We briefly review and extend our discussion of the ROSAT detection of the extraordinarily luminous ( > 10 ^ { 42 } erg/s ) partly extended ( > 30 kpc diameter ) X-ray emission from the double-nucleus ultraluminous infrared galaxy ( ULIRG ) NGC 6240 .
The ROSAT spectrum can be well fit by emission from two components in roughly equal proportions : a thermal optically thin plasma with kT \sim 0.6 keV and a hard component that can be represented by a canonical AGN powerlaw .
Source counts appear to have dropped by 30 % within a year .
Altogether , these findings can be well explained by a contribution of radiation from an AGN essentially hidden at other wavelengths .
Fits of ASCA spectra , conducted by various groups , corroborate this result , revealing a high-equivalent width FeK \alpha blend which again is straightforwardly interpreted by scattered AGN light .

If radiating at the Eddington limit , the central black hole mass does not exceed \sim 10 ^ { 7 } M _ { \sun } .
We discuss implications for the formation of this AGN .
However , the luminosity in the remaining extended thermal component is still at the limits of a pure starburst-wind-induced source .
We suggest that the deeply buried starburst has switched to a partially dormant phase so that heating of the outflow is diminished and a cooling flow could have been established .
This flow may account for the extended shock heating traced by LINER-like emission line ratios and the extremely luminous H _ { 2 } 2.121 \mu m emission from the central region of this galaxy .
Next-generation X-ray telescopes will be able to test this proposal .