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We report results of our polarimetric observations of comet 21P/Giacobini-Zinner made at phase angles, α ≈ 76-78°, between 10 and 17 of September, 2018, and compare them with previous measurements. We find significant variations in the polarimetric signals that appear consistent with those reported previously. These variations and subsequent modeling suggest that the particles in the coma are replenished within a period of approximately one day. This period is significantly shorter for highly absorbing carbonaceous particles than for non-absorbing Mg-rich silicate particles. Such a difference in the relative abundances of these components can lead to variations in the polarization response of the coma. The strong positive polarization in the subsolar direction suggests a large relative abundance of carbonaceous material, which may be an indicator of jet-type activity.

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Data of multiyear sun photometer measurements in the Asian part of Russia are used to analyze the issues regarding the modeling of annual and spectral behaviors of the atmospheric aerosol optical depth (AOD) based on separation of the contributions of fine and coarse aerosols. The specific features of the spatial distri bution and seasonal variations in AOD characteristics in different regions are discussed; and a three parameter model of annual behavior of spectral AOD in the range 0.34-4 µm for Western Siberia (Tomsk) is suggested.

Context. We present observations of the GRB 080319B afterglow at optical, mm, and radio frequencies between a few hours and 67 days after the burst. Aims. We attempt to understand the nature of this extraordinarily bright explosion based on the observed properties and its comparison with afterglow models. Methods. Our observations and other published multiwavelength data were used to reconstruct the light curves and spectral energy distributions of the burst afterglow. Results. Our results indicate that the observed features of the afterglow agrees equally well with the inter stellar matter and the stellar wind density profiles of the circumburst medium. In the case of both density profiles, the maximum synchrotron frequency ν m is below optical value and the cooling break frequency ν c is below X-rays, ∼10 4 s after the burst. The derived value of the Lorentz factor at the time of naked-eye brightness is also ∼300 for a corresponding blast-wave size of ∼10 18 cm. Conclusions. The numerical fit to the multiwavelength afterglow data constraints the values of physical parameters and the emission mechanism of the burst.