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Published October 10, 2015 | Submitted + Published
Journal Article Open

3C 273 with NuSTAR: Unveiling the Active Galactic Nucleus


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, E_(cutoff) = 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 Γ_(AGN) = 1.638 ± 0.045, E_(cutoff) = 47 ± 15 keV, and jet photon index by Γ_(jet) = 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 Γ.

Additional Information

© 2015. The American Astronomical Society. Received 2015 June 16; accepted 2015 August 26; published 2015 October 5. We thank Chris Done for bringing to our attention the alternative interpretation of the jet as a two-component inverse Compton model, and the anonymous referee, whose remarks and corrections helped improve the quality of this paper. This work was supported under NASA Contract No. NNG08FD60C and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). Facilities: Fermi - Fermi Gamma-Ray Space Telescope (formerly GLAST), Chandra (CXO) - , INTEGRAL - International Gamma-Ray Astrophysics Laboratory satellite, NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, Suzaku - Suzaku (ASTRO-EII), Swift - Swift Gamma-Ray Burst Mission, and XMM - Newton X-Ray Multimirror Mission satellite.

Attached Files

Published - Craig_2015p14.pdf

Submitted - 1506.06182v2.pdf


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