CORONAL PROPERTIES OF THE SEYFERT 1.9 GALAXY MCG-05-23-016 DETERMINED FROM HARD X-RAY SPECTROSCOPY WITHNuSTAR

Abstract

Measurements of the high-energy cut-off in the coronal continuum of active galactic nuclei have long been elusive for all but a small number of the brightest examples. We present a direct measurement of the cut-off energy in the nuclear continuum of the nearby Seyfert 1.9 galaxy MCG-05-23-016 with unprecedented precision. The high sensitivity of NuSTAR up to 79 keV allows us to clearly disentangle the spectral curvature of the primary continuum from that of its reflection component. Using a simple phenomenological model for the hard X-ray spectrum, we constrain the cut-off energy to 116 +6 −5 keV with 90% confidence. Testing for more complex models and nuisance parameters that could potentially influence the measurement, we find that the cut-off is detected robustly. We further use simple Comptonized plasma models to provide independent constraints for both the kinetic temperature of the electrons in the corona and its optical depth. At the 90% confidence level, we find kT e = 29 ± 2 keV and τ e = 1.23 ± 0.08 assuming a slab (disk-like) geometry, and kT e = 25 ± 2 keV and τ e = 3.5 ± 0.2 assuming a spherical geometry. Both geometries are found to fit the data equally well and their two principal physical parameters are correlated in both cases. With the optical depth in the τ e 1 regime, the data are pushing the currently available theoretical models of the Comptonized plasma to the limits of their validity. Since the spectral features and variability arising from the inner accretion disk have been observed previously in MCG-05-23-016, the inferred high optical depth implies that a spherical or disk-like corona cannot be homogeneous.

Evidence for Relativistic Disk Reflection in the Seyfert 1h Galaxy/ULIRG IRAS 05189–2524 Observed by NuSTAR and XMM-Newton

“…We note here that the cutoff energy is uncommonly low for an AGN, even compared with the lowest NuSTAR measurements (e.g., Baloković et al 2015;Ursini et al 2015;Tortosa et al 2016). This model generally has more uncertainty in the parameters; most notably, it places no constraint on the BH spin.…”

A Long Look at MCG-5-23-16 with NuSTAR. I. Relativistic Reflection and Coronal Properties

“…The higher ξ solution gives a better fit by D > W 30, corresponding to a significance of s >3.7 per observation. This solution is therefore preferred over that reported in Baloković et al (2015) for observation N2. Forcing the x~0 solution gives, in addition to a worse fit, lower cutoff energies but the correlations in Figure 7 hold.…”

Detection of the high-energy cut-off from the Seyfert 1.5 galaxy NGC 5273

“…Since high energy spectra (> 5 keV) are less affected by the absorption, they are most reliable for measuring photon power-law index as well as high energy cut-off (Nicastro et al 2000;Malizia et al 2014). NuSTAR spectra, with its unprecedented sensitivity at high energy (the detection limit in 10-30 keV is 1 × 10 −14 erg cm −2 s −1 ; Harrison et al (2013)), has provided strong constraints on the coronal properties as well as the cut-off energy of a few AGN (Brennman et al 2014;Fabian et al 2015;Balokovic et al 2015;Matt et al 2015).…”