The customary picture of the fireball deceleration by an external medium neglects two physical agents in the problem that are important at radii R < 10 17 cm: a radiative precursor (the prompt GRB) and a relativistic front of free neutrons. The radiative precursor preaccelerates the medium

The problem of the interaction between the precessing mildly relativistic radio jets of SS 433 and an ambient medium has been often invoked in interpretations of the jets behaviour. The dynamical interaction could be responsible for disagreements between the kinematic model and observations

fragmentary but distinct boundary layer with a longitudinal magnetic field. The polarization distribution in the spine strongly supports shocked-jet models while that in the boundary layer suggests interaction with the surrounding medium. This behavior suggests a new way to understand the differing

Long gamma-ray bursts (GRBs) are likely associated with the collapse of massive stars, which produce dust and are born in dusty environments. Absorption and scattering of ultraviolet/X-ray photons from the prompt, optical flash and afterglow emission of the GRB produce dust echoes. We perform time-dependent calculations of these echoes, accounting for the evolution of the dust grain distribution due to selective grain destruction by the GRB radiation, and for off-axis beaming. We explore cloud configurations of differing density and size — the echo light curve and spectrum depend on the cloud radius, with larger clouds peaking at longer wavelengths. For a region ∼ 3 pc in size with density nH ∼ 10 3 cm −3, the echo spectrum peaks at ∼ 3.6 µm and ∼ 8.8 eV for thermal and scattered components, respectively. Dust echoes should be detectable with the Very Large Telescope up to z ∼ 0.1, IRAC onboard the Spitzer Space Telescope up to z ∼ 0.2, and NICMOS onboard the Hubble Space Telescope up to z ∼ 0.3. Furthermore, the shape of the echo light curve allows one to infer: the jet opening angle; the inclination of the jet axis with respect to the line of sight; the size of the dust-emitting region. For sources with symmetric, bipolar jets, dust echoes exhibit two bumps in the light curve, making them easily distinguishable from the rebrightening due to an underlying supernova. Subject headings: gamma-rays: bursts — radiative transfer — ISM: dust 1.

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-dimensional smoothed particle hydrodynamical simulations which suggest that this morphology may be due to the interaction of the propagating cooling jet with a non-homogeneous ambient medium. In regions where the ambient gas has an increasing density (and pressure) gradient, we find that it tends to compress the cold

of the ambient medium. For the wind case, we calculate analytically the frequencies of the normal modes which could modulate the early short-term variability of GRB afterglows. We find that perturbations in the double shock system could induce oscillatory fluctuations in the observed flux on short (down

Abstract—We present the line broadening and self-broadening coefficients of the water isotopologue HD 16 O and study their dependence on quantum numbers up to J = 50 for P-, Q-, and R-branches. Three calculation techniques have been used: the analytical model in the case of known quantum transition identification in normal modes; the JJ ' dependence in the case when only J and level symmetry are known, and the semiempirical calculation technique for 50 ≥ J> 15.The derived regularities for the broadening coefficients of water vapor lines allow accurate calculation of HD 16 O spectra including millions of weak lines from the VTT line list (Voronin, Tennyson, and Tolchenov). DOI: 10.1134/S1024856012010150

A fundamental computational problem in astrophysics is the motion of a cloud of gas forming a protostar in an ambient medium which is typically lower in density by a factor of < 10 12. The ambient medium can therefore be treated as