TY - JOUR

T1 - Monthly 43 GHz vlba polarimetric monitoring of 3C 120 over 16 epochs

T2 - Evidence for trailing shocks in a relativistic jet

AU - Gómez, José Luis

AU - Marscher, Alan P.

AU - Alberdi, Antonio

AU - Jorstad, Svetlana G.

AU - Agudo, Ivan

N1 - Funding Information: This research was supported in part by Spain’s Dirección General de Investigación Científica y Técnica (DGICYT) grant PB97-1164, by US National Science Foundation (NSF) grant AST 98-02941, and by a Fulbright commission for the collaboration between Spain and the US. The VLBA and VLA are instruments of the National Radio Astronomy Observatory, a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. We are grateful to Barry Clark for scheduling ad hoc VLA time in order to determine the polarization position angle calibration.

PY - 2001

Y1 - 2001

N2 - We present a 16 month sequence of monthly polarimetric 43 GHz VLBA images of the radio galaxy 3C 120. The images probe the inner regions of the radio jet of this relatively nearby superluminal radio galaxy at a linear resolution of 0.07 h-l65 pc (H0 = 65 h65 km s-1 Mpc-1). We follow the motion of a number of features with apparent velocities between 4.01 ± 0.08 and 5.82 ± 0.13 h65-1 c. A new superluminal knot, moving at 4.29 ± 0.16 h65-1 c, is observed to be ejected from the core at a time coincident with the largest flare ever observed for this source at millimeter wavelengths. Changes in the position angle of this component, as well as a progressive rotation of its magnetic polarization vector, suggest the presence of a twisted (resembling a helix in projection) configuration of the underlying jet magnetic field and jet geometry. We identify several knots that appear in the wake of the new superluminal component, moving at proper motions ∼4 times slower than any of the other moving knots observed in 3C 120. These features have properties similar to those of the "trailing" shocks seen in relativistic, time-dependent, hydrodynamical, and emission simulations of compact jets. Such trailing compressions are triggered by pinch-mode jet-body instabilities caused by the propagation of a strong perturbation, which we associate with the new strong superluminal component.

AB - We present a 16 month sequence of monthly polarimetric 43 GHz VLBA images of the radio galaxy 3C 120. The images probe the inner regions of the radio jet of this relatively nearby superluminal radio galaxy at a linear resolution of 0.07 h-l65 pc (H0 = 65 h65 km s-1 Mpc-1). We follow the motion of a number of features with apparent velocities between 4.01 ± 0.08 and 5.82 ± 0.13 h65-1 c. A new superluminal knot, moving at 4.29 ± 0.16 h65-1 c, is observed to be ejected from the core at a time coincident with the largest flare ever observed for this source at millimeter wavelengths. Changes in the position angle of this component, as well as a progressive rotation of its magnetic polarization vector, suggest the presence of a twisted (resembling a helix in projection) configuration of the underlying jet magnetic field and jet geometry. We identify several knots that appear in the wake of the new superluminal component, moving at proper motions ∼4 times slower than any of the other moving knots observed in 3C 120. These features have properties similar to those of the "trailing" shocks seen in relativistic, time-dependent, hydrodynamical, and emission simulations of compact jets. Such trailing compressions are triggered by pinch-mode jet-body instabilities caused by the propagation of a strong perturbation, which we associate with the new strong superluminal component.

KW - Galaxies: Active

KW - Galaxies: Individual (3C 120)

KW - Galaxies: Jets

KW - Polarization radio continuum: Galaxies

UR - http://www.scopus.com/inward/record.url?scp=0043134897&partnerID=8YFLogxK

U2 - 10.1086/324759

DO - 10.1086/324759

M3 - Article

AN - SCOPUS:0043134897

VL - 561

SP - L161-L164

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 PART II

ER -