Astrophysical Journal Letters
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.
Piner, B. G., Pant, N., Edwards, P. G., & Wiik, K. (2008). Significant Limb-Brightening in the Inner Parsec of Markarian 501. Astrophysical Journal Letters 690(1). 10.1088/0004-637X/690/1/L31