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

TL;DR

This study uses deep NuSTAR observations to analyze the spectral features of 1H0707-495 in a low-flux state, revealing the persistence of the Compton hump and flux-dependent shifts in the iron K alpha line, shedding light on relativistic effects near the black hole.

Contribution

First sensitive high-energy observations of 1H0707-495 above 10 keV in a low-flux state, linking spectral features to flux variations and relativistic effects.

Findings

Compton hump is still detectable in low-flux state.

Flux drop in iron K alpha band increases with flux.

The flux variation likely reflects changes in the relativistically broadened iron line.

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 K alpha band, a strong soft excess, and short timescale reverberation lags associated with these spectral features. In this paper, we present the first results of a deep 250 ks NuSTAR 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 K alpha 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 K alpha emission line. When the flux is low, the coronal source height is low, thus enhancing the most gravitationally redshifted emission.