Gamma-ray emitting region location in 4C +01.28

We aim to pinpoint the location of the gamma-ray emitting region within its jet in order to derive strong constraints on gamma-ray emission models for blazar jets. We use radio and gamma-ray monitoring data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), the Owens Valley Radio Observatory (OVRO), the Submillimeter Array (SMA) and the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (Fermi/LAT) to study the cross-correlation between gamma-ray and multi-frequency radio light curves.

Moreover, we employ Very Long Baseline Array (VLBA) observations at 43GHz over a period of around nine years to study the parsec-scale jet kinematics of 4C +01.28. To pinpoint the location of the gamma-ray emitting region, we use a model in which outbursts shown in the gamma-ray and radio light curves are produced when moving jet components pass through the gamma-ray emitting and the radio core regions. We find two bright and compact newly ejected jet components that are likely associated with a high activity period visible in the Fermi/LAT gamma-ray and different radio light curves.