Issue |
A&A
Volume 559, November 2013
|
|
---|---|---|
Article Number | A75 | |
Number of page(s) | 11 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201321858 | |
Published online | 18 November 2013 |
The TeV blazar Markarian 421 at the highest spatial resolution⋆,⋆⋆
1
INAF Istituto di Radioastronomia, via Gobetti 101,
40129
Bologna n
Italy
e-mail: mariagrazia.blasi@studio.unibo.it
2
Dipartimento di Fisica e Astronomia, Università di
Bologna, via Ranzani
1, 40127
Bologna,
Italy
3
National Radio Astronomy Observatory, Charlottesville, 520
Edgemont Road, VA
22903-2475,
USA
4
CSIRO Astronomy and Space Science, PO Box 76,
NSW 1710
Epping,
Australia
5
Max-Planck-Institut für Radioastronomie,
Auf dem Hügel 69, 53121
Bonn,
Germany
6
Astro Space Center of Lebedev Physical Institute,
Profsoyuznaya 84/32,
117997
Moscow,
Russia
7
Institute for Astrophysical Research, Boston
University, 725 Commonwealth
Avenue, Boston
MA
02215,
USA
8
Astronomical Institute, St. Petersburg State University,
Universitetskij Pr. 28, 198504
St Petersburg,
Russia
9
ISAS/JAXA, 3-1-1 Yoshinodai, Chuo-ku, 252-5210
Sagamihara,
Japan
10
Max-Planck-Institut für Physik, Föhringer Ring 6, 80805
München,
Germany
11
Instituto de Astrofísica de Andalucía,
IAA-CSIC, Apdo. 3004,
18080
Granada,
Spain
12
Department of Physics and Astronomy, Whittier College, 13406 E. Philadelphia Street,
Whittier
CA
90608,
USA
13
Sternberg Astronomical Institute, Moscow State University,
Universitetskij prosp. 13, 119992
Moscow,
Russia
Received: 8 May 2013
Accepted: 6 August 2013
Context. High-resolution radio observations allow us to directly image the innermost region of active galactic nuclei. The Very Long Baseline Array (VLBA) data analyzed in this paper were obtained during a multiwavelength (MWL) campaign, carried out in 2011, from radio to very high energy gamma rays, on the TeV blazar Markarian 421 (Mrk 421).
Aims. Our aim was to obtain information on the jet structure in Mrk 421 during the MWL campaign at the highest possible angular resolution and with high temporal frequency observations, in order to compare structural and flux density evolution with higher energy variations.
Methods. We consider data obtained with the VLBA at 43 GHz through two sets of observations: one is part of a dedicated multi-frequency monitoring campaign, in which we observed Mrk 421 once a month from January to December 2011 at three frequencies; the other is extracted from the Boston University monitoring program, which observes 34 blazars at 43 GHz about once per month. We model-fit the data in the visibility plane, study the proper motion of jet components, the light curve, and the spectral index of the jet features. We compare the radio data with optical light curves obtained at the Steward Observatory, considering also the optical polarization information.
Results. Mrk 421 has a bright nucleus and a one-sided jet extending towards the north-west for a few parsecs. The model-fits show that brightness distribution is well described using 6–7 circular Gaussian components, four of which are reliably identified at all epochs; all components are effectively stationary except for component D, at ~0.4 mas from the core, whose motion is, however, subluminal. Analysis of the light curve shows two different states, with the source being brighter and more variable in the first half of 2011 than in the second half. The highest flux density is reached in February. A comparison with the optical data reveals an increase of the V magnitude and of the fractional polarization simultaneous with the enhancement of the radio activity.
Key words: galaxies: active / BL Lacertae objects: individual: Markarian 421 / galaxies: jets
Table 3 is available in electronic form at http://www.aanda.org
VLBA images are only available as FITS files at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/559/A75
© ESO, 2013
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.