Apertif imaging surveys
The APERture Tile In Focus (Apertif) phased-array feed (PAF) system has been installed at the Westerbork Synthesis Radio Telescope (WSRT) and operates at 1400 MHz. Using the PAFs in the focus of 12 of the WSRT dishes, 40 partially overlapping primary beams are formed on the sky simultaneously, thus having a much larger field of view. The total area covered in one observation by such a mosaic is about 3.5° x 3°, reaching a spatial resolution of about 12’’ x 12’’/sinδ . Apertif has been used as a survey instrument: the Apertif Imaging Surveys have started on July 1, 2019 and have covered about 2500 square degrees of the northern sky. Two surveys have been carried out: the Apertif Wide-area Extragalactic Survey (AWES) and the Apertif Medium-deep Extragalactic Survey (AMES). In addition to the imaging survey, a time-domain survey has also been carried out. A summary of the goals and results of this can be found at http://alert.eu.
The overview paper describing the system and the science goals can be found here: van Cappellen et al. 2022
The processing of the data is done using an automatic pipeline, Apercal. You can find the description here: Adebahr et al. 2021. The pipeline produces radio continuum images, HI and polarisation images and cubes.
First data release
The data and data products from the first data release (covering the first year of observations) are available here.
ASTRON VO server: https://vo.astron.nl/
HIPS map available https://hips.astron.nl/ASTRON/P/apertif_dr1/
Science so far from the imaging surveys:
The discovery with Apertif of a source (J1402+5347) showing extreme (~50%) and rapid variations on a timescale of just 6.5 minutes in the decimetre band (1.4 GHz).
Extreme intra-hour variability of the radio source J1402+5347 discovered with Apertif
More of these - up to now - rare sources have been observed in the Apertif observed areas.
The data cubes produced have allowed a serendipitous detection of the two main OH maser lines at 1667 and 1665 MHz associated with IRAS 10597+5926 at z⊙ = 0.19612
Apertif view of the OH megamaser IRAS 10597+5926: OH 18 cm satellite lines in wide-area H I surveys
Because of their resolution, observing frequency, and sensitivity, the Apertif surveys are providing an ideal complement to the surveys done with LOFAR. Examples of this synergy are presented in these papers:
Combining LOFAR and Apertif Data for Understanding the Life Cycle of Radio Galaxies
The best of both worlds: Combining LOFAR and Apertif to derive resolved radio spectral index images
First release of Apertif imaging survey data, Adams et al.
Characterising the Apertif primary beam response Denes et al.
Continuum source catalog for the first APERTIF data release, Kutkin et al.