3C 273 with NuSTAR: Unveiling the Active Galactic Nucleus

Kristin K. Madsen, Felix Fürst, Dominic J. Walton, Fiona A. Harrison, Krzysztof Nalewajko, David R. Ballantyne, Steve E. Boggs, Laura W. Brenneman, Finn Erland Christensen, William W. Craig, Andrew C. Fabian, Karl Forster, Brian W. Grefenstette, Matteo Guainazzi, Charles J. Hailey, Greg M. Madejski, Giorgio Matt, Daniel Stern, Roland Walter, William W. Zhang

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We present results from a 244 ks NuSTAR observation of 3C 273 obtained during a cross-calibration campaign with the Chandra, INTEGRAL, Suzaku, Swift, and XMM-Newton observatories. We show that the spectrum, when fit with a power-law model using data from all observatories except INTEGRAL over the 1-78 keV band, leaves significant residuals in the NuSTAR data between 30 and 78 keV. The NuSTAR 3-78 keV spectrum is well. described by an exponentially cutoff power law (Γ = 1.646± 0.006, Ecutoff = 202-34 +51 keV) with a weak reflection component from cold, dense material. There is also evidence for a weak (EW = 23 ± 11 eV) neutral iron line. We interpret these features as arising from coronal emission plus reflection off an accretion disk or distant material. Beyond 80 keV INTEGRAL data show clear excess flux relative to an extrapolation of the active galactic nucleus model fit to NuSTAR. This high-energy power. law is consistent with the presence of a beamed jet, which begins to dominate over emission from the inner accretion flow at 30-40 keV. Modeling the jet locally (in the NuSTAR + INTEGRAL band) as a power. law, we find that the coronal component is fit by ΓAGN = 1.638 ± 0.045, Ecutoff = 47 ± 15 keV, and jet photon index by Γjet = 1.05 ± 0.4. We also consider Fermi/LAT observations of 3C 273, and here the broadband spectrum of the jet can be described by a log-parabolic model, peaking at ∼ 2 MeV. Finally, we investigate the spectral variability in the NuSTAR band and find an inverse correlation between flux and Gamma.
Original languageEnglish
Article number14
JournalAstrophysical Journal
Issue number1
Number of pages11
Publication statusPublished - 2015


  • Quasars: individual (3C 273)
  • X-rays: individual (3C 273)


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