Abstract
Variability on time scales δt < t is observed on numerous occasions in the afterglows of cosmic gamma-ray bursts (GRBs). It is well known that the radiation originating in an external shock produced by the interaction of an ultrarelativistic jet with the ambient interstellar medium should not contain such variability within the framework of simple models. The corresponding constraints were established by Ioka et al. (2005) and, in some instances, are inconsistent with observations. On the other hand, if the motion is not relativistic, then the rapid afterglow variability can be explained much more easily. Various estimates of the transition time to a nonrelativistic motion in a GRB source are discussed in this connection. It has been shown that this transition should occur on an observed time scale of ∼10 days. In the case of a higher density of the surrounding material, ∼102−104 cm−3, or a stellar wind with Ṁ ∼ 10−5−10−4 M ⊙ yr−1, the transition to a nonrelativistic motion can occur on a time scale of ∼1 day. Such densities may well be expected in star-forming regions and around massive Wolf-Rayet stars.
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Original Russian Text © R.A. Burenin, 2007, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2007, Vol. 33, No. 12, pp. 899–902.
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Burenin, R.A. On the variability of afterglows from cosmic gamma-ray bursts—the possibility of a transition to a nonrelativistic motion. Astron. Lett. 33, 804–806 (2007). https://doi.org/10.1134/S1063773707120031
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DOI: https://doi.org/10.1134/S1063773707120031