Significant Limb-Brightening in the Inner Parsec of Markarian 501

TL;DR

This paper presents high-resolution VLBA images of Markarian 501, revealing extreme limb-brightening in the inner jet that supports a spine-layer jet structure, with detailed measurements of jet properties and potential superluminal motion.

Contribution

It provides the first detailed observational evidence of limb-brightening in the inner parsec of Markarian 501's jet, supporting the spine-layer jet model.

Findings

Extreme limb-brightening observed in the inner jet

Measured jet opening angle and brightness ratio

Possible superluminal motion in the jet layer

Abstract

We present three 43 GHz images and a single 86 GHz image of Markarian 501 from VLBA observations in 2005. The 86 GHz image shows a partially resolved core with a flux density of about 200 mJy and a size of about 300 Schwarzschild radii, similar to recent results by Giroletti et al. Extreme limb-brightening is found in the inner parsec of the jet in the 43 GHz images, providing strong observational support for a `spine-layer' structure at this distance from the core. The jet is well resolved transverse to its axis, allowing Gaussian model components to be fit to each limb of the jet. The spine-layer brightness ratio and relative sizes, the jet opening angle, and a tentative detection of superluminal motion in the layer are all discussed.