticity and shear, ellipticity {\it reduces} the lensing cross section
slightly, and shear leaves it unchanged. Ellipticity and shear can
significantly enhance the magnification bias, but only if the luminosity
function of background sources is steep. Realistic distributions of ellipticity
and shear {\it lower} the total optical depth by a few percent for most source
luminosity functions, and increase the optical depth only for steep luminosity
functions. The boost in the optical depth is noticeable (>5%) only for surveys
limited to the brightest quasars (L/L_* > 10). Ellipticity and shear broaden
the distribution of lens image separations but do not affect the mean.
Ellipticity and shear naturally increase the abundance of quadruple lenses
relative to double lenses, especially for steep source luminosity functions,
but the effect is not enough (by itself) to explain the observed
quadruple-to-double ratio. With such small changes to the optical depth and
image separation distribution, ellipticity and shear have a small effect on
cosmological constraints from lens statistics: neglecting the two leads to
biases of just Delta Omega_M = 0.00 \pm 0.01 and Delta Omega_Lambda = -0.02 \pm
0.01 (where the errorbars represent statistical uncertainties in our
calculations).Comment: Optical depth normalization discussed. Matches the published versio
The Importance of Lens Galaxy Environments
While many strong gravitational lens galaxies are suspected to lie in groups
or clusters of galaxies, environmental effects in lens models are often
unconstrained and sometimes ignored. We show that this creates significant
biases in a variety of lensing applications, by creating mock lenses associated
with each of 13 galaxies in a realistic model group, and then analyzing them
with standard techniques. We find that standard models of double lenses, which
neglect environment, grossly overestimate the ellipticity of the lens galaxy
(de/e~0.5) and the Hubble constant (dh/h~0.22). Standard models of quad lenses,
which approximate the environment as a tidal shear, recover the ellipticity
reasonably well (|de/e|<~0.24) but overestimate the Hubble constant
(dh/h~0.15), and have significant (~30%) errors in the millilensing analyses
used to constrain the amount of substructure in dark matter halos. For both
doubles and quads, standard models slightly overestimate the velocity
dispersion of the lens galaxy (d(sigma)/sigma~0.06), and underestimate the
magnifications of the images (d(mu)/mu ~ -0.25). Standard analyses of lens
statistics overestimate Omega_Lambda (by 0.05-0.14), and underestimate the
ratio of quads to doubles (by a factor of 2). These biases help explain some
long-standing puzzles (such as the high observed quad/double ratio), but
aggravate others (such as the low value of H_0 inferred from lensing). Most of
the biases are caused by neglect of the convergence from the mass associated
with the environment, but additional uncertainty is introduced by neglect of
higher-order terms. Fortunately, we show that directly observing and modeling
lens environments should make it possible to remove the biases and reduce the
uncertainties associated with environments to the few percent level. (Abridged)Comment: 14 emulateapj pages; accepted in Ap
Gravitational Lensing by Power-Law Mass Distributions: A Fast and Exact Series Approach
We present an analytical formulation of gravitational lensing using familiar
triaxial power-law mass distributions, where the 3-dimensional mass density is
given by . The deflection angle and magnification factor are
obtained analytically as Fourier series. We give the exact expressions for the
deflection angle and magnification factor. The formulae for the deflection
angle and magnification factor given in this paper will be useful for numerical
studies of observed lens systems. An application of our results to the Einstein
Cross can be found in Chae, Turnshek, & Khersonsky (1998). Our series approach
can be viewed as a user-friendly and efficient method to calculate lensing
properties that is better than the more conventional approaches, e.g.,
numerical integrations, multipole expansions.Comment: 24 pages, 3 Postscript figures, ApJ in press (October 10th
The Rewards of Patience: An 822 Day Time Delay in the Gravitational Lens SDSS J1004+4112
We present 107 new epochs of optical monitoring data for the four brightest
images of the gravitational lens SDSS J1004+4112 observed between October 2006
and June 2007. Combining this data with the previously obtained light curves,
we determine the time delays between images A, B and C. We confirm our previous
measurement finding that A leads B by dt_BA=40.6+-1.8 days, and find that image
C leads image A by dt_CA=821.6+-2.1 days. The lower limit on the remaining
delay is that image D lags image A by dt_AD>1250 days. Based on the
microlensing of images A and B we estimate that the accretion disk size at a
rest wavelength of 2300 angstrom is 10^{14.8+-0.3} cm for a disk inclination of
cos{i}=1/2, which is consistent with the microlensing disk size-black hole mass
correlation function given our estimate of the black hole mass from the MgII
line width of logM_BH/M_sun=8.44+-0.14. The long delays allow us to fill in the
seasonal gaps and assemble a continuous, densely sampled light curve spanning
5.7 years whose variability implies a structure function with a logarithmic
slope of gamma = 0.35+-0.02. As C is the leading image, sharp features in the C
light curve can be intensively studied 2.3 years later in the A/B pair,
potentially allowing detailed reverberation mapping studies of a quasar at
minimal cost.Comment: Submitted to ApJ, 12 pages, 3 figure
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