The NuSTAR view of the Seyfert Galaxy HE 0436-4717

TL;DR

This study analyzes multi-epoch NuSTAR observations of the Seyfert galaxy HE 0436-4717, revealing a stable primary continuum, a distant narrow Fe Kα line, and constraining the coronal properties with high-energy cut-off and temperature limits.

Contribution

First detailed spectral analysis of HE 0436-4717 with NuSTAR, providing constraints on coronal temperature, optical depth, and reflection features in a Seyfert galaxy.

Findings

Stable primary power law with photon index ~2.01

Constant narrow Fe Kα emission line indicating distant origin

Lower limit on high energy cut-off E_c > 280 keV

Abstract

We present the multi epoch spectral analysis of HE 0436-4717, a bright Seyfert 1 galaxy serendipitously observed by the high energy satellite NuSTAR four times between December 2014 and December 2015. The source flux shows modest variability within each pointing and among the four observations. Spectra are well modelled in terms of a weakly variable primary power law with constant photon index ($\Gamma$=2.01$\pm$0.08). A constant narrow \ion{Fe} K$\alpha$ emission line suggests that this feature has an origin far from the central black hole, while a broad relativistic component is not required by the data. The Compton reflection component is also constant in flux with a corresponding reflection fraction R=0.7$^{+0.2}_{-0.3}$. The iron abundance is compatible with being Solar (A$_{Fe}$=1.2$^{+1.4}_{-0.4}$), and a lower limit for the high energy cut-off E$_c$>280 keV is obtained. Adopting a self-consistent model accounting for a primary Comptonized continuum, we obtain a lower limit for the hot corona electron temperature kT$_e$>65 keV and a corresponding upper limit for the coronal optical depth of $\tau_e$<1.3. The results of the present analysis are consistent with the locus of local Seyfert galaxies in the kT$_e$-$\tau_e$ and temperature-compactness diagrams.