INTEGRAL observations of Scorpius X-1: evidence for Comptonization up to 200 keV

Instituto Nacional de Pesquisas Espaciais – INPE Avenida dos Astronautas 1758, 12227-010 São José dos Campos-SP, Brazil
e-mail: tais.maiolino@das.inpe.br; damico@das.inpe.br; braga@das.inpe.br

Received: 31 October 2012
Accepted: 22 January 2013

Abstract

We have analyzed a long-term database for Sco X-1 obtained with the telescope IBIS onboard the INTEGRAL satellite in order to study the hard X-ray behavior of Sco X-1 from 20 up to 200 keV. Besides the data used for producing of the INTEGRAL catalog of sources, this is the longest (412 ks) database of IBIS on Sco X-1 up to date. The production of hard X-ray tails in low-mass X-ray binaries is still a matter of debate. Since most of the fits to the high-energy part of the spectra are done with powerlaw models, the physical mechanism for the hard X-ray tail production is unclear. The purpose of this study is to better constrain those possible mechanisms. Our main result shows a strong correlation between the fluxes in the thermal and nonthermal part of Sco X-1 spectra. We, thus, suggest that comptonization of lower energy photons is the mechanism for producing hard X-ray tails in Sco X-1.