3C 273 with NuSTAR: Unveiling the AGN

We present results from a 244,ks $\mathit{\text{NuSTAR}}$ observation of 3C,273 obtained during a cross-calibration campaign with the $\mathit{\text{Chandra}}$, $\mathit{\text{INTEGRAL}}$, $\mathit{\text{Suzaku}}$, $\mathit{\text{Swift}}$, and $\mathit{\text{XMM-Newton}}$ observatories. We show that the spectrum, when fit with a power-law model using data from all observatories except $\mathit{\text{INTEGRAL}}$ over the 1–78,keV band, leaves significant residuals in the $\mathit{\text{NuSTAR}}$ data between 30–78,keV. The \nustar\ 3–78,keV spectrum is well-described by an exponentially cutoff power-law ($\mathrm{\Gamma }=1.646\pm 0.006$, E$$\mathrm{c}\mathrm{u}\mathrm{t}\mathrm{o}\mathrm{f}\mathrm{f}$ = 202{-34}^{+51}$,keV) with a weak reflection component from cold, dense material. There is also evidence for a weak ($EW=23\pm 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 $\mathit{\text{INTEGRAL}}$ data show clear excess flux relative to an extrapolation of the AGN 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 $\mathit{\text{NuSTAR}}$ + $\mathit{\text{INTEGRAL}}$ band) as a power-law, we find the coronal component is fit by ${\mathrm{\Gamma }}_{\mathrm{A}\mathrm{G}\mathrm{N}}=1.638\pm 0.045$, $E_{\mathrm{c}\mathrm{u}\mathrm{t}\mathrm{o}\mathrm{f}\mathrm{f}}=47\pm 15$,keV, and jet photon index by ${\mathrm{\Gamma }}_{\mathrm{j}\mathrm{e}\mathrm{t}}=1.05\pm 0.4$. We also consider $\mathit{\text{Fermi}}$/LAT observations of 3C,273 and here the broad-band spectrum of the jet can be described by a log-parabolic model, peaking at $\sim 2$,MeV. Finally, we investigate the spectral variability in the $\mathit{\text{NuSTAR}}$ band and find an inverse correlation between flux and $\mathrm{\Gamma }$.