2025/10/01 by F. Rösch, M. Kadler, Rösch, F. +13
Physics and Astronomy · #Atomic and Subatomic Physics Research #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Nuclear Physics and Applications #Radiation Detection and Scintillator Technologies
paper · pdf · doi:10.48550/arxiv.2510.01476
openalex publication_date 2025/10/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29
The FSRQ 4C+01.28 is a bright and highly variable radio and γ-ray emitter. We aim to pinpoint the location of the γ-ray emitting region within its jet in order to derive strong constraints on γ-ray emission models for blazar jets. We use radio and γ-ray data obtained with ALMA, OVRO, SMA and Fermi/LAT to study the cross-correlation between γ-ray and multi-frequency radio light curves. Moreover, we employ VLBA observations at 43 GHz over a period of around nine years to study the parsec-scale jet kinematics. To pinpoint the location of the γ-ray emitting region, we use a model in which outbursts shown in the γ-ray and radio light curves are produced when moving jet components pass through the γ-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 γ-ray and radio light curves. The kinematic analysis of the VLBA observations leads to a maximum apparent jet speed of βapp=19±10 and an upper limit on the viewing angle of ϕ < 4 deg. We determine the power law indices that are characterizing the jet geometry, brightness temperature distribution, and core shift to be l=0.974±0.098, s=-3.31±0.31, and kr=1.09±0.17, which are in agreement with a conical jet in equipartition. A cross-correlation analysis shows that the radio light curves follow the γ-ray light curve. We pinpoint the location of the γ-ray emitting region with respect to the jet base to the range of 2.6 pc≤ dγ≤20 pc. Our derived observational limits places the location of γ-ray production in 4C+01.28 beyond the expected extent of the broad-line region (BLR) and therefore challenges blazar-emission models that rely on inverse Compton up-scattering of seed photons from the BLR.