2025 Project Description

The Deepest View of AGN Jet : Unveiling the Nature of the Blazar Jet Core in 3C 279

Supervisors

Minchul Kam, Keiichi Asada
Find out more about supervisors on ASIAA website

Task Description and Goals

Blazars are a subset of Active Galactic Nuclei (AGN) with highly collimated relativistic jets. Their parsec-scale morphologies are characterized by a bright compact feature found upstream of their extended jet, the so-called VLBI core (hereafter referred to as the core). Despite typically being the brightest region in a jet, the nature of this core is still unclear. The Blandford and Konigl (BK) jet model describes the core as the most upstream of the conical-shaped jet where the optical depth reaches unity. In this scenario, the core position shifts toward the base of the jet at higher frequency; this is known as core-shift effect. On the other hand, observations at higher frequencies also suggest that the core could be a standing recollimation shock. In this case, the core-shift would stop at higher frequencies where the recollimation shock becomes trasparent.

These two models can be tested by measuring the Faraday rotation measure (RM) at the core of blazars at millimeter wavelengths: the core RM is expected to increase with frequency in the former case and to be independent of frequency in the latter case. Our previous studies of a bright blazar 3C 279 using KVN at 22-86 GHz and the optical data suggest that the increase of the RM in centimeter wavelengths does not continue to optical wavelengths but saturates at frequencies of few 100 GHz. This implies that the radio core would be a recollimation shock located upstream of the BK jet that is optically thick at cm wavelengths. To confirm this, the student will analyze the data of 3C 279 obtained with KVN (22-129 GHz), ALMA (90-350 GHz), SMA (230 GHz) in order to fill the frequency gap between the centimeter and optical wavelengths. In addition, the student will reduce and analyze the data from (i) the VLBA at 15-43 GHz and (ii) the GLT+JCMT+KVN as a single VLBI at 86 and 230 GHz in order to confirm if the change of the core sizes as a function of frequency alings with the results from the RM. These analyses of the datasets over unprecedentedly large and dense frequency coverage will enable us, for the first time, to confirm if the RM indeed saturates at mm and sub-mm wavelengths.

Required Background

Understanding about the basics of the Very Long Baseline Interferometry (VLBI) and the Active Galactic Nuclei (AGN) is needed.