Context. Some intra-day variable, compact extra-galactic radio sources show brightness temperatures severely exceeding 10 12 K, the limit set by catastrophic inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation. The violation of the IC limit, actually possible under non-stationary conditions, would lead to IC avalanches in the soft-γ-ray energy band during transient periods. Aims. For the first time, broadband signatures of possible IC catastrophes were searched for in a prototypical source, S5 0716+71. Methods. A multifrequency observing campaign targetting S5 0716+71 was carried out during November 06−20, 2003. The observations, organized under the framework of the European Network for the Investigation of Galactic nuclei through Multifrequency Analysis (ENIGMA) together with a campaign by the Whole Earth Blazar Telescope (WEBT), involved a pointing by the soft-γ-ray satellite INTEGRAL, optical, near-infrared, sub-millimeter, millimeter, radio, as well as Very Long Baseline Array (VLBA) monitoring. Results. S5 0716+71 was very bright at radio frequencies and in a rather faint optical state (R = 14.17−13.64) during the INTEGRAL pointing; significant inter-day and low intra-day variability was recorded in the radio regime, while typical fast variability features were observed in the optical band. No obvious correlation was found between the radio and optical emission. The source was not detected by INTEGRAL, neither by the X-ray monitor JEM-X nor by the γ-ray imager ISGRI, but upper limits to the source emission in the 3−200 keV energy band were estimated. A brightness temperature T b > 2.1 × 10 14 K (violating the IC limit) was inferred from the variability observed in the radio regime, but no corresponding signatures of IC avalanches were recorded at higher energies. Conclusions. In the most plausible scenario of negligible contribution of the interstellar scintillation to the observed radio variability, the absence of the signatures of IC catastrophes provides either a lower limit δ > ∼ 8 to the Doppler factor affecting the radio emission or strong constraints for modelling of the Compton-catastrophe scenario in S5 0716+71.Key words. galaxies: active -galaxies: BL Lacertae objects: general -galaxies: BL Lacertae objects: individual: S5 0716+71 -galaxies: quasars: general -gamma-rays: observations -radiation mechanisms: non-thermal Partially based on observations obtained with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries:

Context. Theoretical predictions demonstrate that small (<0.1 µm) interstellar grains are mostly excluded from reaching the planetary system by electromagnetic interactions in the heliopause region and in the inner heliosphere. Bigger interstellar grains have been recorded in the planetary system by dust measurements on board Ulysses and other spacecraft. It was found that the interstellar dust flux is modulated by the interplanetary magnetic field. Aims. The objective of this study is to analyze the heliospheric filtering of the interstellar dust flow through the solar system and throughout the solar cycle. In the heliosphere the dynamics of interstellar dust is governed by the gravitational pull of the Sun, by the repulsion of solar radiation, and by the deflection caused by the interaction of the charged interstellar dust (ISD) grains with the interplanetary magnetic field. These interactions are described by the parameters of the radiation pressure constant β and the charge-to-mass ratio Q/m, which depend on the particle's size, physical properties, and composition. A previous paper studied the flow characteristics of ISD moving through the solar system were studied. In this follow-up paper, we focus on how the ISD size distribution varies during its passage through the solar system. Methods. In a parametric study of 70 different β and Q/m values, we calculated interstellar dust trajectories starting at the boundary of the heliosphere with starting times spread over a complete solar cycle of 22 years. Results. As a result we obtained the interstellar dust flux and dust speed for these times and positions and demonstrate the effects of the filtering on the dust size distributions. The size distribution of ISD observed at any time and at any position in the planetary system is strongly modified from when it entered the heliosphere. Peaks in relative flux of 10 times the original flux possibly depend on the grain size and place and time in the solar system. We did a detailed study of three cases of the flux and size distribution of interstellar grains reaching the planets Saturn, Jupiter, and the main-belt asteroid Ceres. These cases are used to get a first idea of what a dust detector or collector on a mission to these bodies might see of ISD.

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