EDP Sciences
Free access
Volume 396, Number 2, December III 2002
Page(s) 615 - 621
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20021428

A&A 396, 615-621 (2002)
DOI: 10.1051/0004-6361:20021428

Rapidly evolving circularly polarized emission during the 1994 outburst of GRO J1655-40

J.-P. Macquart1, K. Wu2, R. J. Sault3 and D. C. Hannikainen4, 5

1  Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
2  Mullard Space Science Laboratory, University College London, Holmbury St Mary, Surrey RH5 6NT, UK, and School of Physics A28, University of Sydney, NSW 2006, Australia
    e-mail: kw@mssl.ucl.ac.uk
3  Australia Telescope National Facility, Narrabri, NSW 2390, Australia
    e-mail: rsault@atnf.csiro.au
4  Department of Physics and Astronomy, Southampton University, Southampton, SO17 1BJ, UK
5  Observatory, PO Box 14, 00014 University of Helsinki, Finland
    e-mail: diana@astro.helsinki.fi

(Received 11 April 2002 / Accepted 24 September 2002 )

We report the detection of circular polarization during the 1994 outburst of the Galactic microquasar GRO J1655-40. The circular polarization is clearly detected at 1.4 and 2.4 GHz, but not at 4.8 and 8.4 GHz, where its magnitude never exceeds 5 mJy. Both the sign and magnitude of the circular polarization evolve during the outburst. The time dependence and magnitude of the polarized emission can be qualitatively explained by a model based on synchrotron emission from the outbursts, but is most consistent with circular polarization arising from propagation effects through the relativistic plasma surrounding the object.

Key words: black hole physics -- galaxies: active -- galaxies: jets -- polarization -- radio continuum: galaxies -- X-rays: individual: GRO J1655-40

Offprint request: J.-P. Macquart, jpm@astro.rug.nl

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