RAPID VARIABILITY OF BLAZAR 3C 279 DURING FLARING STATES IN 2013−2014 WITH JOINT<i>FERMI</i>-LAT,<i>NuSTAR</i>,<i>SWIFT</i>, AND GROUND-BASED MULTI-WAVELENGTH OBSERVATIONS

Abstract

Here we report the results of a multiband 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&gt;100 MeV) of 10&lt;sup&gt;-5&lt;/sup&gt; photons cm&lt;sup&gt;-2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;, and with a flux-doubling time scale as short as 2 hr. The γ-ray spectrum during one of the flares was very hard, with an index of Γ&lt;sub&gt;γ&lt;/sub&gt; =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&lt;sub&gt;γ&lt;/sub&gt;/L&lt;sub&gt;syn&lt;/sub&gt; &gt; 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 ΔΓ&lt;sub&gt;x&lt;/sub&gt; $\\simeq$ 0.4 at ~ keV. Modeling the broadband spectral energy distribution 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 $\\simeq$ 1, (3) total jet power significantly exceeding the accretion-disk luminosity L&lt;sub&gt;j&lt;/sub&gt;/L&lt;sub&gt;d&lt;/sub&gt; ≳ 10, and (4) extremely low jet magnetization with L&lt;sub&gt;B&lt;/sub&gt;/L&lt;sub&gt;j&lt;/sub&gt; ≲ 10&lt;sup&gt;-4&lt;/sup&gt;. In conclusion, 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.