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Long duration gamma-ray bursts are commonly associated with the deaths of massive stars. Spectroscopic studies using the afterglow as a light source provide a unique opportunity to unveil the medium surrounding it, probing the densest region of their galaxies. This material is usually in a low ionization state and at large distances from the burst site, hence representing the normal interstellar medium in the galaxy. Here we present the case of GRB 090426 at , whose optical spectrum indicates an almost fully ionized medium together with a low column density of neutral hydrogen. For the first time, we also observe variations in the Ly absorption line. Photoionization modelling shows that we are probing material from the vicinity of the burst ( pc). The host galaxy is a complex of two luminous interacting galaxies, which might suggest that this burst could have occurred in an isolated star-forming region outside its host galaxy created in the interaction of the two galaxies. [ABSTRACT FROM AUTHOR]

We present numerical simulations investigating the interaction of active galactic nucleus jets with galaxy clusters, for the first time taking into account the dynamic nature of the cluster gas and detailed cluster physics. The simulations successfully reproduce the observed morphologies of radio sources in clusters. We find that cluster inhomogeneities and large-scale flows have a significant impact on the morphology of the radio source and cannot be ignored a priori when investigating radio source dynamics. Morphological comparison suggests that the gas in the centres of clusters like Virgo and Abell 4059 shows significant shear and/or rotation. We find that shear and rotation in the intracluster medium move large amounts of cold material back into the path of the jet, ensuring that subsequent jet outbursts encounter a sufficient column density of gas to couple with the inner cluster gas, thus alleviating the problem of evacuated channels discussed in the recent literature. The same effects redistribute the excess energy Δ E deposited by the jet, making the distribution of Δ E at late times consistent with being isotropic. [ABSTRACT FROM AUTHOR]