Tracing Fe K X-Ray Reverberation Lag in the Energy-resolved Spectra of Narrow-line Seyfert 1 Galaxy Ton S180

Abstract We report the Fe K relativistic reverberation feature for the first time in the narrow-line Seyfert 1 galaxy Ton S180. Using a long observation from XMM-Newton we find that the Fe K emission lag peaks at 117 ± 49 s in the lag energy spectrum computed for frequencies (0.3–8.5) × 10 −4 Hz. The lag amplitude drops to 22.85 ± 14.20 s as the frequency increases to (8.5–30) × 10 −4 Hz. The time-averaged spectrum of the source shows a relatively narrow Fe K line at ∼6.4 keV, indicating a low black hole spin ( a = 0 . 4 3 − 0.14 + 0.10 ) based on the reflection modeling. We perform general relativistic transfer function modeling of the lag energy spectra individually. This provides an independent timing-based measure of the spin at a = 0.3 0 − 0.17 + 0.34 , a black hole mass M BH = 0.2 9 − 0.16 + 0.01 × 1 0 8 M ⊙ , comparable to the previous measurement, and a coronal height h = 2.5 9 − 0.33 + 5.17 r g . Further, we observe that the Fe K lag and the black hole mass fit well in the linear lag–mass relation shown by other Seyfert 1 galaxies.