We present new XMM-Newton observation of the Ultra Luminous Infrared Galaxy ( ULIRG ) NGC 6240 .
We analyze the reflecting grating spectrometer ( RGS ) data , and data from the other instruments , and find a starburst dominated 0.5–3 keV spectrum with global properties resembling those observed in M82 but with a much higher luminosity .
We show that the starburst region can be divided into an outer zone , beyond a radius of about 2.1 kpc , with a gas temperature of about 10 ^ { 7 } K and a central region with temperatures in the range ( 2–6 ) \times 10 ^ { 7 } K. The gas in the outer region emits most of the observed O viii L _ { \alpha } line and the gas in the inner region the emission lines of higher ionization ions , including a strong Fe xxv line .
We also identify a small inner part , very close to the active nuclei , with typical Seyfert 2 properties including a large amount of photoionized gas producing a strong Fe K \alpha 6.4 keV line .
The combined abundance , temperature and emission measure analysis indicates super solar Ne/O , Mg/O , Si/O , S/O and possibly also Fe/O .
The analysis suggests densities in the range of ( 0.07–0.28 ) \epsilon ^ { -1 / 2 } cm ^ { -3 } and a total thermal gas mass of \sim 4 \times 10 ^ { 8 } \epsilon ^ { 1 / 2 } M _ { \odot } , where \epsilon is the volume filling factor .
We used a simple model to argue that a massive starburst with an age of \simeq 2 \times 10 ^ { 7 } years can explain most of the observed properties of the source .
NGC 6240 is perhaps the clearest case of an X-ray bright luminous AGN , in a merger , whose soft X-ray spectrum is dominated by a powerful starburst .