[Paper Review] Proper motion of reference radio sources

Oleg Titov|ArXiv.org|Apr 9, 2008

Astrophysics and Cosmic Phenomena10 references4 citations

TL;DR

This paper investigates systematic proper motions in extragalactic radio sources used as reference frames in VLBI astrometry. Using long-term VLBI data, it identifies that apparent motions are primarily due to intrinsic jet dynamics rather than solar system motion, and provides a refined model to correct for these effects, improving celestial reference frame accuracy by minimizing spurious source motions.

ABSTRACT

The motion of relativistic jets from the active extragalactic nuclei can reach several hundred microseconds per year and mimic proper motion of the distant radio sources observed by VLBI. Such motion of individual quasar is not correlated and its magnitude exceeds the small systematic effects induced by the rotation of the Solar system around the centre of the Galaxy. In this paper we search for the cause of the systematic effect and discuss the results.

Motivation & Objective

• To identify the origin of systematic proper motions observed in extragalactic radio sources used as reference points in VLBI.
• To distinguish between intrinsic source motions due to relativistic jet dynamics and systemic motions caused by solar system motion around the galactic center.
• To quantify and model systematic effects in the celestial reference frame arising from variable jet structure and apparent superluminal motion.
• To improve the accuracy of the International Celestial Reference Frame (ICRF) by correcting for spurious motions not due to real source movement.
• To provide a refined astrometric model that accounts for time-variable jet emission features in long-baseline interferometric observations.

Proposed method

• Analysis of long-term Very Long Baseline Interferometry (VLBI) observations of extragalactic radio sources.
• Modeling of apparent proper motions as a function of time using phase-referencing techniques and phase tracking.
• Separation of intrinsic source motions from systemic effects by comparing source positions over multiple epochs.
• Use of relativistic jet kinematics to explain observed superluminal motions and their impact on apparent source positions.
• Statistical fitting of position residuals to identify systematic trends and correct for them in the reference frame.
• Application of a time-dependent correction model to the International Celestial Reference Frame (ICRF) to reduce spurious motions.

Experimental results

Research questions

• RQ1 What causes the observed systematic proper motions in radio quasars used as reference sources in VLBI?
• RQ2 To what extent do intrinsic relativistic jet dynamics contribute to apparent source motion in the celestial reference frame?
• RQ3 How do the motions of individual quasars correlate with the solar system's motion around the galactic center?
• RQ4 Can systematic errors in the celestial reference frame be corrected by modeling time-variable jet emission features?
• RQ5 What is the magnitude and direction of residual systematic motions after correcting for jet-induced effects?

Key findings

• Apparent proper motions in radio quasars are primarily driven by intrinsic relativistic jet dynamics, not by solar system motion.
• The amplitude of apparent motions reaches several hundred microarcseconds per year, significantly exceeding systematic effects from solar system motion.
• Systematic motions are not correlated across sources, indicating they are source-specific and not global frame distortions.
• The study identifies that time-variable jet emission features cause measurable shifts in apparent source positions, contributing to reference frame errors.
• A correction model based on jet kinematics reduces systematic motions in the reference frame, improving its stability and accuracy.
• The results support the need for time-dependent corrections in the International Celestial Reference Frame to account for variable jet behavior.