Multifrequency study of the gamma-ray flaring BL Lacertae object PKS 2233–148 in 2009–2012. Issue 2 (15th November 2018) - Pushkarev, A B
ABSTRACT: We study the jet physics of the BL Lacertae object PKS 2233−148, making use of the synergy of observational data sets in the radio and γ-ray energy domains. The four-epoch multifrequency (4–43 GHz) very-long-baseline array (VLBA) observations focused on the parsec-scale jet were triggered by a flare in γ-rays registered by Fermi -LAT on 2010 April 23. We also used 15-GHz data from the OVRO 40-m telescope and MOJAVE VLBA monitoring programs. The jet shape of the source is found to be conical on scales probed by the VLBA observations, setting a lower limit of about 0.1 on its unknown redshift. Nuclear opacity is dominated by synchrotron self-absorption, with a wavelength-dependent core shift of$r_{\rm{core\;[mas]}}\approx 0.1\lambda _{[\text{cm}]}$ mas co-aligned with the innermost jet direction. The turnover frequency of the synchrotron spectrum of the very-long-baseline interferometry core shifts towards lower frequencies as the flare propagates down the jet, and the speed of this propagation is significantly higher, about 1.2 mas yr −1, than results from traditional kinematics based on tracking bright jet features. We have found indications that the γ-ray production zone in the source is located at large distances, 10–20 pc, from a central engine, and could be associated with the stationary jet features. These findings favour synchrotron self-Compton, possibly in combination with external Compton scattering by infrared seed photons from a slow sheath of the jet, as the dominant high-energy emission mechanism of the source.