Locating the γ-ray emitting region in the quasar 4C +01.28




Rösch F., Kadler M., Ros E., Gurwell M., Hovatta T., Kreter M., MacDonald N.R., Readhead A.C.S.

Francisco Colomer, Denise Gabuzda, Kazi Rygl, Tiziana Venturi

European VLBI Network Mini-Symposium and Users' Meeting

PublisherSissa Medialab Srl

2022

POS Proceedings of Science

European VLBI Network Mini-Symposium and Users' Meeting 2021 (EVN2021)

Proceedings of Science

POS Proceedings of Science

399

1824-8039

DOIhttps://doi.org/10.22323/1.399.0001

https://pos.sissa.it/399/001

https://research.utu.fi/converis/portal/detail/Publication/175644142



Determining the location of γ-ray emission in blazar jets is a challenging task. Pinpointing the exact location of γ-ray production within a relativistic jet can place strong constraints on our understanding of high-energy astrophysics and astroparticle physics. We present a study of the radio- and γ-bright flat-spectrum radio quasar (FSRQ) 4C +01.28 (PKS B1055+018) in which we try to pinpoint the emission site of several prominent GeV flares. This source shows prominent high-amplitude broadband variability on time scales ranging from days to years. We combine high-resolution VLBI observations provided by the Boston University (BU) Blazar Monitoring Program and multi-band radio light curves over a period of around nine years. We can associate two bright and compact newly ejected jet components with bright flares observed by the Fermi/LAT γ-ray telescope and at various radio frequencies. A cross-correlation analysis reveals the radio light curves systematically lag behind the γ-rays. In combination with the jet kinematics as measured by the VLBA, we use these cross-correlations to constrain a model in which the flares become observable at a given frequency when a plasma component passes through the region at which the bulk energy dissipation takes place at that frequency. We derive a lower limit of the distance of the γ-ray emitting region in 4C +01.28 of several parsecs from the jet base, well beyond the expected extent of the broad-line region. This observational limit challenges blazar-emission models that rely on the broad-line region as a source of seed photons for inverse-Compton scattering.


Last updated on 2024-26-11 at 10:42