Universität zu Köln

Cohen, M. H., Meier, D. L., Arshakian, T. G., Homan, D. C., Hovatta, T., Kovalev, Y. Y., Lister, M. L., Pushkarev, A. B., Richards, J. L. and Savolainen, T. (2014). STUDIES OF THE JET IN BL LACERTAE. I. RECOLLIMATION SHOCK AND MOVING EMISSION FEATURES. Astrophys. J., 787 (2). BRISTOL: IOP PUBLISHING LTD. ISSN 1538-4357

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Abstract

Parsec-scale VLBA images of BL Lac at 15 GHz show that the jet contains a permanent quasi-stationary emission feature 0.26 mas (0.34 pc projected) from the core, along with numerous moving features. In projection, the tracks of the moving features cluster around an axis at a position angle of -166.degrees 6 that connects the core with the standing feature. The moving features appear to emanate from the standing feature in a manner strikingly similar to the results of numerical two-dimensional relativistic magneto-hydrodynamic(RMHD) simulations in which moving shocks are generated at a recollimation shock (RCS). Because of this, and the close analogy to the jet feature HST-1 in M87, we identify the standing feature in BL Lac as an RCS. We assume that the magnetic field dominates the dynamics in the jet, and that the field is predominantly toroidal. From this we suggest that the moving features are compressions established by slow and fast mode magneto- acoustic MHD waves. We illustrate the situation with a simple model in which the slowest moving feature is a slow-mode wave, and the fastest feature is a fast-mode wave. In the model, the beam has Lorentz factor Gamma(gal)(beam) approximate to 3.5 in the frame of the host galaxy and the fast mode wave has Lorentz factor Gamma(beam)(Fwave) approximate to 1.6 in the frame of the beam. This gives a maximum apparent speed for the moving features, beta(app) = v(app)/c = 10. In this model the Lorentz factor of the pattern in the galaxy frame is approximately three times larger than that of the beam itself.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Cohen, M. H. UNSPECIFIED UNSPECIFIED UNSPECIFIED Meier, D. L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Arshakian, T. G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Homan, D. C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hovatta, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kovalev, Y. Y. UNSPECIFIED UNSPECIFIED UNSPECIFIED Lister, M. L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Pushkarev, A. B. UNSPECIFIED UNSPECIFIED UNSPECIFIED Richards, J. L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Savolainen, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-437119
DOI:	10.1088/0004-637X/787/2/151
Journal or Publication Title:	Astrophys. J.
Volume:	787
Number:	2
Date:	2014
Publisher:	IOP PUBLISHING LTD
Place of Publication:	BRISTOL
ISSN:	1538-4357
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language ACTIVE GALACTIC NUCLEI; HELICAL MAGNETIC-FIELD; LINKING ACCRETION FLOW; COMPACT RADIO-SOURCES; BASE-LINE ARRAY; BLACK-HOLE MASS; RELATIVISTIC JETS; NUMERICAL SIMULATIONS; FARADAY-ROTATION; SCALE JET Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/43711