We present Chandra and XMM-Newton observations of the composite star-forming/Seyfert galaxy IRAS20051-1117 .
The X-ray imaging and spectral properties reveal the presence of an active nucleus .
The Chandra image shows a strong nuclear point source ( L ( 2 - 10 keV ) \sim 4 \times 10 ^ { 42 } erg~ { } s ^ { -1 } ) .
The nuclear X-ray source coincides with a bright , also un-resolved , UV source which appears in the XMM-Newton Optical Monitor images .
The XMM-Newton and Chandra spectrum is well represented by a power-law with a photon index of \Gamma \sim 1.7 - 1.9 and a thermal component with a temperature of \sim 0.2 keV .
We also detect an Fe line at 6.4 keV with an equivalent width of \sim 0.3 keV , typical of the iron lines that have been detected in the X-ray spectra of “ classical ” AGN .
We find no evidence for short-term variability in the X-ray light curves , while we detect no variations between the XMM-Newton and Chandra observations which are separated by about 20 days .
Optical spectroscopic observations which were performed \sim 2.5 months after the XMM-Newton observation show that the optical spectrum is dominated by a star-forming galaxy component , although a weak broad H \alpha component is present , in agreement with the results from past observations .
The lack of strong AGN signatures in the optical spectrum of the source can be explained by the dilution of the nuclear AGN emission by the nuclear star-forming component and the strong emission of the underlying , bright host galaxy .