14097319
The Stability of the Point Spread Function of the Advanced Camera for Surveys on the Hubble Space Telescope and Implications for Weak Gravitational Lensing
(abridged) We examine the spatial and temporal stability of the HST ACS Wide Field Camera (WFC) point spread function (PSF) using the two square degree COSMOS survey. We show that stochastic aliasing of the PSF necessarily occurs during `drizzling'. This aliasing is maximal if the output pixel scale is equal to the input pixel scale of 0.05''. We show that this source of PSF variation can be significantly reduced by choosing a Gaussian drizzle kernel and by setting the output pixel size to 0.03''. We show that the PSF is temporally unstable, most likely due to thermal fluctuations in the telescope's focus. We find that the primary manifestation of this thermal drift in COSMOS images is an overall slow periodic focus change. Using a modified version of TinyTim, we create undistorted stars in a 30x30 grid across the ACS WFC CCDs. These PSF models are created for telescope focus values in the range -10 microns to +5 microns, thus spanning the allowed range of telescope focus values. We then use the approximately ten well measured stars in each COSMOS field to pick the best-fit focus value for each field. The TinyTim model stars are then used to perform PSF corrections for weak lensing allowing systematics due to incorrectly modeled PSFs to be greatly reduced. We have made the software for PSF modeling using our modified version of TinyTim available to the astronomical community. We show the effects of Charge Transfer Efficiency (CTE) degradation, which distorts the object in the readout direction, mimicking a weak lensing signal. We derive a parametric correction for the effect of CTE on the shapes of objects in the COSMOS field as a function of observation date, position within the ACS WFC field, and object flux.
36960262
Weak Lensing from Space. III. Cosmological Parameters
Weak gravitational lensing provides a unique method to directly map the dark matter in the universe and measure cosmological parameters. Current weak-lensing surveys are limited by the atmospheric seeing from the ground and by the small fields of view of existing space telescopes. We study how a future wide-field space telescope can measure the lensing power spectrum and skewness and thus set constraints on cosmological parameters. The lensing sensitivity was calculated using detailed image simulations and instrumental specifications studied in earlier papers in this series. For instance, the planned SuperNova/Acceleration Probe (SNAP) mission will be able to measure the matter density parameter Ωm and the dark energy equation-of-state parameter w with precisions comparable and nearly orthogonal to those derived with SNAP from supernovae. The constraints degrade by a factor of about 2 if redshift tomography is not used but are little affected if only the skewness is dropped. We also study how the constraints on these parameters depend on the survey geometry and define an optimal observing strategy.
18354661
Weak Lensing from Space. II. Dark Matter Mapping
We study the accuracy with which weak-lensing measurements could be made from a future space-based survey, predicting the subsequent precision of three-dimensional dark matter maps, projected two-dimensional dark matter maps, and mass-selected cluster catalogs. As a baseline, we use the instrumental specifications of the SuperNova/Acceleration Probe (SNAP) satellite. We first compute its sensitivity to weak lensing shear as a function of survey depth. Our predictions are based on detailed image simulations created using "shapelets," a complete and orthogonal parameterization of galaxy morphologies. We incorporate a realistic redshift distribution of source galaxies and calculate the average precision of photometric redshift recovery using the SNAP filter set to be Δz = 0.034. The high density of background galaxies resolved in a wide space-based survey allows projected dark matter maps with an rms sensitivity of 3% shear in 1 arcmin2 cells. This will be further improved using a proposed deep space-based survey, which will be able to detect isolated clusters using a three-dimensional lensing inversion technique with a 1 σ mass sensitivity of approximately 1013 M⊙ at z = 0.25. Weak-lensing measurements from space will thus be able to capture non-Gaussian features arising from gravitational instability and map out dark matter in the universe with unprecedented resolution.
17561360
Search for Invisible Or Lepton-Flavor-Violating Upsilon Decays in BaBar
Both invisible and lepton-flavor-violating Upsilon decays are unobservably rare in the Standard Model, but are each predicted to occur in several beyond-Standard-Model scenarios. We search for invisible, as well as for lepton-flavor-violating, Upsilon decays in a sample of 117 × 10 6
126050065
Indication of Electron Neutrino Appearance in an Accelerator-Produced Muon Neutrino Beam
Indication of Electron Neutrino Appearance in an Accelerator-Produced Muon Neutrino Beam
119385567
FADC signal reconstruction for the MAGIC telescope
Until April 2007 the Major Atmospheric Gamma ray Imaging Cherenkov (MAGIC) telescope used a 300 MSamples/s flash analog-to-digital converter (FADC) system to sample the shaped photomultiplier tube (PMT) signals produced by the captured Cherenkov photons of air showers. Different algorithms to reconstruct the signal from the read-out samples (extractors) have been implemented and are described and compared. Criteria based on the obtained charge and time resolution/bias are defined and used to judge the different extractors, by applying them to calibration, cosmic and pedestal signals. The achievable charge and time resolution have been derived as functions of the number of incident photoelectrons. (C) 2008 Elsevier B.V. All rights reserved.