Letter to the Editor

First INTEGRAL observations of Cygnus X-3^*

¹ Science Data Center, Chemin d'Écogia 16, 1290 Versoix, Switzerland
² Observatory, PO Box 14, 00014 University of Helsinki, Finland
³ Centrum Astronomiczne im. M. Kopernika, Bartycka 18, 00-716 Warszawa, Poland
⁴ CNR-IASF, Sezione di Milano, via Bassini 15, 20133 Milano, Italy
⁵ Smithsonian Astrophysical Observatory, 60 Garden Street, MS 67, Cambridge, MA 02138-1516, USA
⁶ Institut für Astronomie and Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
⁷ Geneva Observatory, Ch. des Maillettes 51, 1290 Sauverny, Switzerland
⁸ Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁹ Centre d'Études de Saclay, DAPNIA/Service d'Astrophysique, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
¹⁰ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
¹¹ Danish Space Research Institute, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark

Corresponding author: O. Vilhu, osmi.vilhu@helsinki.fi

Received: 15 July 2003
Accepted: 18 August 2003

Abstract

We present the first INTEGRAL results on Cyg X-3 from the PV phase observations of the Cygnus region. The source was clearly detected by the JEM-X, ISGRI and SPI. The INTEGRAL observations were supported by simultaneous pointed RXTE observations. Their lightcurves folded over the 4.8 hour binary period are compatible with the mean RXTE/ASM and CGRO/BATSE light curves. We fit our broad-band X-ray/γ-ray spectra with a physical model, which represents the first such published model for Cyg X-3. The main physical processes in the source are thermal Comptonization and Compton reflection with parameters similar to those found for black-hole binaries at high Eddington rates.