INTEGRAL detection of hard X-rays from NGC 6334: nonthermal emission from colliding winds or an AGN?

¹ A. F. Ioffe Institute for Physics and Technology, 26 Polytechnicheskaia, 194021 St. Petersburg, Russia e-mail: byk@astro.ioffe.ru
² CEA-Saclay, DSM/DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette Cedex, France
³ APC-UMR 7164, 11 place M. Berthelot, 75231 Paris, France
⁴ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁵ Department of Physics, University College Dublin, Dublin 4, Ireland
⁶ INTEGRAL Science Data Centre, Chemin d'Écogia 16, 1290 Versoix, Switzerland
⁷ Geneva Observatory, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
⁸ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁹ Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bât. B5c, 4000 Liège, Belgium
¹⁰ Sternberg Astronomical Institute, Moscow State University, 13 Universitetskij, 119899 Moscow, Russia

Received: 1 September 2005
Accepted: 20 December 2005

Abstract

Aims.We report the detection of hard X-ray emission from the field of the star-forming region NGC 6334  with the International Gamma-Ray Astrophysics Laboratory INTEGRAL .Methods.The JEM-X  monitor and ISGRI  imager aboard INTEGRAL  and Chandra  ACIS imager were used to construct 3-80 keV images and spectra of NGC 6334.Results.The 3-10 keV and 10-35 keV images made with JEM-X  show a complex structure of extended emission from NGC 6334. The ISGRI  source detected in the energy ranges 20-40 keV, 40-80 keV, and 20-60 keV coincides with the NGC 6334 ridge. The 20-60 keV flux from the source is (. Spectral analysis of the source revealed a hard power-law component with a photon index about 1. The observed X-ray fluxes are in agreement with extrapolations of X-ray imaging observations of NGC 6334  by Chandra ACIS and ASCA GIS.Conclusions.The X-ray data are consistent with two very different physical models. A probable scenario is emission from a heavily absorbed, compact and hard Chandra  source that is associated with the AGN candidate radio source NGC 6334B. Another possible model is the extended Chandra  source of nonthermal emission from NGC 6334 that can also account for the hard X-ray emission observed by INTEGRAL. The origin of the emission in this scenario is due to electron acceleration in energetic outflows from massive early type stars. The possibility of emission from a young supernova remnant, as suggested by earlier infrared observations of NGC 6334, is constrained by the non-detection of ⁴⁴Ti lines.