Apercal -- The Apertif Calibration Pipeline

Abstract

Apertif (APERture Tile In Focus) is one of the Square Kilometre Array (SKA) pathfinder facilities. The Apertif project is an upgrade to the 50-year-old Westerbork Synthesis Radio Telescope (WSRT) using phased-array feed technology. The new receivers create 40 individual beams on the sky, achieving an instantaneous sky coverage of 6.5 square degrees. The primary goal of the Apertif Imaging Survey is to perform a wide survey of 3500 square degrees (AWES) and a medium deep survey of 350 square degrees (AMES) of neutral atomic hydrogen (up to a redshift of 0.26), radio continuum emission and polarisation. Each survey pointing yields 4.6 TB of correlated data. The goal of Apercal is to process this data and fully automatically generate science ready data products for the astronomical community while keeping up with the survey observations. We make use of common astronomical software packages in combination with Python based routines and parallelisation. We use an object oriented module-based approach to ensure easy adaptation of the pipeline. A Jupyter notebook based framework allows user interaction and execution of individual modules as well as a full automatic processing of a complete survey observation. If nothing interrupts processing, we are able to reduce a single pointing survey observation on our five node cluster with 24 physical cores and 256 GB of memory each within 24h keeping up with the speed of the surveys. The quality of the generated images is sufficient for scientific usage for 44 % of the recorded data products with single images reaching dynamic ranges of several thousands. Future improvements will increase this percentage to over 80 %. Our design allowed development of the pipeline in parallel to the commissioning of the Apertif system.

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Cited by in corpus (11)

• The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics
• First release of Apertif imaging survey data
• Continuum source catalog for the first APERTIF data release
• The Apertif science verification campaign - Characteristics of polarised radio sources
• Seeing the forest and the trees: a radio investigation of the ULIRG Mrk 273
• An interference detection strategy for Apertif based on AOFlagger 3
• Apertif 1.4 GHz continuum observations of the Boötes field and their combined view with LOFAR
• Survey-scale discovery-based research processes: Evaluating a bespoke visualisation environment for astronomical survey data
• Gas-rich dwarf galaxy multiples in the Apertif HI survey
• Apertif, Phased Array Feeds for the Westerbork Synthesis Radio Telescope
• Spectral indices in active galactic nuclei as seen by Apertif and LOFAR