The Large Array Survey Telescope-Pipeline. II. Image Subtraction and Transient Detection

Abstract

Context. The Large Array Survey Telescope (LAST) is a wide-field visual-band survey designed to explore the variable and transient sky with high cadence. Its raw data stream is automatically processed in near real time at the observatory site, producing science-quality images, catalogs, and transient alerts. Transient alerts are then reported to the Transient Name Server (TNS). Aims. The LAST pipeline comprises two major components: (i) processing and calibration of single images followed by coaddition of $20\times 20$s exposures, producing single-image and coadded-image catalogs; and (ii) subtraction of coadded images from calibrated reference images followed by transient detection. In this work we present a detailed description and validation of the second component of the pipeline. Methods. Transient detection is based on the algorithm for proper image subtraction (ZOGY). We combine ZOGY subtraction with the Translient statistic for sub-pixel motion discrimination, together with a sequence of deterministic filtering steps, to produce a clean stream of transient candidates without the use of machine learning. Results. Using commissioning data, the pipeline achieves a preliminary $5\sigma$ limiting magnitude of $20.3$-$20.7$mag, a single-epoch transient detection efficiency of $\sim 80$%, and a purity of $\gtrsim 90$% at signal-to-noise ratio of $\ge 7.5\sigma$.

submitted to A&A

References in corpus (29)

• The Gaia mission
• LSST: from Science Drivers to Reference Design and Anticipated Data Products
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• The Palomar Transient Factory: System Overview, Performance and First Results
• The Zwicky Transient Facility: Science Objectives
• Hydrogen-poor superluminous stellar explosions
• Rapidly-Evolving and Luminous Transients from Pan-STARRS1
• A Wolf-Rayet-like progenitor of supernova SN 2013cu from spectral observations of a wind
• A First Catalog of Variable Stars Measured by the Asteroid Terrestrial-impact Last Alert System (ATLAS)
• Proper image subtraction - optimal transient detection, photometry and hypothesis testing
• The Automatic Learning for the Rapid Classification of Events (ALeRCE) Alert Broker
• The Half Million Quasars (HMQ) Catalogue
• An Early Warning System for Asteroid Impact
• The Palomar Transient Factory photometric calibration
• Machine Learning for the Zwicky Transient Facility
• GLADE+: An Extended Galaxy Catalogue for Multimessenger Searches with Advanced Gravitational-wave Detectors
• The Palomar Transient Factory photometric catalog 1.0
• catsHTM - A tool for fast accessing and cross-matching large astronomical catalogs
• How to coadd images? I. Optimal source detection and photometry using ensembles of images
• The Large Array Survey Telescope -- System Overview and Performances
• How to coadd images? II. A coaddition image that is optimal for any purpose in the background dominated noise limit
• The ZTF Source Classification Project: I. Methods and Infrastructure
• Seeing-limited imaging sky surveys -- small vs. large telescopes
• Minutes-duration Optical Flares with Supernova Luminosities
• A code for robust astrometric solution of astronomical images
• The Large Array Survey Telescope -- Science Goals
• Accurate photometric calibration by fitting the system transmission