Raiteri, C. M.; Nicastro, F.; Stamerra, A.; Villata, M.; Larionov, V. M.; Blinov, D.; Acosta-Pulido, J. A.; Arévalo, M. J.; Arkharov, A. A.; Bachev, R.; Borman, G. A.; Carnerero, M. I.; Carosati, D.; Cecconi, M.; Chen, W.-P.; Damljanovic, G.; Di Paola, A.; Ehgamberdiev, Sh. A.; Frasca, A.; Giroletti, M.; González-Morales, P. A.; Griñon-Marín, A. B.; Grishina, T. S.; Huang, P.-C.; Ibryamov, S.; Klimanov, S. A.; Kopatskaya, E. N.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lähteenmäki, A.; Larionova, E. G.; Larionova, L. V.; Lázaro, C.; Leto, G.; Liodakis, I.; Martínez-Lombilla, C.; Mihov, B.; Mirzaqulov, D. O.; Mokrushina, A. A.; Moody, J. W.; Morozova, D. A.; Nazarov, S. V.; Nikolashvili, M. G.; Ohlert, J. M.; Panopoulou, G. V.; Pastor Yabar, A.; Pinna, F.; Protasio, C.; Rizzi, N.; Sadun, A. C.; Savchenko, S. S.; Semkov, E.; Sigua, L. A.; Slavcheva-Mihova, L.; Strigachev, A.; Tornikoski, M.; Troitskaya, Yu. V.; Troitsky, I. S.; Vasilyev, A. A.; Vera, R. J. C.; Vince, O.; Zanmar Sanchez, R.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 466, Issue 3, p.3762-3774
Description
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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