Preprint Logo P112 September
2007


To be published in:
Astronomy and Astrophysics

INTEGRAL-ISGRI observations of the Cyg OB2 region:
searching for hard X-ray point sources in a region containing several non-thermal emitting massive stars.

M. De Becker1,*, G. Rauw1,**, J.M. Pittard2 H. Sana3, I.R. Stevens4 and G.E. Romero5,6,***


1 Institut d'Astrophysique et de Géophysique - Université de Liège, Allée du 6 Août, Bât B5c, B-4000 Liège (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, 19 Vitacura, Santiago, 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

* Postdoctoral Researcher FNRS, Belgium
** Research Associate FNRS, Belgium
*** Member of CONICET, Argentina



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.

Key words
Stars: early-type -- Radiation mechanisms: non-thermal -- X-rays: stars -- Gamma rays: observations -- Acceleration of particles

Files
Article: DeBecker-aa7734.pdf (420625 bytes): HTTP FTP (ftp://vela.astro.ulg.ac.be/preprints/)


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