Radio continuum emission from knots in the DG Tau jet

TL;DR

This study detects and models radio knots in the DG Tau jet, showing their correlation with optical knots and proposing a shock-based variability model, while noting the enigmatic nature of X-ray knots.

Contribution

First detection of radio knots in DG Tau's jet and a model explaining their emission through shock features with intrinsic variability.

Findings

Radio knots coincide with optical knots within error margins.

A shock model with variable ejection velocities explains radio flux densities.

Four successive knots ejected every 4.80 years travel at 198 km/s.

Abstract

Context: HH 158, the jet from the young star DG Tau, is one of the few sources of its type where jet knots have been detected at optical and X-ray wavelengths. Aims: To search, using Very Large Array observations of this source, radio knots and if detected, compare them with the optical and X-ray knots. To model the emission from the radio knots. Methods: We analyzed archive data and also obtained new Very Large Array observations of this source, as well as an optical image, to measure the present position of the knots. We also modeled the radio emission from the knots in terms of shocks in a jet with intrinsically time-dependent ejection velocities. Results: We detected radio knots in the 1996.98 and 2009.62 VLA data. These radio knots are,within error, coincident with optical knots. We also modeled satisfactorily the observed radio flux densities as shock features from a jet with intrinsic variability. All the observed radio, optical, and X-ray knot positions can be intepreted as four successive knots, ejected with a period of 4.80 years and traveling away from the source with a velocity of 198 km s$^{-1}$ in the plane of the sky. Conclusions: The radio and optical knots are spatially correlated and our model can explain the observed radio flux densities. However, the X-ray knots do not appear to have optical or radio counterparts and their nature remains poorly understood.