Simultaneous NuSTAR and XMM-Newton 0.5-80 keV spectroscopy of the narrow-line Seyfert 1 galaxy SWIFT J2127.4+5654

We present a broad-band spectral analysis of the joint XMM-Newton and Nuclear Spectroscopic Telescope Array observational campaign of the narrow-line Seyfert 1 SWIFT J2127.4+5654, consisting of 300 ks performed during three XMM-Newton orbits. We detect a relativistic broadened iron Kα line originating from the innermost regions of the accretion disc surrounding the central black hole, from which we infer an intermediate spin of a = 0.58−0.17+0.11.

The intrinsic spectrum is steep (Γ = 2.08 ± 0.01) as commonly found in narrow-line Seyfert 1 galaxies, while the cutoff energy (Ec = 108−10+11 keV) falls within the range observed in broad-line Seyfert 1 galaxies. We measure a low-frequency lag that increases steadily with energy, while at high frequencies, there is a clear lag following the shape of the broad Fe K emission line.

Interestingly, the observed Fe K lag in SWIFT J2127.4+5654 is not as broad as in other sources that have maximally spinning black holes. The lag amplitude suggests a continuum-to-reprocessor distance of about 10-20 rg. These timing results independently support an intermediate black hole spin and a compact corona.