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The Bright $\gamma$-ray Flare of 3C 279 in June 2015: AGILE Detection and Multifrequency Follow-up Observations
C. Pittori, F. Lucarelli, F. Verrecchia, C. M. Raiteri, M. Villata, V. Vittorini, M. Tavani, S. Puccetti, M. Perri, I. Donnarumma, S. Vercellone, J. A. Acosta-Pulido, R. Bachev, E. Benitez, G. A. Borman, M. I. Carnerero, D. Carosati, W. P. Chen, Sh. A. Ehgamberdiev, A. Goded, et al (27)
Mar 21 2018 astro-ph.HE arXiv:1803.07529v1

@misc{1803.07529, author = {C.~Pittori and F.~Lucarelli and F.~Verrecchia and C.~M.~Raiteri and M.~Villata and V.~Vittorini and M.~Tavani and S.~Puccetti and M.~Perri and I.~Donnarumma and S.~Vercellone and J.~A.~Acosta-Pulido and R.~Bachev and E.~Benitez and G.~A.~Borman and M.~I.~Carnerero and D.~Carosati and W.~P.~Chen and Sh.~A.~Ehgamberdiev and A.~Goded and T.~S.~Grishina and D.~Hiriart and H.~Y.~Hsiao and S.~G.~Jorstad and G.~N.~Kimeridze and E.~N.~Kopatskaya and O.~M.~Kurtanidze and S.~O.~Kurtanidze and V.~M.~Larionov and L.~V.~Larionova and A.~P.~Marscher and D.~O.~Mirzaqulov and D.~A.~Morozova and K.~Nilsson and M.~R.~Samal and L.~A.~Sigua and B.~Spassov and A.~Strigachev and L.O.~Takalo and L.~A.~Antonelli and A.~Bulgarelli and P.~Cattaneo and S.~Colafrancesco and P.~Giommi and F.~Longo and A.~Morselli and F.~Paoletti}, title = {{T}he {B}right $\gamma$-ray {F}lare of 3{C} 279 in {J}une 2015: {AGILE} {D}etection and {M}ultifrequency {F}ollow-up {O}bservations}, year = {2018}, eprint = {1803.07529}, note = {arXiv:1803.07529v1} }
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We report the AGILE detection and the results of the multifrequency follow-up observations of a bright $\gamma$-ray flare of the blazar 3C 279 in June 2015. We use AGILE-GRID and Fermi-LAT $\gamma$-ray data, together with Swift-XRT, Swift-UVOT, and ground-based GASP-WEBT optical observations, including polarization information, to study the source variability and the overall spectral energy distribution during the $\gamma$-ray flare. The $\gamma$-ray flaring data, compared with as yet unpublished simultaneous optical data which allow to set constraints on the big blue bump disk luminosity, show very high Compton dominance values of $\sim 100$, with a ratio of $\gamma$-ray to optical emission rising by a factor of three in a few hours. The multi-wavelength behavior of the source during the flare challenges one-zone leptonic theoretical models. The new observations during the June 2015 flare are also compared with already published data and non-simultaneous historical 3C 279 archival data.
Exceptional outburst of the blazar CTA 102 in 2012: The GASP-WEBT campaign and its extension
V.M. Larionov, M. Villata, C.M. Raiteri, S.G. Jorstad, A.P. Marscher, I. Agudo, P.S. Smith, J.A. Acosta-Pulido, M.J. Arévalo, A.A. Arkharov, R. Bachev, D.A. Blinov, G. Borisov, G.A. Borman, V. Bozhilov, A. Bueno, M.I. Carnerero, D. Carosati, C. Casadio, W.P. Chen, et al (32)
Jun 28 2016 astro-ph.HE astro-ph.CO arXiv:1606.07836v1

@misc{1606.07836, author = {V.M.~Larionov and M.~Villata and C.M.~Raiteri and S.G.~Jorstad and A.P.~Marscher and I.~Agudo and P.S.~Smith and J.A.~Acosta-Pulido and M.J.~Arévalo and A.A.~Arkharov and R.~Bachev and D.A.~Blinov and G.~Borisov and G.A.~Borman and V.~Bozhilov and A.~Bueno and M.I.~Carnerero and D.~Carosati and C.~Casadio and W.P.~Chen and D.P.~Clemens and A.~Di Paola and Sh.A.~Ehgamberdiev and J.L.~Gómez and P.A González-Morales and A.~Griñón-Marín and T.S.~Grishina and V.A.~Hagen-Thorn and S.~Ibryamov and R.~Itoh and E.N.~Kopatskaya and E.~Koptelova and C.~Lázaro and E.G.~Larionova and L.V.~Larionova and A.~Manilla-Robles and Y.~Metodieva and Yu.V.~Milanova and D.O.~Mirzaqulov and S.N.~Molina and D.A.~Morozova and S.V.~Nazarov and E.~Ovcharov and S.~Peneva and J.A.~Ros and A.C.~Sadun and S.S.~Savchenko and E.~Semkov and S.G.~Sergeev and A.~Strigachev and Yu.V.~Troitskaya and I.S.~Troitsky}, title = {{E}xceptional outburst of the blazar {CTA} 102 in 2012: {T}he {GASP}-{WEBT} campaign and its extension}, year = {2016}, eprint = {1606.07836}, note = {arXiv:1606.07836v1} }
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After several years of quiescence, the blazar CTA 102 underwent an exceptional outburst in 2012 September-October. The flare was tracked from gamma-ray to near-infrared frequencies, including Fermi and Swift data as well as photometric and polarimetric data from several observatories. An intensive GASP-WEBT collaboration campaign in optical and NIR bands, with an addition of previously unpublished archival data and extension through fall 2015, allows comparison of this outburst with the previous activity period of this blazar in 2004-2005. We find remarkable similarity between the optical and gamma-ray behaviour of CTA 102 during the outburst, with a time lag between the two light curves of ~1 hour, indicative of co-spatiality of the optical and gamma-ray emission regions. The relation between the gamma-ray and optical fluxes is consistent with the SSC mechanism, with a quadratic dependence of the SSC gamma-ray flux on the synchrotron optical flux evident in the post-outburst stage. However, the gamma-ray/optical relationship is linear during the outburst; we attribute this to changes in the Doppler factor. A strong harder-when-brighter spectral dependence is seen both the in gamma-ray and optical non-thermal emission. This hardening can be explained by convexity of the UV-NIR spectrum that moves to higher frequencies owing to an increased Doppler shift as the viewing angle decreases during the outburst stage. The overall pattern of Stokes parameter variations agrees with a model of a radiating blob or shock wave that moves along a helical path down the jet.
The awakening of BL Lacertae: observations by Fermi, Swift, and the GASP-WEBT
C. M. Raiteri, M. Villata, F. D'Ammando, V. M. Larionov, M. A. Gurwell, D. O. Mirzaqulov, P. S. Smith, for, GASP-WEBT collaboration
Sep 06 2013 astro-ph.HE astro-ph.CO arXiv:1309.1282v1

@misc{1309.1282, author = {C.~M.~Raiteri and M.~Villata and F.~D'Ammando and V.~M.~Larionov and M.~A.~Gurwell and D.~O.~Mirzaqulov and P.~S.~Smith and for and GASP-WEBT collaboration}, title = {{T}he awakening of {BL} {L}acertae: observations by {F}ermi, {S}wift, and the {GASP}-{WEBT}}, year = {2013}, eprint = {1309.1282}, note = {arXiv:1309.1282v1} }
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Since the launch of the Fermi satellite, BL Lacertae has been moderately active at gamma-rays and optical frequencies until May 2011, when the source started a series of strong flares. The exceptional optical sampling achieved by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT) in collaboration with the Steward Observatory allows us to perform a detailed comparison with the daily gamma-ray observations by Fermi. Discrete correlation analysis between the optical and gamma-ray emission reveals correlation with a time lag of 0 +- 1 d, which suggests cospatiality of the corresponding jet emitting regions. A better definition of the time lag is hindered by the daily gaps in the sampling of the extremely fast flux variations. In general, optical flares present more structure and develop on longer time scales than corresponding gamma-ray flares. Observations at X-rays and at millimetre wavelengths reveal a common trend, which suggests that the region producing the mm and X-ray radiation is located downstream from the optical and gamma-ray-emitting zone in the jet. The mean optical degree of polarisation slightly decreases over the considered period and in general it is higher when the flux is lower. The optical electric vector polarisation angle (EVPA) shows a preferred orientation of about 15 deg, nearly aligned with the radio core EVPA and mean jet direction. Oscillations around it increase during the 2011-2012 outburst. We investigate the effects of a geometrical interpretation of the long-term flux variability on the polarisation. A helical magnetic field model predicts an evolution of the mean polarisation that is in reasonable agreement with the observations. These can be fully explained by introducing slight variations in the compression factor in a transverse shock waves model.
Variability of the blazar 4C 38.41 (B3 1633+382) from GHz frequencies to GeV energies
C. M. Raiteri, M. Villata, P. S. Smith, V. M. Larionov, J. A. Acosta-Pulido, M. F. Aller, F. D'Ammando, M. A. Gurwell, S. G. Jorstad, M. Joshi, O. M. Kurtanidze, A. Lähteenmäki, D. O. Mirzaqulov, I. Agudo, H. D. Aller, M. J. Arévalo, A. A. Arkharov, U. Bach, E. Benítez, A. Berdyugin, et al (57)
Jul 18 2012 astro-ph.HE astro-ph.CO arXiv:1207.3979v1

@misc{1207.3979, author = {C.~M.~Raiteri and M.~Villata and P.~S.~Smith and V.~M.~Larionov and J.~A.~Acosta-Pulido and M.~F.~Aller and F.~D'Ammando and M.~A.~Gurwell and S.~G.~Jorstad and M.~Joshi and O.~M.~Kurtanidze and A.~Lähteenmäki and D.~O.~Mirzaqulov and I.~Agudo and H.~D.~Aller and M.~J.~Arévalo and A.~A.~Arkharov and U.~Bach and E.~Benítez and A.~Berdyugin and D.~A.~Blinov and K.~Blumenthal and C.~S.~Buemi and A.~Bueno and T.~M.~Carleton and M.~I.~Carnerero and D.~Carosati and C.~Casadio and W.~P.~Chen and A.~Di Paola and M.~Dolci and N.~V.~Efimova and Sh.~A.~Ehgamberdiev and J.~L.~Gómez and A.~I.~Gonzále and V.~A.~Hagen-Thorn and J.~Heidt and D.~Hiriart and Sh.~Holikov and T.~S.~Konstantinova and E.~N.~Kopatskaya and E.~Koptelova and S.~O.~Kurtanidze and E.~G.~Larionova and L.~V.~Larionova and J.~León-Tavares and P.~Leto and H.~C.~Lin and E.~Lindfors and A.~P.~Marscher and I.~M.~McHardy and S.~N.~Molina and D.~A.~Morozova and R.~Mujica and M.~G.~Nikolashvili and K.~Nilsson and E.~P.~Ovcharov and N.~Panwar and M.~Pasanen and I.~Puerto-Gimenez and R.~Reinthal and G.~M.~Richter and J.~A.~Ros and T.~Sakamoto and R.~D.~Schwartz and A.~Sillanpää and N.~Smith and L.~O.~Takalo and J.~Tammi and B.~Taylor and C.~Thum and M.~Tornikoski and C.~Trigilio and I.~S.~Troitsky and G.~Umana and A.~T.~Valcheva and A.~E.~Wehrle}, title = {{V}ariability of the blazar 4{C} 38.41 ({B}3 1633+382) from {GH}z frequencies to {G}e{V} energies}, year = {2012}, eprint = {1207.3979}, howpublished = {A&A 545, A48 (2012)}, note = {arXiv:1207.3979v1} }
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The quasar-type blazar 4C 38.41 (B3 1633+382) experienced a large outburst in 2011, which was detected throughout the entire electromagnetic spectrum. We present the results of low-energy multifrequency monitoring by the GASP project of the WEBT consortium and collaborators, as well as those of spectropolarimetric/spectrophotometric monitoring at the Steward Observatory. We also analyse high-energy observations of the Swift and Fermi satellites. In the optical-UV band, several results indicate that there is a contribution from a QSO-like emission component, in addition to both variable and polarised jet emission. The unpolarised emission component is likely thermal radiation from the accretion disc that dilutes the jet polarisation. We estimate its brightness to be R(QSO) ~ 17.85 - 18 and derive the intrinsic jet polarisation degree. We find no clear correlation between the optical and radio light curves, while the correlation between the optical and \gamma-ray flux apparently fades in time, likely because of an increasing optical to \gamma-ray flux ratio. As suggested for other blazars, the long-term variability of 4C 38.41 can be interpreted in terms of an inhomogeneous bent jet, where different emitting regions can change their alignment with respect to the line of sight, leading to variations in the Doppler factor \delta. Under the hypothesis that in the period 2008-2011 all the \gamma-ray and optical variability on a one-week timescale were due to changes in \delta, this would range between ~ 7 and ~ 21. If the variability were caused by changes in the viewing angle \theta only, then \theta would go from ~ 2.6 degr to ~ 5 degr. Variations in the viewing angle would also account for the dependence of the polarisation degree on the source brightness in the framework of a shock-in-jet model.

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