The broad-band X-ray spectral variability of Mrk 841

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Abstract
The results of a detailed spectral analysis of four X-ray observations of the luminous Seyfert 1.5 galaxy Mrk 841, performed using the EXOSAT and Ginga satellites over the period 1984 June to 1990 July, are reported. Preliminary results from a short ROSAT PSPC observation of Mrk 841 in 1990 July are also presented. Variability is apparent in both the soft (0.1–1.0 keV) and medium (1–20 keV) energy bands. Above 1 ke V, 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 surrounding the source. In addition to the flux variability, the continuum shape also changes in a dramatic fashion, with variations in the apparent photon index ∆Г~ 0.6. The large equivalent width of the emission line clearly indicates a strongly enhanced reflection component in this source, compared to other Seyferts observed with Ginga. The spectral changes are interpreted in terms of a variable power-law continuum superimposed on a flatter reflection 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. is found to be highly variable by a factor ~ 10. These variations are not correlated with the hard flux, but it seems likely that the soft component arises via reprocessing of the hard X-rays. We find no evidence for intrinsic absorption, with the equivalent hydrogen column density constrained to be ≲ few ×1020 cm–2. The implications of these results for physical models of the emission regions in this and other X-ray bright Seyferts are briefly discussed.

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