3C 273 with NuSTAR: Unveiling the AGN

الأصل · EN

We present results from a 244ks NuSTAR observation of 3C273 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--78keV band, leaves significant residuals in the NuSTAR data between 30--78keV. The 3--78keV spectrum is well-described by an exponentially cutoff power-law (Γ= 1.646 ± 0.006, Ecutoff = 202₋₃₄⁺⁵¹keV) 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 80keV INTEGRAL data show clear excess flux relative to an extrapolation of the AGN model fit to. 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 the coronal component is fit by ΓₐGN = 1.638 ± 0.045, Ecutoff = 47 ± 15keV, and jet photon index by Γⱼet = 1.05 ± 0.4. We also consider Fermi/LAT observations of 3C273 and here the broad-band spectrum of the jet can be described by a log-parabolic model, peaking at 2MeV. Finally, we investigate the spectral variability in the NuSTAR band and find an inverse correlation between flux and Γ.