IUCAA Preprints

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Subject: search.filters.subject.Radiation mechanisms

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    Gravity wave from mini-creation events
    (2015-01-13) Dasgupta, P.; Narlikar, J. V.
    This paper examines the possibility of testing the hypothesis recently proposed by some authors that, instead of the one-shot creation of the entire Universe in a big bang, creation of matter takes place in finite bursts at random in a Universe that is without a beginning and whose expansion on the large scale is as given by the steady state model. It is argued that if the creation events are anisotropic then they generate gravitational waves. Calculations are given to show that a laser interferometric detector of the UGO type would easily detect an event that generates -100-1000M0 .Further, the cosmological gravitational wave background generated by the minicreationevents is compared with the limits set by the analysis of the arrival time of pulses from millisecond pulsars. The existing data place severe constraints on the mass and anisotropies of the mini-creation events.
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    Detailed study of the GRB 030329 radio afterglow deep into the non-relativistic phase
    (2008-01) Horst, A. J. van der; Kamble, A.; Resmi, L.; et al.
    Radio afterglows ever, GRB 030329, at late times when the jet is non- relativistic. Aims. We determine the physical parameters of the blast wave and its surroundings, in particular the index of the electron energy distribution, the energy of the blast wave, and the density (structure) of the circumburst medium. We then compare our results with those from image size measurements. Methods. We observed the GRB030329 radio afterglow with the Westerbork Synthesis Radio Telescope and the Giant Metrewave Radio Telescope at frequencies from 325 MHz to 8.4 GHz, spanning a time range of 268-1128 days after the burst. We modeled all the available radio data and derived the physical parameters. Results. The index of the electron energy distribution is p = 2.1, the circumburst medium is homogeneous, and the transition to the non-relativistic phase happens at tNR ∼ 80 days. The energy of the blast wave and density of the surrounding medium are comparable to previous findings. Conclusions. Our findings indicate that the blast wave is roughly spherical at tNR, and they agree with the implications from the VLBI studies of image size evolution. It is not clear from the presented dataset whether we have seen emission from the counter jet or not. We predict that the Low Frequency Array will be able to observe the afterglow of GRB030329 and many other radio afterglows, constraining the physics of the blast wave during its non-relativistic phase even further