XMM–Newton observations of the interacting galaxy pairs NGC 7771/0 and NGC 2342/1

We present XMM–Newton X‐ray observations of the interacting galaxy pairs NGC 7771/7770 and NGC 2342/2341. In NGC 7771, for the first time we are able to resolve the X‐ray emission into a bright central source plus two bright ( L X > 10 40 erg s −1 ) ultraluminous X‐ray sources (ULXs) located either end of the bar. In the bright central source ( L X ∼ 10 41 erg s −1 ) , the soft emission is well‐modelled by a two‐temperature thermal plasma with kT = 0.4/0.7 keV . The hard emission is modelled with a flat absorbed power‐law (Γ∼ 1.7, N H ∼ 10 22 cm −2 ) , and this together with a low‐significance (1.7σ) ∼ 300 eV equivalent width emission line at ∼6 keV are the first indications that NGC 7771 may host a low‐luminosity AGN. For the bar ULXs, a power‐law fit to X‐1 is improved at the 2.5σ level with the addition of a thermal plasma component ( kT ∼ 0.3 keV) , while X‐2 is improved only at the 1.3σ level with the addition of a disc blackbody component with T in ∼ 0.2 keV . Both sources are variable on short time‐scales implying that their emission is dominated by single accreting X‐ray binaries (XRBs). The three remaining galaxies, NGC 7770, NGC 2342 and NGC 2341, have observed X‐ray luminosities of 0.2, 1.8 and 0.9 × 10 41 erg s −1 , respectively (0.3–10 keV). Their integrated spectra are also well‐modelled by multi‐temperature thermal plasma components with kT = 0.2–0.7 keV , plus power‐law continua with slopes of Γ= 1.8–2.3 that are likely to represent the integrated emission of populations of XRBs as observed in other nearby merger systems. A comparison with other isolated, interacting and merging systems shows that all four galaxies follow the established correlations for starburst galaxies between X‐ray, far‐infrared and radio luminosities, demonstrating that their X‐ray outputs are dominated by their starburst components.