The IPAC Image Subtraction and Discovery Pipeline for the intermediate Palomar Transient Factory

We describe the near real-time transient-source discovery engine for the intermediate Palomar Transient Factory (iPTF), currently in operations at the Infrared Processing and Analysis Center (IPAC), Caltech. We coin this system the IPAC/iPTF Discovery Engine (or IDE). We review the algorithms used for PSF-matching, image subtraction, detection, photometry, and machine-learned (ML) vetting of extracted transient candidates. We also review the performance of our ML classifier. For a limiting signal-to-noise ratio of 4 in relatively unconfused regions, "bogus" candidates from processing artifacts and imperfect image subtractions outnumber real transients by ~ 10:1. This can be considerably higher for image data with inaccurate astrometric and/or PSF-matching solutions. Despite this occasionally high contamination rate, the ML classifier is able to identify real transients with an efficiency (or completeness) of ~ 97% for a maximum tolerable false-positive rate of 1% when classifying raw candidates. All subtraction-image metrics, source features, ML probability-based real-bogus scores, contextual metadata from other surveys, and possible associations with known Solar System objects are stored in a relational database for retrieval by the various science working groups. We review our efforts in mitigating false-positives and our experience in optimizing the overall system in response to the multitude of science projects underway with iPTF.Comment: 66 pages, 21 figures, 7 tables, accepted by PAS

The 1998 November 14 Occultation of GSC 0622-00345 by Saturn. I. Techniques for Ground-Based Stellar Occultations

On 1998 November 14, Saturn and its rings occulted the star GSC 0622-00345. We observed atmospheric immersion with NSFCAM at the National Aeronautics and Space Administration's Infrared Telescope Facility on Mauna Kea, Hawaii. Immersion occurred at 55.5\circ S planetocentric latitude. A 2.3 {\mu}m, methane-band filter suppressed reflected sunlight. Atmospheric emersion and ring data were not successfully obtained. We describe our observation, light-curve production, and timing techniques, including improvements in aperture positioning, removal of telluric scintillation effects, and timing. Many of these techniques are known within the occultation community, but have not been described in the reviewed literature. We present a light curve whose signal-to-noise ratio per scale height is 267, among the best ground-based signals yet achieved, despite a disadvantage of up to 8 mag in the stellar flux compared to prior work.Comment: LaTeX/emulateapj, 6 pages, 3 figures. Online items: The FITS-format light curve and the IDL code for the timing model are available from ApJ or the lead autho

The XMM-Newton serendipitous ultraviolet source survey catalogue

The XMM-Newton Serendipitous Ultraviolet Source Survey (XMM-SUSS) is a catalogue of ultraviolet (UV) sources detected serendipitously by the Optical Monitor (XMM-OM) on-board the XMM-Newton observatory. The catalogue contains ultraviolet-detected sources collected from 2,417 XMM-OM observations in 1-6 broad band UV and optical filters, made between 24 February 2000 and 29 March 2007. The primary contents of the catalogue are source positions, magnitudes and fluxes in 1 to 6 passbands, and these are accompanied by profile diagnostics and variability statistics. The XMM-SUSS is populated by 753,578 UV source detections above a 3 sigma signal-to-noise threshold limit which relate to 624,049 unique objects. Taking account of substantial overlaps between observations, the net sky area covered is 29-54 square degrees, depending on UV filter. The magnitude distributions peak at 20.2, 20.9 and 21.2 in UVW2, UVM2 and UVW1 respectively. More than 10 per cent of sources have been visited more than once using the same filter during XMM-Newton operation, and > 20 per cent of sources are observed more than once per filter during an individual visit. Consequently, the scope for science based on temporal source variability on timescales of hours to years is broad. By comparison with other astrophysical catalogues we test the accuracy of the source measurements and define the nature of the serendipitous UV XMM-OM source sample. The distributions of source colours in the UV and optical filters are shown together with the expected loci of stars and galaxies, and indicate that sources which are detected in multiple UV bands are predominantly star-forming galaxies and stars of type G or earlier.Comment: Accepted for publication in MNRA

Implementation of robust image artifact removal in SWarp through clipped mean stacking

We implement an algorithm for detecting and removing artifacts from astronomical images by means of outlier rejection during stacking. Our method is capable of addressing both small, highly significant artifacts such as cosmic rays and, by applying a filtering technique to generate single frame masks, larger area but lower surface brightness features such as secondary (ghost) images of bright stars. In contrast to the common method of building a median stack, the clipped or outlier-filtered mean stacked point-spread function (PSF) is a linear combination of the single frame PSFs as long as the latter are moderately homogeneous, a property of great importance for weak lensing shape measurement or model fitting photometry. In addition, it has superior noise properties, allowing a significant reduction in exposure time compared to median stacking. We make publicly available a modified version of SWarp that implements clipped mean stacking and software to generate single frame masks from the list of outlier pixels.Comment: PASP accepted; software for download at http://www.usm.uni-muenchen.de/~dgruen