Broad band flux-density monitoring of radio sources with the Onsala twin telescopes

Context and aims: The Onsala twin telescopes (OTT) are two 13 m located at the Space Observatory in Sweden. With dual linear polarized broad-band (3-14 GHz) receivers, they part of next generation Very Long Baseline Interferometry (VLBI) Global Observing System (VGOS) for geodesy astrometry. In addition to purely geodetic data products, VGOS will regularly produce full-polarisation images hundreds radio sources. These rich monitoring be valuable both astronomy geodesy. this pilot study we aim monitor 10 bright sources search flares or similar activity, verify instrument calibration on long (months) short (hours) time scales. Method: We observed analysed 91 (<30 min) sessions spanning 7 months. monitored seven potentially variable (0059+581, 0552+398, 1144+402, 1156+295, 1617+229, 3C418, OJ287) three reference calibrators (3C147, 3C286, 3C295). used Common Astronomy Software Applications (CASA) package fringe-fit, bandpass-correct scale obtain flux densities four standard bands: 3.0-3.5 GHz (band 1), 5.2-5.7 2), 6.3-6.8 3), 10.2-10.7 4). Results: simultaneous multi-frequency light curves ten A flare is source 0059+581. OJ287 1156+295 show significant long-term variability. Conclusions: After correcting instrumental biases, determine empirical density uncertainty as $\sim$5%. Future refined analysis methods allow regular more fainter