2026ApJ..1000..107R

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 ($a={\rm{0}}.4{3}_{-0.14}^{+0.10}$) 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 ${M}_{{\rm{BH}}}=0.2{9}_{-0.16}^{+0.01}\times 1{0}^{8}{M}_{\odot }$, comparable to the previous measurement, and a coronal height $h=2.5{9}_{-0.33}^{+5.17}{r}_{{\rm{g}}}$. 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.