Synchrotron emission from the blazar PG 1553+113. An analysis of its flux and polarization variability
C. M. RaiteriINAF, Osservatorio Astrofisico di Torino, via Osservatorio 20, I-10025 Pino Torinese, ItalyF. NicastroNational Institute for AstrophysicsA. StamerraASI Science Data Center, via del Politecnico s.n.c., I-00133 Roma, ItalyM. VillataINAF, Osservatorio Astrofisico di Torino, via Osservatorio 20, I-10025 Pino Torinese, ItalyV. M. LarionovAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaD. BlinovFoundation for Research and Technology – Hellas, IESL, Voutes, 71110 Heraklion, GreeceJ. A. Acosta‐PulidoDepartamento de Astrofisica, Universidad de La Laguna, La Laguna, E-38205 Tenerife, SpainM. J. ArévaloDepartamento de Astrofisica, Universidad de La Laguna, La Laguna, E-38205 Tenerife, SpainA. A. ArkharovPulkovo Observatory, 196140 St Petersburg, RussiaR. BachevInstitute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko shosse Blvd., 1784 Sofia, BulgariaG. A. BormanCrimean Astrophysical Observatory RAS, P/O Nauchny 298409, RussiaM. I. CarnereroINAF, Osservatorio Astrofisico di Torino, via Osservatorio 20, I-10025 Pino Torinese, ItalyD. CarosatiINAF, TNG Fundación Galileo Galilei, E-38712 La Palma, SpainM. CecconiINAF, TNG Fundación Galileo Galilei, E-38712 La Palma, SpainW.-P. ChenGraduate Institute of Astronomy, National Central University, 300 Jhongda Rd, Jhongli City, Taoyuan County 32001, Taiwan (R.O.C.)G. DamljanovićAstronomical Observatory, Volgina 7, 11060 Belgrade, SerbiaA. Di PaolaNational Institute for AstrophysicsSh. A. EhgamberdievUlugh Beg Astronomical Institute, Maidanak Observatory, 33 Astronomicheskaya str., Tashkent, 100052, UzbekistanA. FrascaINAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania, ItalyM. GirolettiINAF, Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna, ItalyP. A. González-MoralesDepartamento de Astrofisica, Universidad de La Laguna, La Laguna, E-38205 Tenerife, SpainAna Belén Griñón-MarínDepartamento de Astrofisica, Universidad de La Laguna, La Laguna, E-38205 Tenerife, SpainT. S. GrishinaAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaPi‐Chun HuangGraduate Institute of Astronomy, National Central University, 300 Jhongda Rd, Jhongli City, Taoyuan County 32001, Taiwan (R.O.C.)S. IbryamovInstitute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko shosse Blvd., 1784 Sofia, BulgariaS. A. KlimanovPulkovo Observatory, 196140 St Petersburg, RussiaE. N. KopatskayaAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaO. M. KurtanidzeAbastumani Observatory, Mt. Kanobili, 0301 Abastumani, GeorgiaS. O. KurtanidzeAbastumani Observatory, Mt. Kanobili, 0301 Abastumani, GeorgiaA. LähteenmäkiAalto University Metsähovi Radio Observatory, Metsähovintie 114, FI-02540 Kylmälä, FinlandЕ. Г. ЛарионоваAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaL. V. LarionovaAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaC. LázaroInstituto de Astrofisica de Canarias (IAC), La Laguna, E-38200 Tenerife, SpainG. LetoINAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania, ItalyIoannis LiodakisDepartment of Physics and ITCP, University of Crete, 71003 Heraklion, GreeceCristina Martínez-LombillaDepartamento de Astrofisica, Universidad de La Laguna, La Laguna, E-38205 Tenerife, SpainB. MihovInstitute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko shosse Blvd., 1784 Sofia, BulgariaD. O. MirzaqulovUlugh Beg Astronomical Institute, Maidanak Observatory, 33 Astronomicheskaya str., Tashkent, 100052, UzbekistanA. A. MokrushinaPulkovo Observatory, 196140 St Petersburg, RussiaJ. W. MoodyDepartment of Physics and Astronomy, Brigham Young University, Provo, UT 84602, USAD. A. MorozovaAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaS. V. NazarovCrimean Astrophysical Observatory RAS, P/O Nauchny 298409, RussiaM. G. NikolashviliAbastumani Observatory, Mt. Kanobili, 0301 Abastumani, GeorgiaJ. OhlertUniversity of Applied Sciences, Technische Hochschule Mittelhessen, D-61169 Friedberg, GermanyG. V. PanopoulouFoundation for Research and Technology – Hellas, IESL, Voutes, 71110 Heraklion, GreeceA. Pastor YabarDepartamento de Astrofisica, Universidad de La Laguna, La Laguna, E-38205 Tenerife, SpainFrancesca PinnaDepartamento de Astrofisica, Universidad de La Laguna, La Laguna, E-38205 Tenerife, SpainC. ProtasioDepartamento de Astrofisica, Universidad de La Laguna, La Laguna, E-38205 Tenerife, SpainN. RizziA. C. SadunDepartment of Physics, University of Colorado Denver, CO 80217-3364, USAС. С. СавченкоAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaE. SemkovInstitute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko shosse Blvd., 1784 Sofia, BulgariaL. A. SiguaAbastumani Observatory, Mt. Kanobili, 0301 Abastumani, GeorgiaL. Slavcheva‐MihovaInstitute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko shosse Blvd., 1784 Sofia, BulgariaA. StrigachevInstitute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko shosse Blvd., 1784 Sofia, BulgariaM. TornikoskiAalto University Metsähovi Radio Observatory, Metsähovintie 114, FI-02540 Kylmälä, FinlandYu. V. TroitskayaAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaI. S. TroitskyAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaA. A. VasilyevAstronomical Institute, St Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St Petersburg, RussiaR. J. C. VeraAalto University Metsähovi Radio Observatory, Metsähovintie 114, FI-02540 Kylmälä, FinlandO. VinceAstronomical Observatory, Volgina 7, 11060 Belgrade, SerbiaR. Zanmar SánchezINAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania, Italy
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Annotatsiya
In 2015 July 29-September 1, the satellite XMM-Newton pointed at the BL Lac object PG 1553+133 six times, collecting data for 218 h. During one of these epochs, simultaneous observations by the Swift satellite were requested to compare the results of the X-ray and optical-UV instruments. Optical, near-infrared and radio monitoring was carried out by the Whole Earth Blazar Telescope (WEBT) collaboration for the whole observing season. We here present the results of the analysis of all these data, together with an investigation of the source photometric and polarimetric behaviour over the last 3 yr. The 2015 EPIC spectra show slight curvature and the corresponding light curves display fast X-ray variability with a time-scale of the order of 1 h. In contrast to previous results, during the brightest X-ray states detected in 2015 the simple log-parabolic model that best fits the XMM-Newton data also reproduces reasonably well the whole synchrotron bump, suggesting a peak in the near-UV band. We found evidence of a wide rotation of the polarization angle in 2014, when the polarization degree was variable, but the flux remained almost constant. This is difficult to interpret with deterministic jet emission models, while it can be easily reproduced by assuming some turbulence of the magnetic field.
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