XMM-Newton observations of two hyperluminous IRAS galaxies: Compton-thick quasars with obscuring starbursts

We present XMM-Newton observations of two hyperluminous IRAS galaxies (L_Bol > 10¹³h^-2₅₀ L_solar), neither of which were previously detected by ROSAT. Published models of the infrared spectral energy distributions imply that a starburst and obscured quasar contribute equally to the power of each source. IRAS F12514+1027 (z= 0.30) is detected in 18.6 ks with 130 EPIC-pn counts over 0.2-12 keV. The soft X-ray spectrum exhibits thermal emission from the starburst, with T~= 0.3 keV and L (0.5-2.0 keV) =2.1 × 10⁴² erg s^-1. With its Fe K-edge, the flat continuum above 2 keV is interpreted as cold reflection from a hidden AGN of intrinsic L (2-10 keV) >~ 1.8 × 10⁴⁴ erg s^-1. Comparison with the infrared power requires that the X-ray reflector subtend ~2π/5 sr at the central engine. IRAS F00235+1024 (z= 0.575) is not detected by the EPIC-pn in 15.9 ks; the limits imply that the starburst is X-ray weak, and (for the AGN) that any hard X-ray reflector subtend <2π/5 sr. The direct lines of sight to the AGN in both objects are Compton-thick (N_H > 1.5 × 10²⁴ cm^-2), and the presence of a reflection component in F12514+1027, but not in F00235+1024, suggests that the AGN in the latter object is more completely obscured. This is consistent with their Seyfert-2 and starburst optical spectra, respectively.