Coffee talks
Friday 17/01/2020 @ 11:30, Sala riunioni quarto piano
Filippo D'ammando (INAF-IRA), "Blazar spectral variability as explained by a twisted inhomogeneous jet: the case of CTA 102"
Long-term multi-wavelength monitoring of blazars reveals that more intense periods of variability in brightness may occur when the jet is pointed more directly along our line of sight, thereby strengthening the geometric interpretation of long-term changes in brightness. The rich dataset and broad-band coverage provided from radio to gamma-rays by WEBT, OVRO, ALMA, Swift and Fermi during 2013-2017 make CTA 102 the best case to test the geometrical model as an explanation of the blazar spectral variability. In this talk I will show that the observed long-term trends of the flux and spectral variability in the optical-to-radio wavelengths are best explained by an inhomogeneous curved jet that undergoes changes in orientation over time. According to our model, the extreme optical outburst of 2016-2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. Unprecedented flaring activity was observed also in gamma-rays, with corresponding flux enhancements in the near-infrared, optical and UV bands and peaks observed at the same time. The gamma-ray flux variations show a strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This behaviour suggests that flux variations are mainly due to changes in the Doppler factor, in agreement with the geometrical model of a twisting inhomogeneous jet. The change of orientation in time of the emitting regions can be due to jet instabilities, precession, or orbital motions in a binary supermassive black hole system with important implications also for the gravitational-wave astronomy.