Volume 489, Number 2, October II 2008
|Page(s)||L21 - L24|
|Published online||11 September 2008|
Letter to the Editor
The magnetic field and the location of the TeV emitter in Cygnus X-1 and LS 5039
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
Accepted: 15 August 2008
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
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.