RXTE observation of NGC 6240:: a search for the obscured active nucleus

The wide-band energy spectrum of NGC 6240 over the range 0.5-200 keV is investigated using the RXTE and ASCA data. The RXTE data provide the spectrum beyond the ASCA range (0.5-10 keV) with significant detection of signals up to 30 keV and upper limits above 20 keV. The spectrum above 10 keV is found to be very flat. A strong iron K emission line discovered in the previous ASCA observation is also confirmed with the RXTE Proportional Counter Array (PCA), These results provide further evidence for the dominance of a reflection component, i.e, emission from cool material illuminated by an active galactic nucleus (AGN). By fitting the spectra obtained with RXTE and ASCA simultaneously, we satisfactorily modelled the AGN spectrum with a Compton reflection component and probably a transmitted AGN component penetrating through a thick absorber. The X-ray luminosity of the AGN is estimated to be in the range 4 x 10(43) to 6 x 10(44) erg s(-1) in the range 2-10 keV, which categorizes NGC 6240 among the most luminous Seyfert nuclei. The ratio of the 2-10 keV X-ray luminosity to the infrared luminosity, L-x(2-10 keV)/L-IR, is 0.01-0.1, which implies a quite substantial, if not dominant, contribution of AGN to the infrared luminosity.