The Compton hump and variable blue wing in the extreme low-flux NuSTAR observations of 1H0707−495

Abstract

The narrow-line Seyfert I galaxy, 1H0707−495, has been well observed in the 0.3–10 keV band, revealing a dramatic drop in flux in the iron Kα band, a strong soft excess, and short time-scale reverberation lags associated with these spectral features. In this paper, we present the first results of a deep 250-ks NuSTAR (Nuclear Spectroscopic Telescope Array) observation of 1H0707−495, which includes the first sensitive observations above 10 keV. Even though the NuSTAR observations caught the source in an extreme low-flux state, the Compton hump is still significantly detected. NuSTAR, with its high effective area above 7 keV, clearly detects the drop in flux in the iron Kα band, and by comparing these observations with archival XMM–Newton observations, we find that the energy of this drop increases with increasing flux. We discuss possible explanations for this, the most likely of which is that the drop in flux is the blue wing of the relativistically broadened iron Kα emission line. When the flux is low, the coronal source height is low, thus enhancing the most gravitationally redshifted emission.