Blazars are one class of jetted active galactic nuclei, with small viewing angle, thus the relativistic jet points almost directly to our line of sight (Urry and Padovani, 1995). Blazars are known for their for their variability at all frequencies with a dominant component of non-thermal emission. They can be classified as Flat Spectrum Radio Quasars (FSRQ) or BL Lac type, depending on the visible features in their optical spectrum. 3C 279 is an FSRQ at z = 0.536, and was among the first quasars discovered to emit gamma-rays via observations by the Compton Gamma-Ray Observatory (Hartman et al., 1992). In this proceeding, we present the preliminary results of a multiwavelength variability study on the source 3C 279.

Our multiwavelength datasets include data from different public databases as well as our own observations. The gamma-ray data was retrieved from the Fermi Science Support Center database¹, which was observed by the Fermi Large Area Telescope (Fermi/LAT, Abdo et al., 2009). The X-rays was observed by the Swift X-Ray Telescope (Swift/XRT, Stroh and Falcone, 2013), 1mm observations were taken with the submillimeter Array² (SMA, Gurwell et al., 2007), Near Infrared photometry from the Observatorio Astrofísico Guillermo Haro (OAGH) and the SMARTS project³ (Bonning et al., 2012); optical V Band from the Steward Observatory⁴ (Smith et al., 2009) and SMARTS; optical spectra from OAGH (Patiño-Álvarez et al., 2013) and the Steward Observatory; and polarization spectra from the Steward Observatory as well. Details on data reduction can be found in the references given.

Based on the behavior of the gamma-rays with respect to the UV, optical and NIR, we separated the entire time range into three different periods: A flaring period in multiple bands, with counterparts in gamma-rays; a flaring period in multiple bands with no counterparts in gamma-rays; and another flaring period in multiple bands with apparent counterparts in gamma-rays. We also performed cross-correlation analysis on these activity periods of the light curves.

Period A ranges from JD₂₄₅ = 4, 650−5, 850 (see Figure 1 left panel). During this period, we observed multiple flares in the gamma-ray emission, as well as counterparts in the optical (V-band), UV continuum, and NIR emission (J-, H- and K-bands). In the 1 mm light curve we observed a response to each of these flares, however, the amplitude of the 1 mm flares is not as high as in the other wavelengths.

Period B ranges from JD₂₄₅ = 5, 850−6, 400 (see Figure 2). During this time period, we observed multiple flares in the optical V-band, with clear counterparts in the UV spectral continuum and NIR bands. We also observed an increase in the 1 mm emission responding to each of these flares. The highest levels of 1 mm emission over the entire time-frame of our observations occur during this activity period. There are increases in polarization degree coincident with these flares; this might indicate that these flares have a non-thermal origin. However, there are no counterparts to any of these flares in the gamma-rays.

Period C ranges from JD₂₄₅ = 6,400 − 6,850 (see Figure 1 right panel). During this time period, we observed the highest levels of gamma-ray emission in our time-frame of study. At the start of this time period we observe a very intense flare in the gamma-rays with a clear counterpart in the 1 mm emission, and high levels of degree of polarization, however, we do not see any response in the wavelength range from UV to NIR.

In order to discern if the emission at different wavelengths are correlated, we applied Cross-Correlation analysis, by using three different methods: The Interpolated Cross-Correlation Function (ICCF, Gaskell and Sparke, 1986), the Discrete Cross-Correlation Function (DCCF, Edelson and Krolik, 1988), and the Z-Transformed Discrete Correlation Function (ZDCF, Alexander, 1997). The significance was calculated via Montecarlo simulations, and a correlation is only considered as significant if the signal is above 3-sigma, and we only state a delay when there is not more than one peak in the cross-correlation function.

With the results from the cross-correlation analysis, we have identified the simultaneity (|Δt| < 1 day) of the UV λ3000 Å continuum emission, the optical V Band, and the NIR J, H, and K bands. This correlation allows us to infer that the emissions from the middle UV range to the NIR are co-spatial. We report the finding of a significant correlation between the V Band and 1mm emission in our entire observation time range. By interpolating the V Band observations to the times of the 1mm observations, we obtain a Spearman correlation coefficient of 0.65, and a probability of obtaining this correlation by chance of P ≪ 0.01. This strongly suggests that the optical V Band emission should be dominated by non-thermal emission from the jet. These results also imply that the emission from the middle UV range to the NIR is dominated by synchrotron emission.

Figure 1 (left panel) shows the light curves for Period A, which is noteworthy because we have a response in the gamma-rays every time we have a flare or flux increase in the other bands. The cross-correlation analysis between the UV continuum and the gamma-rays shows a delay of −0.7 ± 5.0 days (consistent with zero delay), implying that the emission regions are co-spatial. This, added to the low activity in the X-rays (which come mainly from the inner accretion disk and hot corona), strongly suggests that the dominant gamma-ray emission mechanism during this activity period is Synchrotron Self-Compton.

We also show in Figure 1 (right panel) the light curves for Period C. This period comes after a quiescent state in the gamma-rays (see Figure 2, left panel), and is noteworthy for having the brightest gamma-ray flare observed in this source during our time-frame of observation. The cross-correlation analysis between the UV continuum and the gamma-rays shows a delay of 28.6 ± 4.8 days, indicating a separation between the UV continuum emission region and the gamma-ray emission region (in contrast to Period A). There is a delay between X-rays and gamma-rays of −0.1 ± 3.0 days (consistent with zero delay). Added to the delay obtained between the gamma-rays and UV continuum, points to the dominant gamma-ray emission mechanism being External Inverse Compton. We present for the first time observational evidence of a change with time in the dominant gamma-ray emission mechanism for a single source. This is an important result due to its implications for SED modeling of blazars and high-energy physics. The result could also imply that the gamma-ray emission zone is changing locations over time.

We report the finding of an anomalous activity period on 3C 279. In this period we have multiple flares in the λ3000 Å continuum with counterparts in the optical V and NIR bands. We also observe coincident increases in the polarized flux and optical polarization degree, as well as the highest flux levels of 1mm emission during our entire observational time range. However, there is no counterpart in the gamma-ray band to any of this activity. The light curves for this period are shown in Figure 2.

We propose that this anomalous behavior is caused by an increase in the gamma-ray opacity in the flaring region, due to an increase in the Lorentz factor in the flaring region. In order to test if this scenario is plausible, we performed analytical calculations of the cross sections for the inverse Compton scattering and the electron-positron pair production. By performing the full quantum mechanical calculations we were able to calculate the cross sections for the aforementioned processes as a function of the Lorentz factor. The results of these calculations can be seen in Figure 3. The full calculations will be available in Patiño-Álvarez et al. (submitted).

VP-Á analyzed multiwavelength data and spectra, spectroscopic observations, statistical analysis, the explanation for lack of gamma-ray emission, as well as the analytical model, and writing of the paper. SF analyzed spectroscopic and polarimetric data and writing of the paper. VC is the group leader, establishment of scientific objectives, general direction, and scientific discussion. EL-R participated in the polarimetric analysis as well as general reviewing and scientific discussion. JL-T discussion about statistical methods as well as general reviewing and discussion. ES general reviewing and scientific discussion. LC NIR observations. JV spectroscopic observations. AC general reviewing and scientific discussion.