SIMBAD references

Earlier observations of NGC1808 in various wavebands (X-ray, optical, near-infrared, radio) provided evidence for the existence of either a starburst or a Seyfert2 nucleus. We here present the results of multiwavelength XMM-Newton and Chandra observations, which directly prove the co-existence of thermal diffuse plasma and non-nuclear unresolved point-like sources associated with the starburst activity, along with a Low Luminosity Active Galactic Nucleus (LLAGN) or an Ultra Luminous X-ray source (ULX). The broad bandwidth of XMM-Newton allows us to show that the unresolved nuclear source in NGC1808 dominates the hard X-ray spectrum, while the emission in the soft regime, below 1 keV, is dominated by a thermal component associated to an extended starburst. Both EPIC and RGS data provide reliable detections of a number of emission lines from heavy elements, with abundances ranging from roughly 0.7 to 2.2Z_☉ for different elements. However, no 6.4keV Fe Kα fluorescence line emission was detected. The analysis of the nuclear region of NGC1808 allows us to detect and disentangle the contribution of an unresolved nuclear X-ray source and the starburst region, but the exact nature of the nucleus remains unknown. The observed luminosity of NGC1808 is L_2–10keV=(1.61±0.06)x10⁴⁰erg/s. A comparison of our OM 212nm image with a CTIO 4-m telescope Hα frame shows a good general correspondence between the emission from massive stars and warm ionized gas, with minor deviations near the ends of the bar in NGC1808. An aditional, very soft thermal spectral component with kT≃0.1keV has been discovered in the XMM-Newton spectral analysis, which most likely originates from the halo of NGC1808.