INTEGRAL-ISGRI observations of the Cygnus OB2 region

Searching for hard X-ray point sources in a region containing several non-thermal emitting massive stars

¹ Institut d'Astrophysique et de Géophysique, Université de Liège, 17 allée du 6 Août, B5c, 4000 Sart Tilman, Belgium e-mail: debecker@astro.ulg.ac.be
² School of Physics and Astronomy, The University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
³ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
⁴ School of Physics and Astronomy, University of Birmingham, Edgbaston Birmingham B15 2TT, UK
⁵ Facultad de Ciencias Astronomícas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque, 1900 La Plata, Argentina
⁶ Instituto Argentino de Radioastronomía, C.C.5, (1894) Villa Elisa, Buenos Aires, Argentina

Received: 27 April 2007
Accepted: 8 July 2007

Abstract

Aims.We analyze INTEGRAL-ISGRI data in order to probe the hard X-ray emission (above 20 keV) from point sources in the Cyg OB2 region and to investigate the putative non-thermal high-energy emission from early-type stars (Wolf-Rayet and O-type stars). Among the targets located in the field of view, we focus on the still unidentified EGRET source 3EG 2033+4118 that may be related to massive stars known to produce non-thermal emission in the radio domain, and on the wide colliding-wind binary WR 140.

Methods.Using a large set of data obtained with the IBIS-ISGRI imager onboard INTEGRAL, we run the OSA software package in order to find point sources in the fully coded field of view of the instrument.

Results.Our data do not allow the detection of a lower-energy counterpart of 3EG J2033+4118 nor of any other new point sources in the field of view, and we derive upper limits on the high-energy flux for a few targets: 3EG J2033+4118, TeV J2032+4130, WR 140, WR 146 and WR 147. The results are discussed in the context of the multiwavelength investigation of these objects.

Conclusions.The upper limits derived are valuable constraints for models aimed at understanding the acceleration of particles in non-thermal emitting massive stars, and of the still unidentified very-high gamma-ray source TeV J2032+4130.