XMM-Newton and NuSTAR joint observations of Mrk 915: a deep look into the X-ray properties

Abstract

We report on the X-ray monitoring programme (covering slightly more than 11 d) carried out jointly by XMM-Newton and NuSTAR on the intermediate Seyfert galaxy Mrk 915. The light curves extracted in different energy ranges show a variation in intensity but not a significant change in the spectral shape. The X-ray spectra reveal the presence of a two-phase warm absorber: a fully covering mildly ionized structure [log ξ/(erg cm s^-1) ∼ 2.3, N_H∼ 1.3 × 10^21cm^-2] and a partial covering (∼90 per cent) lower ionized one [log ξ/(erg cm s^-1) ∼ 0.6, N_H∼ 2 × 10^22 cm^-2]. A reflection component from distant matter is also present. Finally, a high-column density (N_H ∼ 1.5 × 10^23 cm^-2) distribution of neutral matter covering a small fraction of the central region is observed, almost constant, in all observations. The main driver of the variations observed between the data sets is a decrease in the intrinsic emission by a factor of ∼1.5. Slight variations in the partial covering ionized absorber are detected, while the data are consistent with no variation of the total covering absorber. The most likely interpretation of the present data locates this complex absorber closer to the central source than the narrow line region, possibly in the broad line region, in the innermost part of the torus, or in between. The neutral obscurer may either be part of this stratified structure or associated with the walls of the torus, grazed by (and partially intercepting) the line of sight.