4 research outputs found
The Allen Telescope Array Twenty-centimeter Survey - A 690-Square-Degree, 12-Epoch Radio Dataset - I: Catalog and Long-Duration Transient Statistics
We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a
multi-epoch (12 visits), 690 square degree radio image and catalog at 1.4GHz.
The survey is designed to detect rare, very bright transients as well as to
verify the capabilities of the ATA to form large mosaics. The combined image
using data from all 12 ATATS epochs has RMS noise sigma = 3.94mJy / beam and
dynamic range 180, with a circular beam of 150 arcsec FWHM. It contains 4408
sources to a limiting sensitivity of S = 20 mJy / beam. We compare the catalog
generated from this 12-epoch combined image to the NRAO VLA Sky Survey (NVSS),
a legacy survey at the same frequency, and find that we can measure source
positions to better than ~20 arcsec. For sources above the ATATS completeness
limit, the median flux density is 97% of the median value for matched NVSS
sources, indicative of an accurate overall flux calibration. We examine the
effects of source confusion due to the effects of differing resolution between
ATATS and NVSS on our ability to compare flux densities. We detect no
transients at flux densities greater than 40 mJy in comparison with NVSS, and
place a 2-sigma upper limit on the transient rate for such sources of 0.004 per
square degree. These results suggest that the > 1 Jy transients reported by
Matsumura et al. (2009) may not be true transients, but rather variable sources
at their flux density threshold.Comment: 41 pages, 19 figures, ApJ accepted; corrected minor typo in Table
LCROSS (Lunar Crater Observation and Sensing Satellite) Observation campaign : strategies, implementation, and lessons learned
NASA's LCROSS (Lunar Crater Observation and Sensing Satellite) mission was designed to explore the nature of previously detected enhanced levels of hydrogen near the lunar poles. The LCROSS mission impacted the spent upper stage of the launch vehicle into a permanently shadowed region of the lunar surface to create an ejecta plume. The resultant impact crater and plume were then observed by the LCROSS Shepherding Spacecraft as well as a cadre of telescopes on the Earth and in space to determine the nature of the materials contained within the permanently shadowed region. The Shepherding Spacecraft then became a second impactor which was also observed by multiple assets. The LCROSS Observation Campaign was a key component of the LCROSS mission. The goal of the Observation Campaign was to realize the scientific benefits of extending the LCROSS observations to multiple ground and space-based assets. This paper describes the LCROSS Observation Campaign and provides an overview of the Campaign coordination and logistics as well as a summary of the observation techniques utilized at a multitude of observatories. Lessons learned from the LCROSS Observation Campaign are also discussed to assist with the planning of future unique observing events.48 page(s