Removing systematic effects from astronomical images taken with CCDs requires a detailed understanding of the physics of the imaging process. To aid in this understanding, we have built detailed electrostatic simulations of the LSST CCDs. In order to
build an electrostatic model of the LSST CCDs, physical information about the CCDs is required. These details include things such as the physical dimensions of the components of the CCD, dopant profiles, and in some cases, electrical measurements of the CCD. This work documents the results of these physical and electrical measurements on LSST CCDs.
The Brighter-Fatter (hereafter BF) effect in CCD sensors causes increases in the image size of bright objects due to electrostatic repulsion of collected charges. Correcting this effect in the LSST camera is required in order to meet the science goal
s of the project, especially galaxy shape measurements for weak lensing. The current plan for BF image correction in the LSST is to use the deconvolution method described in Coulton, et.al. [1]. In this work, we study the linearity of the BF effect and effectiveness of the Coulton correction, using both simulation tools and measurements made on prototype LSST CCDs from both CCD vendors. We conclude that the proposed image correction method may be adequate to meet the LSST science goals, although more work is needed on the algorithms used to generate the image correction kernel from sensor measurements.
We employ electrostatic conversion drift calculations to match CCD pixel signal covariances observed in flat field exposures acquired using candidate sensor devices for the LSST Camera. We thus constrain pixel geometry distortions present at the end
of integration, based on signal images recorded. We use available data from several operational voltage parameter settings to validate our understanding. Our primary goal is to optimize flux point-spread function (FPSF) estimation quantitatively, and thereby minimize sensor-induced errors which may limit performance in precision astronomy applications. We consider alternative compensation scenarios that will take maximum advantage of our understanding of this underlying mechanism in data processing pipelines currently under development. To quantitatively capture the pixel response in high-contrast/high dynamic range operational extrema, we propose herein some straightforward laboratory tests that involve altering the time order of source illumination on sensors, within individual test exposures. Hence the word {it hysteretic} in the title of this paper.
In this work, we report on a detailed simulation of the Bullet Cluster (1E0657-56) merger, including magnetohydrodynamics, plasma cooling, and adaptive mesh refinement. We constrain the simulation with data from gravitational lensing reconstructions
and 0.5 - 2 keV Chandra X-ray flux map, then compare the resulting model to higher energy X-ray fluxes, the extracted plasma temperature map, Sunyaev-Zeldovich effect measurements, and cluster halo radio emission. We constrain the initial conditions by minimizing the chi-squared figure of merit between the full 2D observational data sets and the simulation, rather than comparing only a few features such as the location of subcluster centroids, as in previous studies. A simple initial configuration of two triaxial clusters with NFW dark matter profiles and physically reasonable plasma profiles gives a good fit to the current observational morphology and X-ray emissions of the merging clusters. There is no need for unconventional physics or extreme infall velocities. The study gives insight into the astrophysical processes at play during a galaxy cluster merger, and constrains the strength and coherence length of the magnetic fields. The techniques developed here to create realistic, stable, triaxial clusters, and to utilize the totality of the 2D image data, will be applicable to future simulation studies of other merging clusters. This approach of constrained simulation, when applied to well-measured systems, should be a powerful complement to present tools for understanding X-ray clusters and their magnetic fields, and the processes governing their formation.
