Rapid Variability of Blazar 3C 279 during Flaring States in 2013-2014 with Joint Fermi-LAT, NuSTAR, Swift, and Ground-Based Multiwavelength Observations
Abstract
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 10-5 photons cm-2 s-1, 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 }}}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}\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 {{Δ }}{{{Γ }}}{{X}}≃ 0.4 at ∼4 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≃ 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2015
- DOI:
- 10.1088/0004-637X/807/1/79
- arXiv:
- arXiv:1502.04699
- Bibcode:
- 2015ApJ...807...79H
- Keywords:
-
- galaxies: active;
- galaxies: jets;
- gamma rays: galaxies;
- quasars: individual: 3C 279;
- radiation mechanisms: non-thermal;
- X-rays: galaxies;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 17 pages, 10 figures, accepted for publication in The Astrophysical Journal