The high energy spectrum of 3C 273
We studied the high energy spectral variability of the bright quasar 3C 273 from ~1 keV up to ~10 GeV using data collected with RXTE-PCA, INTEGRAL and Fermi/LAT and compared them with radio data at 37 GHz collected at the Metsähovi Radio Observatory. Quasi-simultaneous broad band high energy spectra have been built at the epoch of γ ray flares and X-ray flares.
Both timing and spectral analysis suggest a two-component scenario, where the X-ray emission is likely dominated by a Seyfert-like component, while the γ ray emission is dominated by a blazar-like component originated in the relativistic jet.
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ABSTRACT
Aims. The high energy spectrum of 3C 273 is usually understood in terms of inverse-Compton emission in a relativistic leptonic jet. This model predicts variability patterns and delays that could be tested with simultaneous observations from the radio to the GeV range.
Methods. The instruments IBIS, SPI, JEM-X on board INTEGRAL, PCA on board RXTE, and LAT on board Fermi have enough sensitivity to follow the spectral variability of 3C 273 from the keV to the GeV. We looked for correlations between the different energy bands, including radio data at 37 GHz collected at the Metsähovi Radio Observatory and built quasi-simultaneous multiwavelength
spectra in the high energy domain when the source is flaring either in the X-rays or in the γ rays.
Results. Both temporal and spectral analysis suggest a two-component model to explain the complete high energy spectrum. X-ray emission is likely dominated by a Seyfert-like component while the γ-ray emission is dominated by a blazar-like component produced by the relativistic jet. The variability of the blazar-like component is discussed, comparing the spectral parameters in the two different spectral states. Changes of the electron Lorentz factor are found to be the most likely source of the observed variability.
3C 273 high energy spectra built at different epochs
3C 273 high energy multiwavelength spectra at different epochs fitted with the two component model: the cutoff powerlaw models the Seyfert like component at X-rays, the log-parabola models the blazar-like component at γ-rays. The blue line corresponds to the epoch of γ ray flares, the yellow line to the epoch of X-ray flares, the green line to CGRO data. The upper panel shows the SED, the best fit models (continuous lines) and the two components (dotted lines). The lower panel shows the residuals from the best fit models.
Credits: ISDC/V.Esposito
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