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One distinctive feature of low-luminosity active galactic nuclei (LLAGN) isthe relatively weak reflection features they may display in the X-ray spectrum,which can result from the disappearance of the torus with decreasing accretionrates. Some material, however, must surround the active nucleus, i.e., theaccretion flow itself and, possibly, a flattened-out or thinned torus. In thiswork, we study whether reflection is indeed absent or undetectable due to itsintrinsically weak features together with the low statistics inherent to LLAGN.Here we focus on NGC 3718 ($L/L_{\rm Edd}\sim10^{-5}$) combining observationsfrom XMM--Newton and the deepest to date NuSTAR (0.5--79 keV) spectrum of aLLAGN, to constrain potential reflectors, and analyze how the fitted coronalparameters depend on the reflection model. We test models representing both anaccretion disc (Relxill) and a torus-like (MYTorus and Borus) neutralreflector. From a statistical point of view, reflection is not required, butits inclusion allows to place strong constraints on the geometry and physicalfeatures of the surroundings: both neutral reflectors (torus) tested should beCompton thin ($N_H<10^{23.2}$cm$^{-2}$) and preferentially cover a largefraction of the sky. If the reflected light instead arises from an ionizedreflector, a highly ionized case is preferred. These models produce anintrinsic power-law spectral index in the range [1.81--1.87], where the torusmodels result in steeper slopes. The cut-off energy of the power-law emissionalso changes with the inclusion of reflection models, resulting in constrainedvalues for the disc reflectors and unconstrained values for torus reflectors.

Constraining X-ray reflection in the low-luminosity AGN NGC 3718 using NuSTAR and XMM--Newton