Multiwavelength analysis of brightness variations of 3C~279: Probing the relativistic jet structure and its evolution

We studied the correlation between brightness and polarization variations in 3C~279 at different wavelengths, over time intervals long enough to cover the time lags due to opacity effects. We used these correlations together with VLBI images to constrain the radio and high energy source position.We made 7 mm radio continuum and $R$-band polarimetric observations of 3C~279 between 2009 and 2014. The radio observations were performed at the Itapetinga Radio Observatory, while the polarimetric data were obtained at Pico dos Dias Observatory, both in Brazil. We compared our observations with the $\gamma$-ray Fermi/LAT and $R$-band SMARTS light curves. We found a good correlation between 7~mm and $R$-band light curves, with a delay of $170 \pm 30$ days in radio, but no correlation with the $\gamma$ rays. However, a group of several $\gamma$-ray flares in April 2011 could be associated with the start of the 7 mm strong activity observed at the end of 2011.We also detected an increase in $R$-band polarization degree and rotation of the polarization angle simultaneous with these flares. Contemporaneous VLBI images at the same radio frequency show two new strong components close to the core, ejected in directions very different from that of the jet.The good correlation between radio and $R$-band variability suggests that their origin is synchrotron radiation. The lack of correlation with $\gamma$-rays produced by the Inverse Compton process on some occasions could be due to the lack of low energy photons in the jet direction or to absorption of the high energy photons by the broad line region clouds. The variability of the polarization parameters during flares can be easily explained by the combination of the jet polarization parameters and those of newly formed jet components.Comment: 11 pages, 6 figures, 2 tables. Accepted by A&

Centaurus A: The Nearest Blazar?

Abstract. Centaurus A (NGC5128), at a distance of 3.4 Mpc is the nearest Active Galaxy, classified as a low luminosity Fanaroff-Riley class I object. Although the central source is completely obscured at optical wavelengths, VLBI studies at radio frequencies show an unresolved core and an asymmetric jet at sub-parsec scales. Kinematical studies of the jet components show subluminal expansion velocities, which together with the jet-counterjet intensity ratio implies that the jet direction forms a large angle with the line of sight (50 o to 80 o ). The nuclear emission is highly variable at all wavelengths, from radio to γ-rays. Single dish radio observations showed that the stronger, long duration outbursts (months to years) present a correlation at radio and X-rays, although it is not clear whether the emission mechanism is synchrotron radiation at both frequencies or if the inverse Compton process dominates at high energies. Moreover, no information is available about the correlation between the emission at these two frequencies at shorter timescales (days and hours), due to the lack of short term monitoring at radio frequencies. In this work we report 43 GHz monitoring of Cantaurus A at the Itapetinga Radio Observatory during the last year, with daily resolution during a three-month period. We found very large variations (factor of two) within a few days, which puts Centaurus A in the blazar category. These variations were superimposed to a continuous rise in flux density that lasted until the end of 2003, when it started a fast decline. No apparent correlation with the All Sky Monitor (ASM/RXTE) data was found at these short timescales

Multiwavelength flaring activity of PKS 1510-089

Aims. In this work, we analyse the multiwavelength brightness variations and flaring activity of FSRQ PKS 1510-089, aiming to constrain the position of the emission sources. Methods. We report 7 mm (43 GHz) radio and R-band polarimetric observations of PKS 1510-089. The radio observations were performed at the Itapetinga Radio Observatory, while the polarimetric data were obtained at the Pico dos Dias Observatory. The 7 mm observations cover the period between 2011 and 2013, while the optical polarimetric observations were made between 2009 and 2012. Results. At 7 mm, we detected a correlation between four radio and γ-ray flares with a delay of about 54 days between them; the higher frequency counterpart occurred first. Using optical polarimetry, we detected a large variation in polarization angle (PA) within two days associated with the beginning of a γ-ray flare. Complementing our data with other data obtained in the literature, we show that PA presented rotations associated with the occurrence of flares. Conclusions. Our results can be explained by a shock-in-jet model, in which a new component is formed in the compact core producing an optical and/or γ-ray flare, propagates along the jet, and after some time becomes optically thin and is detected as a flare at radio frequencies. The variability in the polarimetric parameters can also be reproduced; we can explain large variation in both PA and polarization degree (PD), in only one of them, or in neither, depending on the differences in PA and PD between the jet and the new component

Optical Polarimetry and Radio Observations of PKS1510-089 between 2009 and 2013

The blazar PKS 1510-089 has shown intense activity at γ -rays in the recent years. In this work, we discussed the results of our 7 mm radio continuum and optical polarimetric monitoring between 2009 and 2013. In 2009, we detected a large rotation of the optical polarization angle that we attributed to the ejection of new polarized components. In 2011, after the occurrence of several γ -rays flares, the radio emission started to increase, reaching values never observed before. We interpreted this increase as the consequence of the superposition of several new components ejected during the γ -rays flares. A delay was measured between the maximum in the radio emission and the γ -ray flares, which favors models involving expanding components like the shock-in-jet models. Finally, we tried to understand the polarization angle variability behavior filling the gaps in our observations with published results of other polarimetric campaigns, and using the criterion of minimum variation in the polarization angle between successive observations to solve the 180° multiplicity