XMM-Newton observations of broad iron Kα emission from Seyfert 1.9 galaxy MCG-5-23-16

XMM-Newton observations of the bright Seyfert 1.9 galaxy MCG - 5-23-16 have revealed a broad Fe Kalpha emission line that is nearly symmetric in contrast to the broad and redshifted asymmetric Fe Kalpha line sometimes observed from Seyfert 1 galaxies. The Fe Kalpha line has two distinct components - a narrow unresolved component with an equivalent width of similar to40 eV and a broad component with a FWHM of similar to40,000 km s(-1) and an equivalent width of similar to120 eV. An absorption feature at similar to7.1 keV has also been observed. The energies of the emission and absorption features are consistent with those arising from neutral iron. The broad component is consistent with a Fe Kalpha emission line expected from a relativistic accretion disk around a Schwarzschild or Kerr black hole. Alternatively, most of the flux in the broad component could also be modeled as reflection emission, which mimics emission line - like features because of the presence of iron K-shell edge at similar to7.1 keV; however, the reflection fraction, R similar to 3, is much higher than that inferred from the BeppoSAX observations (R similar to 0: 5). The disk inclination angle of similar to47degrees, inferred from the disk-line fits, and the absorption column (N-H similar to10(22) cm(-2)), inferred from the low-energy spectral curvature due to photoelectric absorption, suggest that our line of sight passes through the outer edge of a putative torus and are consistent with those expected for a Seyfert 1.9 galaxy falling within the unification scheme. The strength of the narrow iron Kalpha emission and the optical depth of the iron K absorption edge suggest their origin in the putative torus with N-H similar to 10(24) cm(-2) in the inner regions and N-H similar to 10(22) cm(-2) in the outer edges. The strength of the broad component of Fe Kalpha varied by a factor of similar to2 between the two XMM-Newton observations taken similar to6 months apart, while the narrow component of Fe Kalpha and the continuum flux did not appear to vary appreciably. There is evidence for a weakening in the strength of the broad iron Kalpha emission with the flattening of the observed continuum. This can perhaps be explained if the shape of the continuum is coupled with the ionization stage of the reflector.