We present an X-ray spectroscopic study of the prototype far-infrared galaxy NGC 6240 from ASCA. The soft X-ray spectrum (below 2 keV) shows clear signatures of thermal emission well described by a multitemperature optically thin plasma, which probably originates in a powerful starburst. Strong hard X-ray emission is also detected with ASCA and its spectrum above 3 keV is extremely flat with a prominent iron K line complex, very similar to that seen in the Seyfert 2 galaxy NGC 1068 but about an order of magnitude more luminous (L3−10keV ≈ 1.4 × 1042 erg s−1). The hard X-ray spectrum indicates that only reflected X-rays of an active galactic nucleus (AGN) buried in a heavy obscuration (NH > 2 × 1024 cm−2) are visible. This is evidence for an AGN in NGC 6240, emitting possibly at a quasar luminosity (∼ 1045 erg s−1), and suggests its significant contribution to the far-infrared luminosity.
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Iwasawa et al. (1998) studied this question.