2003MNRAS.338L..19W

We present XMM-Newton observations of two hyperluminous IRAS galaxies (L_Bol>10¹³h^–2₅₀L_☉), 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) =2.1x10⁴²erg.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(2-10keV)≳1.8x10⁴⁴erg.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> 1.5x10²⁴ 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.