The Broad-band X-ray Spectrum of IC 4329A from a Joint NuSTAR/Suzaku Observation

We have obtained a deep, simultaneous observation of the bright, nearby Seyfert galaxy IC 4329A with Suzaku and NuSTAR. Through a detailed spectral analysis, we are able to robustly separate the continuum, absorption and distant reflection components in the spectrum. The absorbing column is found to be modest at $N_H = 6 times 10^{21}$ cm$^2$, and does not introduce any significant curvature in the Fe K band. We are able to place a strong constraint on the presence of a broadened Fe K{alpha} line: $E = 6.46^{+0.08}_{-0.07}$ keV rest frame with ${sigma} = 0.33^{+0.08}_{-0.07}$ keV and $EW = 34^{+8}_{-7}$ eV, though we are not able to constrain any of the parameters of a relativistic reflection model. These results highlight the range in broad Fe K{alpha} line strengths observed in nearby, bright AGN (roughly an order of magnitude), and imply a corresponding range in the physical properties of the inner accretion disk in these sources. We have also updated our previously reported measurement of the high-energy cutoff of the hard X-ray emission using both observatories rather than just NuSTAR alone: $E_{cut} = 186 pm 14$ keV. This high-energy cutoff acts as a proxy for the temperature of the coronal electron plasma, enabling us to further separate this parameter from the optical depth of the plasma and to update our results for these parameters as well. We derive $kT = 50^{+6}_{-3}$ keV with ${tau} = 2.34^{+0.16}_{-0.11}$ using a spherical geometry, $kT = 61 pm 1$ keV with ${tau} = 0.68 pm 0.02$ for a slab geometry, with both having an equivalent goodness-of-fit.

Measuring Supermassive Black Hole Spins in Active Galactic Nuclei

Measuring the spins of supermassive black holes (SMBHs) in active galactic nuclei (AGN) can inform us about the relative role of gas accretion vs. mergers in recent epochs of the life of the host galaxy and its AGN. Recent advances in theory and observation have enabled spin measurements for a handful of SMBHs thus far, but this science is still very much in its infancy. Herein, I discuss how and why we seek to measure black hole spin in AGN, using recent results from long X-ray observing campaigns on three radio-quiet AGN (MCG-6-30-15, NGC 3783 and Fairall 9) to illustrate this process and its caveats. I then present our current knowledge of the distribution of SMBH spins in the local universe. I also address prospects for improving the accuracy, precision and quantity of these spin constraints in the next decade and beyond with instruments such as NuSTAR, Astro-H and a future generation large-area X-ray telescope.

NGC 5548: Lack of a Broad Fe K Line and Constraints on the Location of the Hard X-ray Source

We present an analysis of the co-added and individual 0.7-40 keV spectra from seven Suzaku observations of the Sy 1.5 galaxy NGC 5548 taken over a period of eight weeks. We conclude that the source has a moderately ionized, three-zone warm absorber, a power-law continuum, and exhibits contributions from cold, distant reflection. Relativistic reflection signatures are not significantly detected in the co-added data, and we place an upper limit on the equivalent width of a relativistically broad Fe K line at EW leq 26 eV at 90% confidence. Thus NGC 5548 can be labeled an weak type-1 AGN in terms of its observed inner disk reflection signatures, in contrast to sources with very broad, strong iron lines such as MCG-6-30-15, which are likely much fewer in number. We compare physical properties of NGC 5548 and MCG-6-30-15 that might explain this difference in their reflection properties. Though there is some evidence that NGC 5548 may harbor a truncated inner accretion disk, this evidence is inconclusive, so we also consider light bending of the hard X-ray continuum emission in order to explain the lack of relativistic reflection in our observation. If the absence of a broad Fe K line is interpreted in the light-bending context, we conclude that the source of the hard X-ray continuum lies at <100 gravitational radii. We note, however, that light-bending models must be expanded to include a broader range of physical parameter space in order to adequately explain the spectral and timing properties of average AGN, rather than just those with strong, broad iron lines.