[Paper Review] Systematic effects in apparent proper motion of radio sources

Oleg Titov|ArXiv.org|May 8, 2008

Geophysics and Gravity Measurements10 references3 citations

TL;DR

This paper investigates systematic effects in the apparent proper motion of radio sources, particularly the secular aberration drift caused by the Solar System's galactocentric motion, and examines how relativistic jets in active galactic nuclei can mimic this effect. Using VLBI data and the OCCAM software, the study estimates the secular aberration drift while addressing contamination from intrinsic jet motions that can exceed the drift by factors of 10–100.

ABSTRACT

The galactocentric rotation of the Solar system generates the systematic effect in proper motions known as 'secular aberration drift'. This tiny effect (about five microseconds per year) in the quasar proper motion can be measured by VLBI. However, the motions of relativistic jets from the active extragalactic nuclei can reach several hundred microseconds per year and mimic the proper motion of the observed radio sources. These apparent motions exceed the secular aberration drift by factor of 10-100. In this paper we search the ways to overcome the difficulties and discuss our estimates of the secular aberration drift using OCCAM software.

Motivation & Objective

• To identify and quantify systematic effects distorting apparent proper motions of extragalactic radio sources.
• To isolate the secular aberration drift caused by the Solar System's galactocentric motion from intrinsic source motions.
• To assess the impact of relativistic jet motions, which can mimic or obscure the secular aberration drift.
• To evaluate the feasibility of measuring the secular aberration drift using VLBI techniques and the OCCAM software.
• To provide improved estimates of the secular aberration drift by mitigating contamination from jet-induced apparent motions.

Proposed method

• Utilizes Very Long Baseline Interferometry (VLBI) observations to measure apparent proper motions of radio sources.
• Applies the OCCAM software package to model and analyze the astrometric data with high precision.
• Models the expected secular aberration drift due to the Solar System's motion around the Galactic center.
• Compares observed proper motions with theoretical predictions to detect systematic deviations.
• Analyzes the contribution of relativistic jet motions in active galactic nuclei to apparent source motions.
• Employs statistical and astrometric techniques to separate intrinsic jet motions from the secular aberration drift.

Experimental results

Research questions

• RQ1 To what extent do relativistic jet motions in active galactic nuclei mimic the secular aberration drift in apparent proper motions?
• RQ2 How accurately can the secular aberration drift be measured using current VLBI data and processing software?
• RQ3 What systematic effects in proper motion measurements are introduced by the motion of the Solar System in the Milky Way?
• RQ4 Can the OCCAM software effectively disentangle the secular aberration drift from other apparent motions in radio sources?
• RQ5 What is the magnitude of contamination from jet-induced motions relative to the secular aberration drift?

Key findings

• The secular aberration drift is a small effect, approximately 5 microseconds per year, arising from the Solar System's galactocentric motion.
• Relativistic jet motions in active galactic nuclei can produce apparent proper motions of several hundred microseconds per year, significantly exceeding the secular aberration drift.
• The amplitude of jet-induced apparent motions can be 10 to 100 times larger than the secular aberration drift, posing a major contamination challenge.
• The OCCAM software enables precise estimation of the secular aberration drift by modeling and removing systematic effects from the data.
• The study confirms that careful data processing is essential to isolate the secular aberration drift from intrinsic source motions.
• VLBI remains a viable method for detecting the secular aberration drift, but only with advanced modeling to suppress jet-related systematic errors.