NuSTAR Reveals the Comptonizing Corona of the Broad-Line Radio Galaxy 3C 382

TL;DR

NuSTAR observations of 3C 382 reveal a thermal Comptonization-dominated X-ray continuum with coronal cooling behavior similar to Seyfert galaxies, distinct from jet-dominated sources, and show weak reflection features suggesting an outflowing corona.

Contribution

First detailed NuSTAR study confirming the thermal Comptonization nature of 3C 382's X-ray emission and its coronal properties, differentiating it from jet-dominated AGN.

Findings

Coronal plasma cooled from 330 keV to 231 keV between observations.

X-ray spectra fit well with thermal and anisotropic Comptonization models.

Weak reflection features suggest an outflowing corona and ionized inner disk.

Abstract

Broad-line radio galaxies (BLRGs) are active galactic nuclei that produce powerful, large-scale radio jets, but appear as Seyfert 1 galaxies in their optical spectra. In the X-ray band, BLRGs also appear like Seyfert galaxies, but with flatter spectra and weaker reflection features. One explanation for these properties is that the X-ray continuum is diluted by emission from the jet. Here, we present two NuSTAR observations of the BLRG 3C 382 that show clear evidence that the continuum of this source is dominated by thermal Comptonization, as in Seyfert 1 galaxies. The two observations were separated by over a year and found 3C 382 in different states separated by a factor of 1.7 in flux. The lower flux spectrum has a photon-index of $\Gamma=1.68^{+0.03}_{-0.02}$, while the photon-index of the higher flux spectrum is $\Gamma=1.78^{+0.02}_{-0.03}$. Thermal and anisotropic Comptonization models provide an excellent fit to both spectra and show that the coronal plasma cooled from $kT_e=330\pm 30$ keV in the low flux data to $231^{+50}_{-88}$ keV in the high flux observation. This cooling behavior is typical of Comptonizing corona in Seyfert galaxies and is distinct from the variations observed in jet-dominated sources. In the high flux observation, simultaneous Swift data are leveraged to obtain a broadband spectral energy distribution and indicates that the corona intercepts $\sim 10$% of the optical and ultraviolet emitting accretion disk. 3C 382 exhibits very weak reflection features, with no detectable relativistic Fe K$\alpha$ line, that may be best explained by an outflowing corona combined with an ionized inner accretion disk.