Broad band flux-density monitoring of radio sources with the Onsala twin telescopes
Journal article, 2022

The Onsala twin telescopes (OTT) are two 13 m telescopes located at the Onsala Space Observatory in Sweden. With dual linear polarized broad-band (3-14 GHz) receivers, they are part of the next generation Very Long Baseline Interferometry (VLBI) Global Observing System (VGOS) for geodesy and astrometry. In addition to purely geodetic data products, VGOS will regularly produce full-polarisation images of hundreds of radio sources. These rich monitoring data will be valuable for both astronomy and geodesy. In this pilot study we aimed at monitoring ten bright radio sources to search for flares or similar activity, and at testing the instrument calibration on long (months) and short (hours) time scales. Using the OTT as a standalone instrument, we observed and analysed 91 short (<30 min) sessions spanning seven months. We monitored seven potentially variable radio sources (0059+581, 0552+398, 1144+402, 1156+295, 1617+229, 3C418, OJ287) and three reference calibrators (3C147, 3C286, 3C295). We used the Common Astronomy Software Applications (CASA) package to fringe-fit, bandpass-correct and scale the data to obtain flux densities in the four standard VGOS bands: 3.0-3.5 GHz (band 1), 5.2-5.7 GHz (band 2), 6.3-6.8 GHz (band 3), and 10.2-10.7 GHz (band 4). We obtained simultaneous multi-frequency light curves for ten radio sources. A bright multi-frequency flare is observed in the radio source 0059+581. OJ287 and 1156+295 show significant long-term variability in their light curves. After correcting for instrumental biases, we determine the empirical flux density uncertainty as similar to 5 %.

1144+402

0059+581

Onsala twin telescopes - techniques

Interferometric - galaxies

0552+398

1617+229

3C418

Telescopes

1156+295

Individual

OJ287

Author

Eskil Varenius

Chalmers, Space, Earth and Environment, Geoscience and Remote Sensing

Francesco Maio

University of Pisa

Karine le Bail

Chalmers, Space, Earth and Environment, Geoscience and Remote Sensing

Rüdiger Haas

Chalmers, Space, Earth and Environment, Geoscience and Remote Sensing

Experimental Astronomy

0922-6435 (ISSN) 1572-9508 (eISSN)

Vol. 54 137-155

Subject Categories

Astronomy, Astrophysics and Cosmology

Geophysics

Signal Processing

DOI

10.1007/s10686-022-09867-4

More information

Latest update

10/27/2023