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

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

Abstract

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 ∼1 keV, an electron temperature of ∼3 keV and an optical depth . Assuming spherical geometry, the radius of the seed-photons emitting region is 17 km. The source shows no hard X-ray emission; it was detected only at a 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.