Fermi Gamma-ray Space Telescope

Spectacular Gamma-ray Variability in FSRQ 3C279 during Large Outbursts

M. Hayashida
G. M. Madejski, K. Asano, D. J. Thompson, on behalf of Fermi-LAT collaboration, K. Nalewajko, M. Sikora


Repeatedly, the Flat Spectrum Radio Quasar 3C 279 becomes one of the brightest gamma-ray blazars in the sky. Powerful outbursts producing gamma-ray fluxes higher than 1e-5 ph/cm2/s (>100 MeV) were observed in December 2013, April 2014, and June 2015. The December 2013 outburst showed an unusually hard power-law gamma-ray spectrum (index~1.7), and an asymmetric light curve profile with a few-hour time scale variability. This could be successfully explained using our second order Fermi acceleration model (Hayashida et al. 2015; Asano & Hayashida 2015). The outburst in June 2015 was even more powerful, with an integral flux above 100 MeV of 4e-5 ph/cm2/s, the historically highest even including the EGRET era. Concurrently, the soft X-ray flux increased to the highest level ever measured by Swift-XRT. The high flux prompted a Fermi-LAT target of opportunity observation. The increase in exposure and the very high flux state of the source allowed us to resolve the gamma-ray flux on shorter than orbital time scales. Our analysis of the LAT data revealed variability on the order of a few-minutes, which is the most rapid observed with Fermi-LAT for any extragalactic sources outside of gamma-ray bursts. ?In this contribution, we will present the observational results of these outbursts from 3C279, with a focus on a detailed analysis of the June 2015 outburst. We will also discuss the possible origin of the outbursts including the emission model based on the stochastic acceleration.