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Data release from the first year of the Apertif imaging surveys

The Apertif imaging team has released science data from the first year of science operations of WSRT-Apertif as the Apertif Data Release 1 (DR1). Now the entire astronomical community can access the data collected by Apertif in its first year of observing, which started on 1 July 2019.

Published by the editorial team, 11 November 2020

The Apertif instrument provides forty instantaneous beams, creating a wide field of view, over a wide instantaneous bandwidth, which make WSRT-Apertif an excellent survey instrument. Next to a time-domain survey, aimed at detecting fast radio bursts (FRBs), Apertif is undertaking a two-tiered imaging survey: a wide-area survey and a medium-deep survey. The original four year survey plan calls for the wide-area survey to survey 3000 square degrees of the northern sky between +25d and +60d Declination, with each pointing observed for 1 × 11.5 hours. The medium-deep survey is intended to cover a smaller area of sky, ~300 square degrees, while observing each field for 10 × 11.5 hours to reach a higher sensitivity. 

During the first year of survey operations, the medium-deep survey focused on the Perseus-Pisces region, with an additional medium-deep field in the HETDEX region. The wide tier of the survey focused on the HETDEX region (for overlap with the LoTSS DR1), with additional coverage in the Herschel-ATLAS North Galactic Cap, and in the fall sky between 22h and 0h Right Ascension.

During this period, 219 imaging observations were successful; 65 of these observations build repeated coverage of nine medium-deep fields. There are observations of 160 unique fields; with an effective field-of-view (based on spacing between fields) of 6.44 square degrees, the released observations cover just over 1000 square degrees of sky.

Of these 219 observations, 191 have processed data products available.  These include: multi-frequency synthesis continuum images; Stokes V multi-frequency synthesis images and Stokes Q&U cubes; and dirty spectral line cubes over four frequency ranges, with their associated dirty beam cubes. While all raw observational data are released, processed data are released on the basis of individual beams with the requirement that the continuum image passes validation; not all beams of an observation may be released. A total of 3374 beams pass validation and have released processed data products.

The background image above shows the sky coverage of the Apertif DR1; the orange areas indicate regions of the sky with released data products. The inset image on the left is shows the continuum emission from an interesting radio galaxy, highlighting the sensitivity and resolution of the Apertif continuum images. The inset image on the right shows the extent of the neutral hydrogen (HI) emission (contours) relative to the optical galaxy (background image), demonstrating the power of blind surveys for identifying galaxies with intriguing HI properties.

Information about the data release, including an overview of the observations, (released) data products, the processing pipeline, primary beam images, validation of data products, and data access is provided in the documentation pages:

The Apertif surveys will continue to be supported during 2021.

The data are available via the ASTRON VO pages: A description of how to access these data can be found in the documentation linked above. Need help? Do not hesitate to contact the ASTRON Helpdesk system.

To help us improve the data access services we appreciate your feedback, which can be provided at




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