Multi-epoch Detection of an Ultra-fast Inflow in ESP 39607: Evidence for an Accretion Cascade

Abstract: We present simultaneous XRISM, XMM-Newton, and NuSTAR observations of ESP 39607, a Seyfert 2 galaxy at $z = 0.201$. XRISM/Resolve reveals two absorption features near 4.7 and 4.9 keV in the observed frame, consistent with redshifted Fe XXV He-$α$/Fe XXVI Ly-$α$ absorption from gas inflowing at $v_{\rm in} \simeq 0.16c$. The high velocity identifies the absorber as an ultra-fast inflow (UFI), which is detected at $\sim 3$-$3.7σ$ across different methods and continuum models. Photoionization modeling yields $\log ξ/{\rm erg\,s^{-1}\,cm} \simeq 3.7$-$3.8$ and a column density $$\log N_{\rm H,abs}/{\rm cm^{-2}} \simeq 23.2$$-$23.8$, the latter depending on the assumed metallicity. The inflow velocity and line properties are consistent with those reported from two earlier NuSTAR epochs, indicating that similar inflowing material was present over a baseline of at least 2.2 yr in the source rest frame. Across all three epochs, the combined detection significance of the UFI is $5.3σ$. Given the dynamical timescale of a few days at the inferred radius, $R \simeq 49$-$77\,R_{\rm g}$, the multi-year evidence favors a scenario in which the inflow is continuously replenished, forming an accretion "cascade", rather than a single long-lived cloud. With an estimated mass inflow rate of $\dot{M}<em>{\rm in} \simeq 0.3$-$1.4\,M</em>\odot$ yr$<sup>{-1}$, depending on metallicity, and a ratio $$\dot{M}<em>{\rm in}/\dot{M}</em>{\rm acc} \simeq 0.2$$-$1.0$, the inflow could supply a substantial fraction of the accretion needed to power the central active galactic nucleus.