EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 489/2 Article
Free access article

Issue A&A
Volume 489, Number 2, October II 2008
Page(s) L21 - L24
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200810645
Published online 11 September 2008



A&A 489, L21-L24 (2008)
DOI: 10.1051/0004-6361:200810645

Letter

The magnetic field and the location of the TeV emitter in Cygnus X-1 and LS 5039

V. Bosch-Ramon1, D. Khangulyan1, and F. A. Aharonian2, 1

1  Max Planck Institut für Kernphysik, Saupfercheckweg 1, Heidelberg 69117, Germany
    e-mail: [vbosch;Dmitry.Khangulyan]@mpi-hd.mpg.de
2  Dublin Institute for Advanced Studies, Dublin, Ireland
    e-mail: Felix.Aharonian@dias.ie

Received 21 July 2008 / Accepted 15 August 2008

Abstract
Context. Cygnus X-1 and LS 5039 are two X-ray binaries observed at TeV energies. Both sources are compact systems, contain jet-like (radio) structures, and harbor very luminous O stars. A TeV signal has been found around the superior conjunction of the compact object in both objects, when the highest gamma-ray opacities are expected.
Aims. We investigate the implications of finding TeV emission from Cygnus X-1 and LS 5039 around the superior conjunction, since this can give information on the system magnetic field and the location of the TeV emitter.
Methods. Using the very high-energy spectra and fluxes observed around the superior conjunction in Cygnus X-1 and LS 5039, we compute the absorbed luminosity that is caused by pair creation in the stellar photon field for different emitter positions with respect to the star and the observer line of sight. The role of the magnetic field and electromagnetic cascading are discussed. For the case of inefficient electromagnetic cascading, the expected secondary synchrotron fluxes are compared with the observed ones at X-ray energies.
Results. We find that, in Cygnus X-1 and LS 5039, either the magnetic field in the star surroundings is much smaller than the one expected for O stars or the TeV emitter is located at a distance >1012 cm from the compact object.
Conclusions. Our results strongly suggest that the TeV emitters in Cygnus X-1 and LS 5039 are located at the borders of the binary system and well above the orbital plane. This would not agree with those models for which the emitter is well inside the system, like the innermost-jet region (Cygnus X-1 and LS 5039; microquasar scenario) or the region between the pulsar and the primary star (LS 5039; standard pulsar scenario).


Key words: gamma rays: theory -- X-rays: binaries -- radiation mechanisms: non-thermal



© ESO 2008


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.