EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 457/2 Article
Free access article

Issue A&A
Volume 457, Number 2, October II 2006
Page(s) 455 - 465
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20054078



A&A 457, 455-465 (2006)
DOI: 10.1051/0004-6361:20054078

Simultaneous radio-interferometric and high-energy TeV observations of the $\mathsf{\gamma}$-ray blazar Mkn 421

P. Charlot1, D. C. Gabuzda2, H. Sol3, B. Degrange4 and F. Piron5

1  Observatoire de Bordeaux (OASU) - CNRS/UMR 5804, BP 89, 33270 Floirac, France
    e-mail: charlot@obs.u-bordeaux1.fr
2  University College Cork - Physics Department, Cork, Ireland
3  Observatoire de Paris - CNRS/UMR 8631, 92195 Meudon Cedex, France
4  École Polytechnique - Laboratoire Leprince-Ringuet, 91128 Palaiseau, France
5  Université de Montpellier II, LPTA - CNRS/UMR 5207, Place Bataillon, 34095 Montpellier Cedex 5, France

(Received 20 August 2005 / Accepted 21 April 2006 )

Abstract
The TeV-emitting BL Lac object Mkn 421 was observed with very long baseline interferometry (VLBI) at three closely-spaced epochs one-month apart in March-April 1998. The source was also monitored at very-high $\gamma$-ray energies (TeV measurements) during the same period in an attempt to search for correlations between TeV variability and the evolution of the radio morphology on parsec scales. While the VLBI maps show no temporal changes in the Mkn 421 VLBI jet, there is strong evidence of complex variability in both the total and polarized fluxes of the VLBI core of Mkn 421 and in its spectrum over the two-month span of our data. The high-energy measurements indicate that the overall TeV activity of the source was rising during this period, with a $\gamma$-ray flare detected just three days prior to our second VLBI observing run. Although no firm correlation can be established, our data suggest that the two phenomena (TeV activity and VLBI core variability) are connected, with the VLBI core at 22 GHz being the self-absorbed radio counterpart of synchrotron self-Compton (SSC) emission at high energies. Based on the size of the VLBI core, we could derive an upper limit of 0.1 pc (3 $\times$ 1017 cm) for the projected size of the SSC zone. This determination is the first model-free estimate of the size of the $\gamma$-ray emitting region in a blazar.


Key words: galaxies: active -- galaxies: jets -- BL Lacertae objects: individual: Mkn 421 -- radio continuum: galaxies -- techniques: high angular resolution -- gamma rays: observations



© ESO 2006


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.