Shao-Kun Li | Searcharxiv

arXiv2018

Optical and Gamma-Ray Variability Behaviors of 3C 454.3 from 2006 to 2011

We present our photometric monitoring of a flat spectrum radio quasar (FSRQ) 3C 454.3 at Yunnan observatories from 2006 to 2011. We find that the optical color of 3C 454.3 shows obvious redder-when-brighter trend, which reaches a saturation stage when the source is brighter than 15.15 mag at V band. We perform a simulation with multiple values of disk luminosity and spectral index to reproduce the magnitude-color diagram. The results show that the contamination caused by the disk radiation alone is difficult to produce the observed color variability. The variability properties during the outburst in December 2009 are also compared with $γ$-ray data derived from Fermi $γ$-ray space telescope. The flux variation of these two bands follow a linear relation with $F_γ \propto F_R^{1.14\pm0.07}$, which provides an observational evidence for external Compton process in 3C 454.3. Meanwhile, this flux correlation indicates that electron injection is the main mechanism for variability origin. We also explore the variation of the flux ratio $F_γ/F_R$ and the detailed structures in the lightcurves, and discuss some possible origins for the detailed variability behaviors.

astro-ph.HE↗

arXiv2016

Discovery of $γ$-ray emission from the radio-intermediate quasar III Zw 2: violent jet activity with intraday $γ$-ray variability

III Zw 2 is the prototype of radio-intermediate quasars. Although there is the evidence of possessing strong jet, significant $γ$-ray emission has not been reported before. In this work, we carry out a detailed analysis of the latest {\it Fermi}-LAT {\it Pass} 8 data. No significant $γ$-ray signal has been detected in the time-averaged 7-year {\it Fermi}-LAT data of III Zw 2, we however have identified two distinct $γ$-ray flares with isotropic luminosities of $\sim 10^{45}$ erg $\rm s^{-1}$. Multiwavelength data analysis (including also the optical photometric observations from Yunnan Observatories) are presented and the main finding is the simultaneous optical and $γ$-ray flares of III Zw 2 appearing in Nov. 2009. Violent $γ$-ray variability with doubling timescale of 2.5 hours was detected in another $γ$-ray flare in May 2010, for which the 3-hour $γ$-ray peak flux is $\sim 250$ times of the average flux in 7 years. Rather similar behaviors are observed in blazars and the blazar model can reasonably reproduce the spectral energy distribution of III Zw 2 in a wide energy range, strongly suggesting that its central engine resembles that of blazars. In view of its core which shares radio similarities with young radio sources together with the weak extended radio lobe emission, we suggest that III Zw 2 harbors a recurrent activity core and serves as a valuable target for investigating the fuelling and triggering of the activity in radio loud AGNs.

astro-ph.HE↗