We report the discovery of a Compton-thick AGN and of intense star-formation activity in the nucleus and disk , respectively , of the nearly edge-on superwind galaxy NGC 4666 .
Spatially unresolved emission is detected by BeppoSAX only at energies < 10 keV , whereas spatially resolved emission from the whole disk is detected by XMM-Newton .
A prominent ( EW \sim 1 - 2 keV ) emission line at \sim 6.4 keV is detected by both instruments .
From the XMM-Newton data alone the line is spectrally localized at E \simeq 6.42 \pm 0.03 keV , and seems to be spatially concentrated in the nuclear region of NGC 4666 .
This , together with the presence of a flat ( \Gamma \sim 1.3 ) continuum in the nuclear region , suggests the existence of a strongly absorbed ( i.e. , Compton-thick ) AGN , whose intrinsic 2-10 keV luminosity is estimated to be L _ { 2 - 10 } \raise - 2.0 pt \hbox { \hbox to 0.0 pt { \hbox { $ \sim$ } } \raise 5.0 pt \hbox { $ > $ } % } 2 \times 10 ^ { 41 } erg s ^ { -1 } .
At energies \sim < 1 keV the integrated ( BeppoSAX ) spectrum is dominated by a \sim 0.25 keV thermal gas component distributed throughout the disk ( resolved by XMM-Newton ) .
At energies \sim 2-10 keV , the integrated spectrum is dominated by a steep ( \Gamma \raise - 2.0 pt \hbox { \hbox to 0.0 pt { \hbox { $ \sim$ } } \raise 5.0 pt \hbox { $ > $ } } 2 ) power-law ( PL ) component .
The latter emission is likely due to unresolved sources with luminosity L \sim 10 ^ { 38 } -10 ^ { 39 } erg s ^ { -1 } that are most likely accreting binaries ( with BH masses \leq 8 M _ { \odot } ) .
Such binaries , which are known to dominate the X-ray point-source luminosity in nearby star-forming galaxies , have \Gamma \sim 2 PL spectra in the relevant energy range .
A \Gamma \sim 1.8 PL contribution from Compton scattering of ( the radio-emitting ) relativistic electrons by the ambient FIR photons may add a truly diffuse component to the 2-10 keV emission .