Dramatic X-ray Spectral Variability of Mkn 841

Summary

We present the results from a detailed analysis of the X-ray spectral variability of Mkn 841 based on EXOSAT, Ginga and ROSAT observations over the period 1984 June to 1990 July.

Variability is apparent in both the soft (0.1–1.0 keV) and medium (1–20 keV) energy bands (Fig. 1). Above 1keV, the spectra are adequately modelled by a power-law with a strong emission line (of equivalent width ∼ 450 eV). The energy of the line (∼ 6.4 keV) is indicative of K-shell fluorescence from neutral iron, leading to the interpretation that the line arises via X-ray illumination of cold material within the accretion flow. In addition to the flux variability, the continuum shape also changes in a dramatic fashion, with variations in the apparent photon index ΔГ ∼ 0.6.

The large equivalent width of the emission line suggests an enhanced reflection component in this source, compared to other Seyferts observed with Ginga. The spectral changes are interpreted in terms of variable power-law continuum superimposed on the flatter refection component. For one Ginga observation, the reflected flux appears to dominate the medium energy X-ray emission, resulting in an unusually flat slope (Г ∼ 1.0).

The soft X-ray excess reported by Arnaud et al. (1987), is found to be highly variable by a factor ∼ 10. No evidence is found for an intrinsic column density n_H ≲ few 10²⁰ cm⁻².