RAPID VARIABILITY OF BLAZAR 3C 279 DURING FLARING STATES IN 2013−2014 WITH JOINTFERMI-LAT,NuSTAR,SWIFT, AND GROUND-BASED MULTI-WAVELENGTH OBSERVATIONS

Abstract

We report the results of a multi-band observing campaign on the famous blazar 3C 279 conducted during a phase of increased activity from 2013 December to 2014 April, including first observations of it with NuSTAR. The γ-ray emission of the source measured by Fermi-LAT showed multiple distinct flares reaching the highest flux level measured in this object since the beginning of the Fermi mission, with F(E > 100 MeV) of 10 −5 photons cm −2 s −1 , and with a flux doubling time scale as short as 2 hours. The γ-ray spectrum during one of the flares was very hard, with an index of Γ γ = 1.7 ± 0.1, which is rarely seen in flat spectrum radio quasars. The lack of concurrent optical variability implies a very high Compton dominance parameter L γ /L syn > 300. Two 1-day NuSTAR observations with accompanying Swift pointings were separated by 2 weeks, probing different levels of source activity. While the 0.5−70 keV X-ray spectrum obtained during the first pointing, and fitted jointly with Swift-XRT is well-described by a simple power law, the second joint observation showed an unusual spectral structure: the spectrum softens by ∆Γ X ≃ 0.4 at ∼ 4 keV. Modeling the broad-band SED during this flare with the standard synchrotron plus inverse Compton model requires: (1) the location of the γ-ray emitting region is comparable with the broad line region radius, (2) a very hard electron energy distribution index p ≃ 1, (3) total jet power significantly exceeding the accretion disk luminosity L j /L d 10, and (4) extremely low jet magnetization with L B /L j 10 −4 . We also find that single-zone models that match the observed γ-ray and optical spectra cannot satisfactorily explain the production of X-ray emission.

Scenarios for Ultrafast Gamma-Ray Variability in AGN

“…For 3C279, the lower limit on the jet luminosity is which is close to the Eddington limit. A similar estimate was obtained by Hayashida et al (2015).…”

“…The minumum detected variability time and gamma-ray luminosity were 4.5hr and 2 10 50 ergs −1 , respectively. Several similarly bright flares were detected form 3C279 in the period from 2013 December to 2014 April (Hayashida et al 2015). The GeV gamma-ray luminosity reached a level of and´-2 10 erg s 44 1 for 3C454.3 and 3C279, respectively.…”

“…This assumption also allows alarger (more "comfortable") size of theproduction region that isdemanded by the observed variability of radiation:  d D l c t var . These relations apply to all electromagnetic wavelengths, but they are crucial, first of all, for gamma-ray loud AGN, the apparent luminosities of which during strong flares, e.g., in 3C454.3 (Striani et al 2010;Abdo et al 2011) and 3C279 (Hayashida et al 2015), can achieve the level ofg 1 . Strong Doppler boosting is alsoneeded topreventsevere internal gamma-ray absorption, especially at VHE energies (see, e.g., Celotti et al 1998).…”

Kinetic Study of Radiation-Reaction-Limited Particle Acceleration During the Relaxation of Unstable Force-Free Equilibria

“…Rapid variability is also notably detected in many active galactic nuclei (AGNs). For example, the flat spectrum radio quasars (FSRQ) 3C 273 (e.g., Rani et al 2013) and 3C 279 (Hayashida et al 2015) produce GeV flares on hourly timescales; the radio galaxy IC310 (Aleksić et al 2014), the FSRQ PKS 1222+21 (Aleksić et al 2011), and several BL Lac objects, e.g., PKS 2155-304 (e.g., Aharonian et al 2007) and Markarian 501 (Albert et al 2007), are observed to flare in theTeV band with variability timescales of approximatelya few minutes. More strikingly, quite a few flares from blazars are found to be accompanied by large polarization angle swings in the optical band (Marscher et al 2008;Abdo et al 2010;Blinov et al 2015;Kiehlmann et al 2016), suggesting that the dissipation region has a coherent, strong magnetic field.…”

Formation of very hard electron and gamma-ray spectra of flat-spectrum radio quasars in the fast-cooling regime

“…Modeling by Hayashida et al (2015) with a broken power-law EED showed that a very hard electron spectrum with p ∼ 1 below γ ′ b ∼ 3000 is required to explain this very hard Fermi -LAT spectrum. In the slowcooling regime, such a hard emitting electron spectrum requires a very hard injection electron distribution.…”