NuSTAR observations of Mrk 766: distinguishing reflection from absorption

TL;DR

This study uses NuSTAR and XMM-Newton observations to distinguish between reflection and absorption models explaining the X-ray spectrum of Mrk 766, finding that a hybrid model best fits the data with less extreme parameters.

Contribution

It provides new constraints on the reflection and absorption scenarios in Mrk 766, demonstrating that a hybrid model explains the spectrum more realistically.

Findings

Pure reflection requires a high black hole spin and moderate inclination.

Pure partial covering demands extreme parameters like a very low cutoff energy.

Hybrid models yield more reasonable absorption parameters and relaxed reflection constraints.

Abstract

We present two new NuSTAR observations of the narrow line Seyfert 1 (NLS1) galaxy Mrk 766 and give constraints on the two scenarios previously proposed to explain its spectrum and that of other NLS1s: relativistic reflection and partial covering. The NuSTAR spectra show a strong hard (>15 keV) X-ray excess, while simultaneous soft X-ray coverage of one of the observations provided by XMM-Newton constrains the ionised absorption in the source. The pure reflection model requires a black hole of high spin ($a>0.92$) viewed at a moderate inclination ($i=46^{+1}_{-4}$ degrees). The pure partial covering model requires extreme parameters: the cut-off of the primary continuum is very low ($22^{+7}_{-5}$ keV) in one observation and the intrinsic X-ray emission must provide a large fraction (75%) of the bolometric luminosity. Allowing a hybrid model with both partial covering and reflection provides more reasonable absorption parameters and relaxes the constraints on reflection parameters. The fractional variability reduces around the iron K band and at high energies including the Compton hump, suggesting that the reflected emission is less variable than the continuum.