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<jats:title>Abstract</jats:title> <jats:p>A comprehensive study of multifrequency correlations can shed light on the nature of variation for blazars. In this work, we collect the long-term radio, optical, and <jats:italic>γ</jats:italic>-ray light curves of PKS 1502+106. After performing the localized cross-correlation function analysis, we find that correlations between radio and <jats:italic>γ</jats:italic>-ray or <jats:italic>V</jats:italic> band are beyond the 3<jats:italic>σ</jats:italic> significance level. The lag of the <jats:italic>γ</jats:italic>-ray relative to 15 GHz is <jats:inline-formula> <jats:tex-math> <?CDATA $-{60}_{-10}^{+5}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab3e38ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> days, translating to a distance of <jats:inline-formula> <jats:tex-math> <?CDATA ${3.18}_{-0.27}^{+0.50}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab3e38ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> parsec (pc) between them. Within uncertainties, the locations of the <jats:italic>γ</jats:italic>-ray and optical emitting regions are roughly the same, and are away from the jet base within 1.2 pc. The derived magnetic field in optical and <jats:italic>γ</jats:italic>-ray emitting regions is about 0.36 G. The logarithm of <jats:italic>γ</jats:italic>-ray flux is significantly linearly correlated with that of <jats:italic>V</jats:italic>-band fluxes, which can be explained by the synchrotron self-Compton process, the external Compton processes, or the combination of them. We find a significant linear correlation in the plot of <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}\prod $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab3e38ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> (polarization degree) versus <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}\nu {F}_{\nu }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab3e38ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> at <jats:italic>V</jats:italic> band, and use the empirical relation Π ∼ sin<jats:sup> <jats:italic>n</jats:italic> </jats:sup> <jats:italic>θ</jats:italic>′ (<jats:italic>θ</jats:italic>′ is the observing angle in the comoving frame blob) to explain it. The behaviors of color index (generally redder when brighter at the active state) and <jats:italic>γ</jats:italic>-ray spectral index (softer when brighter) could be well explained by the twisted jet model. These findings suggest that the curvature effect (mainly due to the change of the viewing angle) is dominant in the variation phenomena of fluxes, spectral indices, and polarization degrees for PKS 1502+106.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>After the identification of a candidate <jats:italic>γ</jats:italic>-ray transient in the error region of the binary black hole (BBH) merger GW150914 by the <jats:italic>Fermi</jats:italic> satellite, the question of whether BBH mergers can be associated with electromagnetic counterparts remains highly debated. Here, we present radio follow-up observations of GW170608, a BBH merger that occurred during the second observing run (O2) of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). Our radio follow-up focused on a specific field contained in the GW170608 sky localization area, where a candidate high-energy transient was detected by the <jats:italic>Fermi</jats:italic> Large Area Telescope (LAT). We make use of data collected at 1.4 GHz with the Karl G. Jansky Very Large Array (VLA), as well as with the VLA Low-band Ionosphere and Transient Experiment (VLITE). Our analysis is sensitive to potential radio afterglows with luminosity densities <jats:italic>L</jats:italic> <jats:sub>1.4GHz</jats:sub> ≳ 6 × 10<jats:sup>28</jats:sup> erg s<jats:sup>−1</jats:sup> Hz<jats:sup>−1</jats:sup>. In the most optimistic theoretical models, ≈20% of BBH events occurring in massive hosts could be associated with outflows as radio luminous as this. Although we find no evidence for the presence of a radio counterpart associated with the LAT candidate in the GW170608 error region, our analysis demonstrates the feasibility of future radio follow-up observations of well-localized BBHs. Comparing our radio upper limits with theoretical expectations for the radio afterglows potentially associated with jets launched in BBH mergers, we find that for jets of energy ≈10<jats:sup>49</jats:sup> erg seen on-axis, only jet angles <jats:italic>θ</jats:italic> <jats:sub>jet</jats:sub> ≳ 40° are compatible with the observations.</jats:p>