Localizing the $\gamma$ rays from blazar PKS 1502+106

TL;DR

This study combines VLBI and single dish data to localize gamma-ray emission in the blazar PKS 1502+106, finding it originates 1-16 parsecs from the jet base, beyond the broad-line region.

Contribution

It provides the first detailed localization of gamma-ray emission in PKS 1502+106 using combined VLBI and timing analysis, revealing its position relative to the jet and broad-line region.

Findings

Gamma-ray emission region is 1-16 parsecs from the jet base.

Critical aspect angle towards the source is 2.6 degrees.

The gamma-ray emission occurs beyond the broad-line region.

Abstract

Blazars are among the most variable objects in the universe. They feature energetic jets of plasma that launch from the cores of these active galactic nuclei (AGN), triggering activity from radio up to gamma-ray energies. Spatial localization of the region of their MeV/GeV emission is a key question in understanding the blazar phenomenon. The flat spectrum radio quasar (FSRQ) PKS 1502+106 has exhibited extreme and correlated, radio and high-energy activity that triggered intense monitoring by the Fermi-GST AGN Multi-frequency Monitoring Alliance (F-GAMMA) program and the Global Millimeter VLBI Array (GMVA) down to $\lambda$3 mm (or 86 GHz), enabling the sharpest view to date towards this extreme object. Here, we report on preliminary results of our study of the gamma-ray loud blazar PKS 1502+106, combining VLBI and single dish data. We deduce the critical aspect angle towards the source to be $\theta_{\rm c} = 2.6^{\circ}$, calculate the apparent and intrinsic opening angles and constrain the distance of the 86 GHz core from the base of the conical jet, directly from mm-VLBI but also through a single dish relative timing analysis. Finally, we conclude that gamma rays from PKS 1502+106 originate from a region between ~1-16 pc away from the base of the hypothesized conical jet, well beyond the bulk of broad-line region (BLR) material of the source.