Multi-wavelength observations of the Blazar 4C +28.07

Abstract

The active galactic nucleus 4C +28.07 is a flat spectrum radio quasar, one of the brightest at $\gamma$-ray energies. We study its multi-wavelength emission by analysing $\sim12.3$ years of \textit{Fermi-LAT} data in the $\gamma$-ray band and \textit{Swift-XRT/UVOT} available data in X-ray and Optical-to-Ultraviolet bands. In the $\gamma$-ray band, five flaring periods have been detected, during which the flux dramatically increases by several times (>5) compared with its average quiescent phase. Quasi-simultaneously with the flaring times, the X-ray and UVOT data detected by \textit{Swift-XRT/UVOT} have also been analysed. In one of the brightest flare periods (Flare 5; observed on Oct 12, 2018) the $\gamma$-ray flux reached $(6.7\pm0.81)\times 10^{-6}$ photon/cm^2/s ($\sim31\times$ higher than the mean flux over 12.3 years) with detection significance of $\sigma=6.1$. The apparent $\gamma$-ray luminosity of this flaring corresponds to $3.6\times10^{49}$ erg/s (for a distance of 8.38 Gpc), one of the highest $\gamma$-ray luminosities observed for blazars. Flare 5 has an estimated $\sim2$ hours time block, which can be considered the average $\gamma$-ray variability time. The variability time constrains the $\gamma$-ray emitting region size to <9e14 cm, which is close to the black hole radius. The spectral energy distributions (SEDs) in the $\gamma$-ray band for the $\sim12.3$ years of data show an early cut-off at $\sim14$ GeV; beyond $\sim60$ GeV, however, the spectrum hardens and is detected up to $\sim316$ GeV. Similar spectral behaviour is also noticeable for the SEDs of flares, which can be linked to the photon absorption by the emitting region's internal and external narrow-band radiation fields. Considering the significance of the obtained results from 4C\,+28.07, we compared the parameters with 3C\,279 and M87, to motivate further studies.