On the Nature of the High-Energy Rollover in 1H 0419-577

TL;DR

This study analyzes NuSTAR and Swift observations of the Seyfert galaxy 1H 0419-577, revealing an extreme high-energy cutoff likely due to a combination of thermal Comptonization and intrinsic continuum steepness, influenced by variable absorption.

Contribution

It provides the first detailed analysis of the high-energy rollover in 1H 0419-577, suggesting a complex origin involving both thermal Comptonization and intrinsic spectral steepening, with implications for accretion physics.

Findings

High-energy cutoff is among the most extreme observed in AGN.

The cutoff is likely due to thermal Comptonization with low coronal temperature.

Variable warm absorption influences spectral variability.

Abstract

A NuSTAR/Swift observation of the luminous Seyfert 1 galaxy 1H 0419-577 taken during 2015 reveals one of the most extreme high energy cut-offs observed to date from an AGN - an origin due to thermal Comptonization would imply a remarkably low coronal temperature $kT \sim 15$ keV. The low energy peak of the spectrum in the hard X-ray NuSTAR band, which peaks before the expected onset of a Compton hump, rules out strong reflection as the origin of the hard excess in this AGN. We show the origin of the high energy rollover is likely due to a combination of both thermal Comptonization and an intrinsically steeper continuum, which is modified by absorption at lower energies. Furthermore, modeling the broadband XUV continuum shape as a colour-corrected accretion disc, requires the presence of a variable warm absorber to explain all flux and spectral states of the source, consistent with the previous work on this AGN. While absorber variations produce marked spectral variability in this AGN, consideration of all flux states allows us to isolate a colourless component of variability that may arise from changes in the inner accretion flow, typically at around $10 \, r_g$.