Mutiwavelength analysis of 3C 279 :Two scenarios to explain light-curves
𝐒𝐮𝐧𝐠𝐦𝐢𝐧 𝐘𝐨𝒐𝟏,𝟐 , 𝐇𝐨𝐧𝐠𝐣𝐮𝐧 𝐀𝐧𝟏 , 𝐒𝐚𝐧𝐠 − 𝐒𝐮𝐧𝐠 𝐋𝐞𝐞𝟐,𝟑 and iMOGABA team1

Department of Astronomy and Space Sciences, Chungbuk National University, Korea
2

Korea Astronomy and Space Science Institute, Daejeon, Korea
3

University of Science and Technology, Daejeon, Korea

yoo.9191.sm@gmail.com

ABSTRACT
Blazars are active galactic nuclei with relativistic jets aligned to Earth and bright in the entire electromagnetic wavebands. The broadband emission is believed to be
produced in the jets until now there is no complete picture of blazar behavior. Thus, multi-wavelength data may give us hints towards the mechanisms of the emission,
such as flaring, occurring within the jet, and so contemporaneous broadband observations are key to understanding blazar physics. 3C 279 is a very bright blazar andexhibits frequent gamma-ray flares. This source has shown long-term variability in radio band since 2010 and more recently explosive activities at gamma rays. We havemade contemporaneous radio observations of the source using KVN, and here we present our analysis results of the KVN radio data archival data in other bands, anddiscuss two scenarios that could describe the behavior of the light-curves in 3C 279.
1. Introduction
variability is one of properties often observed from blazars. While many of research has been
focused on short periods of change in the high-energy bands(e.g., 𝛾-ray), some blazars exhibit
long-term periods of variation in the radio bands(Dermer and Giebels. 2016, Hovatta et al,2008). The recent behavior of 3C 279 was a rare case among them in radio band(Hovatta et al,2008), and we would like to talk about the analysis results considered with two scenarios toaccount for this change in 3C 279. (1) A large flare drives the change of the light curve. (2) Theoverlap of the small flares results in changes in the light curve.
2. DataOwens Valley Radio Observatory (OVRO) is a 40m single-dish radio telescope with anobserving frequency of 15 GHz. Observation data monitoring over 1800 blazers are available
on the web at (www.astro.caltech.edu/ovroblazars/).
Korean VLBI Network (KVN) is a radio interferometer operated by Korea and consists of 21m
3 telescopes. Four frequency simultaneous observation is possible, and the observing
frequency is 22/43/86/129Ghz. The KVN single-dish observation, Monitoring of Gamma-ray
Bright AGNs (MOGABA) data (Kang et al , was used to compare interferometric MOGABA(iMOGABA) data, and OVRO and iMOGABA data were used for spectral analysis.

Figure 1. Light curve of 3C 279. MOGABA data was reported by Kang et al. 2015

3. Results and Analysis
3-1 First scenario : A large flare drives the change of the lightcurve• Large trends up to MJD 57750 correspond to decay in the evolution ofshock• Considering observing frequency, It is difficult to specify the peakfrequency within the observing frequency range.
• Comparison with other studies of the same method (Figure 3, bottom) :- Valtaoja et al. 1992 : -0.26±0.08- Hovatta et al. 2008 : -0.24- model prediction: -0.2
• There are flux difference between single-dish(MOGABA) and VLBI(iMOGABA) observation.
3-2 Second scenario : The overlap of the small flares results inchanges in the light curve.
Figure 2. Spectral evolution in the shock model• Twenty flares were decomposed using the OVRO data.
described by Valtaoja et al. 1992. The shape of the• Variation of the viewing angle due to precession can change Doppler shock spectrum, shown at three epochs, remains
boosting effect on the flux.
unchanged, but its turnover peak frequency moves
along the evolutionary track (solid line) through the- Flux increment by Flare1 : 1.39 Jy
growth, plateau, and decay stages. If a new shock- Flux increment by Flare6 : 13.42 Jyoccurs,
theturnover
frequency
canbeexpectedto• we estimate Bulk Lorentz factor(Γ) to be ~ 28 from the change in peakincrease rapidly and then decrease.

flux of flare 1 and flare 6 (9.65 times flux increase)
4.Discussion

Figure 3. (Top) The change in turnover frequency overtime. The red solid-line is the result of chi2 fitting fromMJD 56250 to 57750 and the slope is -0.0115 ± 0.0014.
Dashed-line is 15 GHz(OVRO), which corresponds tothe limit of the turnover frequency. (middle) Turnoverpeak flux changes over time. (bottom) Normalized
relative flux density against the normalized frequency.
This is to compare the predictions with the shock model(Valtaoja et al, 1992). As a result of linear fitting, theslope is -0.295 ± 0.061.

3C 279 is a highly variable object, and various efforts have been madeto explain the phenomenon : a) phenomena caused by precession (Qian2011, Abraham & Carrara 1998), b) interactions between interstellar
medium and jet (Homan et al. 2003), c) jet components conflicts
between them (Jorstad et al. 2017) and etc.
This study examine the possibilities of two scenarios to account forvariations in 3C279. If variation is dominated by one large flare, it willshow spectral changes through GROWTH-PLATEAU-DECAY by shockevolution (Valtaoja et al. 1992). The change in turnover frequency until
MJD 57750 may imply the DECAY phase in the shock model and theincrease in turnover frequency after MJD 57750 may be interpreted as aspectral change caused by a new shock (see Figure 2 (Top)). On theother hand, since the observing frequency range is 15 ~ 129 GHz, hence
it is difficult to trust the turnover frequency below 15 GHz. In addition, theflux difference between MOGABA (sigle-dish) and iMOGABA (VLBI)
Figure 4. When assuming the viewing angle change
implies the possibility of missing flux in VLBI observations. Fluxdue to precession from 2.1 to 0.54 degrees (Qian
difference may be caused by (1) filtering effect caused by few number of2011), we can estimate Bulk Lorentz factor(Γ) throughtelescope, (2) effects of pointing accuracy during four frequency Figure 3. Decomposed flaring in the OVRO light the flux enhancement between flare 1 and flare 6 (see3+𝛼 ) calculation,Figure3).
In
theDopplerfactor(𝛿curveusing
20
flares.
Thehorizontal
dashedline
simultaneous observation, and (3) effect of diffused flux in the area far
the quiescent level (= 10 Jy). As a result spectral index (𝛼) is taken to be 0.5 (Homan et al.
from radio core. If we try with MOGABA data instead of iMOGABA, the represents2003).
of 𝜒 2 fitting, 𝜒 2 / DOF = 813.36 / 246 = 3.31
turnover frequency range appears to be determined between 15 and 22
GHz during decay (see Figure 1).
To illustrate the second scenario, the OVRO data is decomposed by multiple flares to show the overlapped results of multiple flares. Although it is difficult to identify eachcomponent that causes flare in OVRO observations, it is assumed that the events occur in the radio core of the relativistic and dominate the change of the overall flux. The
Bulk Lorentz factor (Γ ~ 28), estimated by the change in viewing angle, explains why 3C 279 is a very bright and highly variable object in the space.