English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We report multifrequency phase-referenced observations of the nearby radiogalaxy NGC 4261, which has prominent two-sided jets, using the Very LongBaseline Array at 1.4-43 GHz. We measured radio core positions showingobserving frequency dependences (known as "core shift") in both approachingjets and counter jets. The limit of the core position as the frequencyapproaches infinity, which suggests a jet base, is separated by 82$\pm$16${\mu}$as upstream in projection, corresponding to (310$\pm$60)Rs (Rs:Schwarzschild radius) as a deprojected distance, from the 43 GHz core in theapproaching jet. In addition, the innermost component at the counter jet sideappeared to approach the same position at infinity of the frequency, indicatingthat cores on both sides are approaching the same position, suggesting aspatial coincidence with the central engine. Applying a phase referencingtechnique, we also obtained spectral index maps, which indicate that emissionfrom the counter jet is affected by free-free absorption (FFA). The result ofthe core shift profile on the counter jet also requires FFA because the corepositions at 5-15GHz cannot be explained by a simple core shift model based onsynchrotron self-absorption (SSA). Our result is apparently consistent with theSSA core shift with an additional disk-like absorber over the counterjet side.Core shift and opacity profiles at the counter jet side suggest a two-componentaccretion: a radiatively inefficient accretion flow at the inner region and atruncated thin disk in the outer region. We proposed a possible solution aboutdensity and temperature profiles in the outer disk on the basis of the radioobservation.

Determination of Central Engine Position and Accretion Disk Structure in NGC 4261 by Core Shift Measurements