126 research outputs found
A Search for Gamma-Ray Burst Optical Emission with the Automated Patrol Telescope
The Automated Patrol Telescope (APT) is a wide-field (5 X 5 deg.s), modified
Schmidt capable of covering large gamma-ray burst (GRB) localization regions to
produce a high rate of GRB optical emission measurements. Accounting for
factors such as bad weather and incomplete overlap of our field and large GRB
localization regions, we estimate our search will image the actual location of
20-41 BATSE GRB sources each year. Long exposures will be made for these
images, repeated for several nights, to detect delayed optical transients (OTs)
with light curves similar to those already discovered. The APT can also respond
within about 20 sec. to GRB alerts from BATSE to search for prompt emission
from GRBs. We expect to image more than 2.4 GRBs/yr. during gamma-ray emission.
More than 5.1 will be imaged/yr. within about 20 sec. of emission. The APT's 50
cm aperture is much larger than other currently operating experiments used to
search for prompt emission, and the APT is the only GRB dedicated telescope in
the Southern Hemisphere. Given the current rate of about 25% OTs per X/gamma
localization, we expect to produce a sample of about 10 OTs for detailed
follow-up observations in 1-2 years of operation.Comment: 4 pages latex + 3 ps figures. Download a single tar file of ps at
http://panisse.lbl.gov/public/bruce/optgrbsearch.tar.g
First Weak-lensing Results from "See Change": Quantifying Dark Matter in the Two Z>1.5 High-redshift Galaxy Clusters SPT-CL J2040-4451 and IDCS J1426+3508
We present a weak-lensing study of SPT-CLJ2040-4451 and IDCSJ1426+3508 at
z=1.48 and 1.75, respectively. The two clusters were observed in our "See
Change" program, a HST survey of 12 massive high-redshift clusters aimed at
high-z supernova measurements and weak-lensing estimation of accurate cluster
masses. We detect weak but significant galaxy shape distortions using IR images
from the WFC3, which has not yet been used for weak-lensing studies. Both
clusters appear to possess relaxed morphology in projected mass distribution,
and their mass centroids agree nicely with those defined by both the galaxy
luminosity and X-ray emission. Using an NFW profile, for which we assume that
the mass is tightly correlated with the concentration parameter, we determine
the masses of SPT-CL J2040-4451 and IDCS J1426+3508 to be
M_{200}=8.6_{-1.4}^{+1.7}x10^14 M_sun and 2.2_{-0.7}^{+1.1}x10^14 M_sun,
respectively. The weak-lensing mass of SPT-CLJ2040-4451 shows that the cluster
is clearly a rare object. Adopting the central value, the expected abundance of
such a massive cluster at z>1.48 is only ~0.07 in the parent 2500 sq. deg.
survey. However, it is yet premature to claim that the presence of this cluster
creates a serious tension with the current LCDM paradigm unless that tension
will remain in future studies after marginalizing over many sources of
uncertainties such as the accuracy of the mass function and the
mass-concentration relation at the high mass end. The mass of IDCSJ1426+3508 is
in excellent agreement with our previous ACS-based weak-lensing result while
the much higher source density from our WFC3 imaging data makes the current
statistical uncertainty ~40% smaller.Comment: Accepted to Ap
Scientific Computing Meets Big Data Technology: An Astronomy Use Case
Scientific analyses commonly compose multiple single-process programs into a
dataflow. An end-to-end dataflow of single-process programs is known as a
many-task application. Typically, tools from the HPC software stack are used to
parallelize these analyses. In this work, we investigate an alternate approach
that uses Apache Spark -- a modern big data platform -- to parallelize
many-task applications. We present Kira, a flexible and distributed astronomy
image processing toolkit using Apache Spark. We then use the Kira toolkit to
implement a Source Extractor application for astronomy images, called Kira SE.
With Kira SE as the use case, we study the programming flexibility, dataflow
richness, scheduling capacity and performance of Apache Spark running on the
EC2 cloud. By exploiting data locality, Kira SE achieves a 2.5x speedup over an
equivalent C program when analyzing a 1TB dataset using 512 cores on the Amazon
EC2 cloud. Furthermore, we show that by leveraging software originally designed
for big data infrastructure, Kira SE achieves competitive performance to the C
implementation running on the NERSC Edison supercomputer. Our experience with
Kira indicates that emerging Big Data platforms such as Apache Spark are a
performant alternative for many-task scientific applications
Going Forward with the Nancy Grace Roman Space Telescope Transient Survey: Validation of Precision Forward-Modeling Photometry for Undersampled Imaging
The Nancy Grace Roman Space Telescope (Roman) is an observatory for both
wide-field observations and coronagraphy that is scheduled for launch in the
mid 2020's. Part of the planned survey is a deep, cadenced field or fields that
enable cosmological measurements with type Ia supernovae (SNe Ia). With a pixel
scale of 0".11, the Wide Field Instrument will be undersampled, presenting a
difficulty for precisely subtracting the galaxy light underneath the SNe. We
use simulated data to validate the ability of a forward-model code (such codes
are frequently also called "scene-modeling" codes) to perform precision
supernova photometry for the Nancy Grace Roman Space Telescope SN survey. Our
simulation includes over 760,000 image cutouts around SNe Ia or host galaxies
(~ 10% of a full-scale survey). To have a realistic 2D distribution of
underlying galaxy light, we use the VELA simulated high-resolution images of
galaxies. We run each set of cutouts through our forward-modeling code which
automatically measures time-dependent SN fluxes. Given our assumed inputs of a
perfect model of the instrument PSFs and calibration, we find biases at the
millimagnitude level from this method in four red filters (Y106, J129, H158,
and F184), easily meeting the 0.5% Roman inter-filter calibration requirement
for a cutting-edge measurement of cosmological parameters using SNe Ia.
Simulated data in the bluer Z087 filter shows larger ~ 2--3 millimagnitude
biases, also meeting this requirement, but with more room for improvement. Our
forward-model code has been released on Zenodo.Comment: Accepted for Publication in PAS
Multi-Color Light Curves of Type Ia Supernovae on the Color-Magnitude Diagram: a Novel Step Toward More Precise Distance and Extinction Estimates
We show empirically that fits to the color-magnitude relation of Type Ia
supernovae after optical maximum can provide accurate relative extragalactic
distances. We report the discovery of an empirical color relation for Type Ia
light curves: During much of the first month past maximum, the magnitudes of
Type Ia supernovae defined at a given value of color index have a very small
magnitude dispersion; moreover, during this period the relation between
magnitude and color (or or color) is strikingly linear, to
the accuracy of existing well-measured data. These linear relations can provide
robust distance estimates, in particular, by using the magnitudes when the
supernova reaches a given color. After correction for light curve strech factor
or decline rate, the dispersion of the magnitudes taken at the intercept of the
linear color-magnitude relation are found to be around 0.08 for the
sub-sample of supernovae with \BVm , and around 0.11 for the
sub-sample with \BVm . This small dispersion is consistent with
being mostly due to observational errors. The method presented here and the
conventional light curve fitting methods can be combined to further improve
statistical dispersions of distance estimates. It can be combined with the
magnitude at maximum to deduce dust extinction. The slopes of the
color-magnitude relation may also be used to identify intrinsically different
SN Ia systems. The method provides a tool that is fundamental to using SN Ia to
estimate cosmological parameters such as the Hubble constant and the mass and
dark energy content of the universe.Comment: ApJ, in pres
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