EDP Sciences
Free access
Volume 445, Number 3, January III 2006
Page(s) 1089 - 1092
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20053189

A&A 445, 1089-1092 (2006)
DOI: 10.1051/0004-6361:20053189

The broad-band spectrum of Cyg X-2 with INTEGRAL

G. Lavagetto1, T. Di Salvo1, M. Falanga2, R. Iaria1, N. R. Robba1, L. Burderi3, W. H. G. Lewin4, M. Méndez5, L. Stella6 and M. van der Klis7

1  Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, via Archirafi 36, 90123 Palermo (PA), Italy
    e-mail: lavaget@fisica.unipa.it
2  CEA Saclay, DSM/DAPNIA/Service d'Astrophysique (CNRS FRE 2591), 91191 Gif-sur-Yvette, France
3  Università degli Studi di Cagliari, Dipartimento di Fisica, SP Monserrato-Sestu, KM 0.7, 09042 Monserrato, Italy
4  Center for Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
5  SRON, National Institute for Space Research, 3584 CA, Utrecht, The Netherlands
6  Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Roma, Italy
7  Astronomical Institute "Anton Pannekoek", University of Amsterdam, and Center for High Energy Astrophysics, Kruislaan 403, 1098 SJ, Amsterdam, The Netherlands

(Received 4 April 2005 / Accepted 14 September 2005)

We study the broad band (3-100 keV) spectrum of Cygnus X-2 with INTEGRAL. We find that the spectrum is well fitted by a Comptonized component with a seed-photons temperature of $\sim $1 keV, an electron temperature of $\sim $3 keV and an optical depth $\tau \sim 8$. Assuming spherical geometry, the radius of the seed-photons emitting region is $\sim $17 km. The source shows no hard X-ray emission; it was detected only at a $3 \sigma$ level above 40 keV. We also analyzed public ISGRI data of Cyg X-2 to investigate the presence of a hard X-ray component. We report the possible presence of hard X-ray emission in one data set.

Key words: accretion, accretion disks -- binaries: close -- stars: individual: Cygnus X-2 -- stars: neutron

SIMBAD Objects

© ESO 2006