[Paper Review] Multifrequency VLBA Monitoring of 3C 273 during the INTEGRAL Campaign in 2003 - I. Kinematics of the Parsec Scale Jet from 43 GHz Data

T. Savolainen, K. Wiik+2 more|CERN Bulletin|Sep 21, 2005

Astrophysics and Cosmic Phenomena27 references38 citations

TL;DR

This study uses 43 GHz VLBA observations to analyze the kinematics of 3C 273's parsec-scale jet during the 2003 INTEGRAL campaign, revealing a velocity gradient with faster components near the southern jet edge. It determines a Doppler factor of δ(C2) = 5.5 ± 1.9 for a newly ejected component, yielding Lorentz factors of 8–18 and indicating intrinsic speed differences beyond viewing angle effects.

ABSTRACT

In this first of a series of papers describing polarimetric multifrequency Very Long Baseline Array (VLBA) monitoring of 3C 273 during a simultaneous campaign with the INTEGRAL gamma-ray satellite in 2003, we present 5 Stokes I images and source models at 7 mm. We show that a part of the inner jet (1-2 milliarcseconds from the core) is resolved in a direction transverse to the flow, and we analyse the kinematics of the jet within the first 10 mas. Based on the VLBA data and simultaneous single-dish flux density monitoring, we determine an accurate value for the Doppler factor of the parsec scale jet, and using this value with observed proper motions, we calculate the Lorentz factors and the viewing angles for the emission components in the jet. Our data indicates a significant velocity gradient across the jet with the components travelling near the southern edge being faster than the components with more northern path. We discuss our observations in the light of jet precession model and growing plasma instabilities.

Motivation & Objective

• To analyze the kinematics of the parsec-scale jet in 3C 273 using high-resolution 43 GHz VLBA data during the 2003 INTEGRAL campaign.
• To determine accurate Doppler factors for jet components using simultaneous flux density variability and light travel time arguments.
• To investigate the origin of observed velocity gradients and non-radial motions in the jet, distinguishing between viewing angle effects and intrinsic dynamics.
• To establish a foundation for multiwavelength modeling by providing a reliable kinematic template for subsequent spectral and polarimetric analysis.
• To assess the compatibility of observed component motions with precessing jet models and fluid dynamical interpretations.

Proposed method

• Obtained five 43 GHz total intensity VLBA images of 3C 273 over a nine-month period in 2003.
• Fitted each image with a model of Gaussian components to track jet component positions and flux densities over time.
• Employed the Difwrap program to estimate robust positional uncertainties for component parameters.
• Used flux density variability and light travel time delays to estimate Doppler factors for prominent components.
• Calculated Lorentz factors and viewing angles from Doppler factors and observed apparent velocities.
• Compared observed component motions with predictions from the precessing jet model of Abraham & Romero (1999), applying uv-data tapering to match resolution.

Experimental results

Research questions

• RQ1 What is the kinematic behavior of the inner parsec-scale jet in 3C 273, particularly near the core (≤2 mas)?
• RQ2 Are the observed velocity gradients across the jet due to differing viewing angles or intrinsic differences in component speeds?
• RQ3 Can the Doppler factor for newly ejected components be reliably estimated using flux variability and light travel time arguments?
• RQ4 How do the observed component motions compare with predictions from the precessing jet model of Abraham & Romero (1999)?
• RQ5 What is the significance of non-radial and curved trajectories in the jet’s component motion for fluid dynamical interpretations?

Key findings

• The jet is resolved transverse to the flow at 1–2 mas from the core, revealing a broadened structure with multiple components.
• A clear velocity gradient is observed, with components near the southern edge moving faster (4.6–13.0 h⁻¹c) than those in the north, indicating intrinsic speed differences.
• The Doppler factor for the newly ejected component C2 is determined as δ(C2) = 5.5 ± 1.9, providing a reliable basis for SSC modeling.
• Lorentz factors range from 8 to 18, confirming that the velocity gradient is not solely due to projection effects from different viewing angles.
• Non-radial and curved motions are observed, suggesting non-ballistic trajectories with large radii of curvature, consistent with fluid dynamical models.
• After uv-data tapering to match the resolution of the Abraham & Romero model, moderate agreement is found, indicating average jet direction may precess, but individual components show faster, more random variations.