66 research outputs found
The Mass-Richness Relation of MaxBCG Clusters from Quasar Lensing Magnification using Variability
Accurate measurement of galaxy cluster masses is an essential component not
only in studies of cluster physics, but also for probes of cosmology. However,
different mass measurement techniques frequently yield discrepant results. The
SDSS MaxBCG catalog's mass-richness relation has previously been constrained
using weak lensing shear, Sunyaev-Zeldovich (SZ), and X-ray measurements. The
mass normalization of the clusters as measured by weak lensing shear is >~25%
higher than that measured using SZ and X-ray methods, a difference much larger
than the stated measurement errors in the analyses. We constrain the
mass-richness relation of the MaxBCG galaxy cluster catalog by measuring the
gravitational lensing magnification of type I quasars in the background of the
clusters. The magnification is determined using the quasars' variability and
the correlation between quasars' variability amplitude and intrinsic
luminosity. The mass-richness relation determined through magnification is in
agreement with that measured using shear, confirming that the lensing strength
of the clusters implies a high mass normalization, and that the discrepancy
with other methods is not due to a shear-related systematic measurement error.
We study the dependence of the measured mass normalization on the cluster halo
orientation. As expected, line-of-sight clusters yield a higher normalization;
however, this minority of haloes does not significantly bias the average
mass-richness relation of the catalog.Comment: 9 pages. Accepted for publication in Ap
The QUEST Data Processing Software Pipeline
A program that we call the QUEST Data Processing Software Pipeline has been
written to process the large volumes of data produced by the QUEST camera on
the Samuel Oschin Schmidt Telescope at the Palomar Observatory. The program
carries out both aperture and PSF photometry, combines data from different
repeated observations of the same portion of sky, and produces a Master Object
Catalog. A rough calibration of the data is carried out. This program, as well
as the calibration procedures and quality checks on the output are described.Comment: 17 pages, 1 table, 8 figure
Blazar Optical Variability in the Palomar-QUEST Survey
We study the ensemble optical variability of 276 FSRQs and 86 BL Lacs in the
Palomar-QUEST Survey with the goal of searching for common fluctuation
properties, examining the range of behavior across the sample, and
characterizing the appearance of blazars in such a survey so that future work
can more easily identify such objects. The survey, which covers 15,000 square
degrees multiple times over 3.5 years, allows for the first ensemble blazar
study of this scale. Variability amplitude distributions are shown for the FSRQ
and BL Lac samples for numerous time lags, and also studied through structure
function analyses. Individual blazars show a wide range of variability
amplitudes, timescales, and duty cycles. Of the best sampled objects, 35% are
seen to vary by more than 0.4 magnitudes; for these, the fraction of
measurements contributing to the high amplitude variability ranges constantly
from about 5% to 80%. Blazar variability has some similarities to that of type
I quasars but includes larger amplitude fluctuations on all timescales. FSRQ
variability amplitudes are particularly similar to those of QSOs on timescales
of several months, suggesting significant contributions from the accretion disk
to the variable flux at these timescales. Optical variability amplitudes are
correlated with the maximum apparent velocities of the radio jet for the subset
of FSRQs with MOJAVE VLBA measurements, implying that the optically variable
flux's strength is typically related to that of the radio emission. We also
study CRATES radio-selected FSRQ candidates, which show similar variability
characteristics to known FSRQs; this suggests a high purity for the CRATES
sample.Comment: 29 pages, 12 figures. Accepted for publication in Ap
Highly Variable Objects in the Palomar-QUEST Survey: A Blazar Search using Optical Variability
We identify 3,113 highly variable objects in 7,200 square degrees of the
Palomar-QUEST Survey, which each varied by more than 0.4 magnitudes
simultaneously in two broadband optical filters on timescales from hours to
roughly 3.5 years. The primary goal of the selection is to find blazars by
their well-known violent optical variability. Because most known blazars have
been found in radio and/or X-ray wavelengths, a sample discovered through
optical variability may have very different selection effects, elucidating the
range of behavior possible in these systems. A set of blazars selected in this
unusual manner will improve our understanding of the physics behind this
extremely variable and diverse class of AGN. The object positions, variability
statistics, and color information are available using the Palomar-QUEST CasJobs
server. The time domain is just beginning to be explored over large sky areas;
we do not know exactly what a violently variable sample will hold. About 20% of
the sample has been classified in the literature; over 70% of those objects are
known or likely AGN. The remainder largely consists of a variety of variable
stars, including a number of RR Lyrae and cataclysmic variables.Comment: 22 pages (preprint format), 2 figures. Accepted for publication in
ApJ. References update
Measuring Lensing Magnification of Quasars by Large Scale Structure using the Variability-Luminosity Relation
We introduce a technique to measure gravitational lensing magnification using
the variability of type I quasars. Quasars' variability amplitudes and
luminosities are tightly correlated, on average. Magnification due to
gravitational lensing increases the quasars' apparent luminosity, while leaving
the variability amplitude unchanged. Therefore, the mean magnification of an
ensemble of quasars can be measured through the mean shift in the
variability-luminosity relation. As a proof of principle, we use this technique
to measure the magnification of quasars spectroscopically identified in the
Sloan Digital Sky Survey, due to gravitational lensing by galaxy clusters in
the SDSS MaxBCG catalog. The Palomar-QUEST Variability Survey, reduced using
the DeepSky pipeline, provides variability data for the sources. We measure the
average quasar magnification as a function of scaled distance (r/R200) from the
nearest cluster; our measurements are consistent with expectations assuming NFW
cluster profiles, particularly after accounting for the known uncertainty in
the clusters' centers. Variability-based lensing measurements are a valuable
complement to shape-based techniques because their systematic errors are very
different, and also because the variability measurements are amenable to
photometric errors of a few percent and to depths seen in current wide-field
surveys. Given the data volume expected from current and upcoming surveys, this
new technique has the potential to be competitive with weak lensing shear
measurements of large scale structure.Comment: Accepted for publication in Ap
LSQ13ddu: a rapidly evolving stripped-envelope supernova with early circumstellar interaction signatures
This paper describes the rapidly evolving and unusual supernova LSQ13ddu, discovered by the La Silla-QUEST survey. LSQ13ddu displayed a rapid rise of just 4.8 ± 0.9 d to reach a peak brightness of â19.70 ± 0.02 mag in the LSQgr band. Early spectra of LSQ13ddu showed the presence of weak and narrow HeI features arising from interaction with circumstellar material (CSM). These interaction signatures weakened quickly, with broad features consistent with those seen in stripped-envelope SNe becoming dominant around two weeks after maximum. The narrow HeI velocities are consistent with the wind velocities of luminous blue variables but its spectra lack the typically seen hydrogen features. The fast and bright early light curve is inconsistent with radioactive â”â¶Ni powering but can be explained through a combination of CSM interaction and an underlying â”â¶Ni decay component that dominates the later time behaviour of LSQ13ddu. Based on the strength of the underlying broad features, LSQ13ddu appears deficient in He compared to standard SNe Ib
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