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Variability Observations of Blazar J0721+7120. A.G. Gorshkov 1 , V.K.Konnikova 1 M. Mingaliev 2 1 - Sternberg Astronomical Institute 2 - Special Astrophysical Observatory. Introduction.
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Variability Observationsof Blazar J0721+7120 A.G. Gorshkov1, V.K.Konnikova1 M. Mingaliev2 1 - Sternberg Astronomical Institute 2 - Special Astrophysical Observatory
Introduction • J0721+7120 (S5 0716+714) is from the bright sources (S5 GHz > 1Jy) sub-sample with flat spectra of the S5 catalogue. • J0721+7120 is identified with bright optical object (12m) with a continuum spectrum. • The host galaxy red shift is z=0.31 (?) • The optical spectrum is generated by jet focused practically along a line of sight (<2˚, VLBI-data) • From time delays of flares evolution -factor is derived: = 45-50; ≈ -2= 1 ˚ -1.5 ˚. • Amplitude of variability of this object one of the most among all types of AGNs and it is found out at all wavelengths from radio to gamma-rays. Characteristic variability scale is from ten of minutes (IDV) up to months.
Introduction • At radio frequencies variability is presented on all time scales from IDV (tens minutes, days) to the long-term (years). • In IDV cyclic components are observed; as well as in optic domain there can be cycles with the various characteristic times. • In long-term variability it is observed periodic component with the period about four years. • Duration of flares is 100-150 days. In a radio range there is delay of flares between different frequencies (on lower frequencies process develops later).
Observatuons Observations were done with the RATAN-600: • Simultaneously at 6 frequencies from 21.7 to 2.3 GHz; • 150 days (May 14 - October 15, 2009); • 57 days (March 05 - April 30, 2010). And with three telescopes of IAP (32-m dishes): • 4.85 GHz; • 13 daily sessions in 2009; • 14 daily sessions in 2010. The main purpose is to search for and analyze variability in wide range of time scales from several hours to days and more.
Light curves, 2009: filled circles - J0721+7120; open - circles – reference source. During the whole set the source was in a quiescent phase near to absolute minimum for all time of monitoring. Variability is visible simply by eye at all frequencies but 2.3 GHz. Variability looks like "anti-flares" or eclipses: there is fast enough flux decreasing and then returning to the former level with characteristic time close by recession time. During this set it is detected three eclipses.
To estimate “amplitude-frequency” characteristics the SF, ACF and CCF was used.
Results • SFs give significant variability at 4.85-21.7 GHz frequencies and no any at 2.3 GHz. • Average characteristic time of eclipses tacf=15days at 11.1, 7.7 and 4.85 GHz. Modulation indexes at these frequencies are m=5.7 %, 5.7 % and 5.2 %. • At 21.7 GHz characteristic time is not defined, m=7.3 %.
From the ACF maxima it is possible to get distances between eclipses: 38 days – between the first and the second; 60 days – between the second and the third. • These distances coincide with the distances taken from CCF between frequencies 11.1-7.7 GHz.
For the third eclipse it is possible to define a time delay in eclipse development: • 2 days - between 7.7 and 4.85 GHz; • 3 days - between 11.1 and 4.85 GHz; • Eclipse at lower frequency always takes place later.
Observations in 2010: 57 days March 05 - April30) These data are in sharp contrast with observations in 2009: • The minimum flux density exceeded maximum in 2009 (during flares); • The maximum flux density is comparable with an absolute maximum for all time of monitoring of this object; • Powerful outburst, comparable to the most powerful one of 2004 were detected.
Results τacfis approximately equal 20 days. The time delay between 11.1 and 7.7 GHz frequencies (from CCF) is about 6 days, the biggest one for all observed outbursts.
Results: spectrum of flare The flare is rising: α= 1.16 - for raw data; and α= 0.85 after removing a linear trend.
Conclusions • The outburst (2010) take place earlier for a one year than it was expected from estimations of precession (> 25 years). Probably the precession period is estimated incorrectly?! • The flare amplitude is comparable with the amplitude of powerful outbursts of 2004. • From difference of character of this flare one can suggests that this event is not connected with the precession period and it is due to the activity of the jet. To check this suggestion monitoring of J0721+7120 in 2011-2012 is desirable. • This flare was preceded by the considerable decreasing of flux density which is very usual for the most of active sources. • The nature of the eclipses observed in a minimum of luminosity in 2009 is not clear but is closely related to processes in jet. Unfortunately we did not yet finished to deal with IDV observations (IAP RAS) and Metsähovione.
