The NuSTAR View of the Seyfert 2 Galaxy NGC 4388

Abstract

We present an analysis of NuSTAR X-ray observations in the 3–79 keV energy band of the Seyfert 2 galaxy NGC 4388, taken in 2013. The broadband sensitivity of NuSTAR, covering the Fe Kα line and Compton reflection hump, enables tight constraints to be placed on reflection features in AGN X-ray spectra, thereby providing insight into the geometry of the circumnuclear material. In this observation, we found the X-ray spectrum of NGC 4388 to be well described by a moderately absorbed power law with non-relativistic reflection. We fit the spectrum with phenomenological reflection models and a physical torus model and find the source to be absorbed by Compton-thin material (N_H = (6.5 ± 0.8) × 10^(23) cm^(−2)) with a very weak Compton reflection hump (R < 0.09) and an exceptionally large Fe Kα line (EW = 368^(+56)_(-53) eV) for a source with weak or no reflection. Calculations using a thin-shell approximation for the expected Fe Kα EW indicate that an Fe Kα line originating from Compton-thin material presents a possible explanation.