A Partial Eclipse of the Heart: The Absorbed X-ray Low State in Mrk 1048

Abstract

We present two new XMM-Newton observations of an unprecedented low flux state in the Seyfert 1 Mrk 1048 (NGC 985), taken in 2013. The X-ray flux below 1 keV drops by a factor of 4-5, whereas the spectrum above 5 keV is essentially unchanged. This points towards an absorption origin for the low state, and we confirm this with spectral fitting, finding that the spectral differences can be well modelled by the addition of a partial covering neutral absorber, with a column density of $\sim3\times 10^{22}$~cm$^{-2}$ and a covering fraction of $\sim0.6$. The optical and UV fluxes are not affected, and indeed are marginally brighter in the more recent observations, suggesting that only the inner regions of the disk are affected by the absorption event. This indicates either that the absorption is due to a cloud passing over the inner disk, obscuring the X-ray source but leaving the outer disk untouched, or that the absorber is dust-free so the UV continuum is unaffected. We use arguments based on the duration of the event and the physical properties of the absorber to constrain its size and location, and conclude that it is most likely a small cloud at $\sim10^{18}$cm from the source.