The WEBT campaign on the BL Lac object PG 1553+113 in 2013. An analysis of the enigmatic synchrotron emission

Raiteri, C. M.; Stamerra, A.; Villata, M.; Larionov, V. M.; Acosta-Pulido, J. A.; Arévalo, M. J.; Arkharov, A. A.; Bachev, R.; Benítez, E.; Bozhilov, V. V.; Borman, G. A.; Buemi, C. S.; Calcidese, P.; Carnerero, M. I.; Carosati, D.; Chigladze, R. A.; Damljanovic, G.; Di Paola, A.; Doroshenko, V. T.; Efimova, N. V.; Ehgamberdiev, Sh. A.; Giroletti, M.; González-Morales, P. A.; Griñon-Marin, A. B.; Grishina, T. S.; Hiriart, D.; Ibryamov, S.; Klimanov, S. A.; Kopatskaya, E. N.; Kurtanidze, O. M.; Kurtanidze, S. O.; Kurtenkov, A. A.; Larionova, L. V.; Larionova, E. G.; Lázaro, C.; Lähteenmäki, A.; Leto, P.; Markovic, G.; Mirzaqulov, D. O.; Mokrushina, A. A.; Morozova, D. A.; Mújica, R.; Nazarov, S. V.; Nikolashvili, M. G.; Ohlert, J. M.; Ovcharov, E. P.; Paiano, S.; Pastor Yabar, A.; Prandini, E.; Ramakrishnan, V.; Sadun, A. C.; Semkov, E.; Sigua, L. A.; Strigachev, A.; Tammi, J.; Tornikoski, M.; Trigilio, C.; Troitskaya, Yu. V.; Troitsky, I. S.; Umana, G.; Velasco, S.; Vince, O.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 454, Issue 1, p.353-367

Advertised on:
11
2015
Number of authors
62
IAC number of authors
8
Citations
37
Refereed citations
36
Description
A multifrequency campaign on the BL Lac object PG 1553+113 was organized by the Whole Earth Blazar Telescope (WEBT) in 2013 April-August, involving 19 optical, two near-IR, and three radio telescopes. The aim was to study the source behaviour at low energies during and around the high-energy observations by the Major Atmospheric Gamma-ray Imaging Cherenkov telescopes in April-July. We also analyse the UV and X-ray data acquired by the Swift and XMM-Newton satellites in the same period. The WEBT and satellite observations allow us to detail the synchrotron emission bump in the source spectral energy distribution (SED). In the optical, we found a general bluer-when-brighter trend. The X-ray spectrum remained stable during 2013, but a comparison with previous observations suggests that it becomes harder when the X-ray flux increases. The long XMM-Newton exposure reveals a curved X-ray spectrum. In the SED, the XMM-Newton data show a hard near-UV spectrum, while Swift data display a softer shape that is confirmed by previous Hubble Space Telescope/Cosmic Origins Spectrograph and International Ultraviolet Explorer observations. Polynomial fits to the optical-X-ray SED show that the synchrotron peak likely lies in the 4-30 eV energy range, with a general shift towards higher frequencies for increasing X-ray brightness. However, the UV and X-ray spectra do not connect smoothly. Possible interpretations include: (i) orientation effects, (ii) additional absorption, (iii) multiple emission components, and (iv) a peculiar energy distribution of relativistic electrons. We discuss the first possibility in terms of an inhomogeneous helical jet model.
Related projects
Project Image
The Central PARSEC of Galaxies using High Spatial Resolution Techniques
PARSEC is a multi-wavelength investigation of the central PARSEC of the nearest galaxies. We work on black-hole accretion and its most energetic manifestations: jets and hot spots, and on its circumnuclear environment conditions for star formation. We resort to the highest available angular resolution observations from gamma-rays to the centimetre
Almudena
Prieto Escudero
Representación de la variable cataclísmica SS Cygni (Chris Moran)
Binary Stars
The study of binary stars is essential to stellar astrophysics. A large number of stars form and evolve within binary systems. Therefore, their study is fundamental to understand stellar and galactic evolution. Particularly relevant is that binary systems are still the best source of precise stellar mass and radius measurements. Research lines
Pablo
Rodríguez Gil
Project Image
Solar and Stellar Magnetism
Magnetic fields are at the base of star formation and stellar structure and evolution. When stars are born, magnetic fields brake the rotation during the collapse of the mollecular cloud. In the end of the life of a star, magnetic fields can play a key role in the form of the strong winds that lead to the last stages of stellar evolution. During
Tobías
Felipe García