INTEGRAL-ISGRI observations of the CygOB2 region: searching for hard X-ray point sources in a region containing several non-thermal emitting massive stars

De Becker M.$^1$, Rauw G.$^1$, Pittard J.M.$^2$, Sana H.$^3$, Stevens I.R.$^4$, Romero G.E.$^{5,6}$

1 - Institut d'Astrophysique et de G'eophysique, Universit'e de Li`ege, 17, All'ee du 6 Ao^ut, B5c, B-4000 Sart Tilman, Belgium
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 Astronom'{i}cas y Geof'{i}sicas, Universidad Nacional de La Plata, Paseo del Bosque, 1900 La Plata, Argentina
6 - Instituto Argentino de Radioastronom'{i}a, C.C.5, (1894) Villa Elisa, Buenos Aires, Argentina

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, WR140, WR146 and WR147. 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.

Reference: Astronomy and Astrophysics
Status: Manuscript has been accepted