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

Aims. We report the detection of hard X-ray emission from the field o f the star-forming region NGC 6334with the the International Gamma-Ray Astrophysics Laboratory INTEGRAL. Methods. The JEM-X monitor and ISGRI imager aboard INTEGRAL and Chandra ACISimager 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 6334ridge. The 20-60 keV flux from the source is (1.8±0.37)×10 −11 erg cm −2 s −1 . 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 extrapolatio ns of X-ray imaging observations of NGC 6334by Chandra ACISand 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 accelerat ion in energetic outflows from massive early type stars. The p ossibility of emission from a young supernova remnant, as suggested by earlier infrared observations of NGC 6334 , is constrained by the non-detection of 44 Ti lines.