TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2612 SUBJECT: GRB 030329: Rebrightening of hyperluminal ejecta. DATE: 04/06/18 06:09:43 GMT FROM: Arnon Dar at Technion-Israel Inst. of Tech S. Dado [Technion], A. Dar [Technion] and A. De Rujula [CERN] report: Taylor, Frail, Berger and Kulkarni [1] reported the discovery of a second compact radio source in the afterglow of GRB 030329 at an angular distance of 0.28 +\- 0.05 mas from the main source on day 51.3 after burst, which was not resolved in their VLBI observations at other epochs. This separation is "hyperluminal": the relative mean sky-projected-velocity is > 19c. A transient strong rebrightening of the second radio source is consistent with the reported "jitter" first seen in observations of the optical afterglow that began on day 51.75 (GCN 2224 [2], GCN 2259 [3]). At that late time, the optical afterglow of GRB 030329/SN 2003dh is expected to be dominated by the supernova. The spectroscopic resolution of the afterglow into the individual contributions of the SN and GRB [2] indicates that the GRB contribution rebrightened by a factor 2 or more. An analogous rebrightening of the second radio source may explain why it was resolved only on day 51.3. The discovery [1] of a hyperluminal compact source may pin down the origin of GRBs [5]. We encourage prompt and follow-up VLBI observations of XRFs. In the cannonball model the source separation observed by Taylor et al. is the expected one [5], and both GRBs and XRFs are produced by hyperluminal plasmoids ejected in SN explosions. Relative to GRBs, XRFs are selectively viewed at closer distances, and at viewing angles typically 3 times larger [6]. This makes them very attractive targets for radio searches of the expected hyperluminal motions, in particular promptly after the burst. [1] astro-ph/0405300: G.B. Taylor, D.A. Frail, E. Berger, S. Kulkarni [2] GCN 2224: K.Z. Stanek, D.W. Latham, M.E. Everett [3] GCN 2259: K.Z. Stanek, D. Bersier, M. Calkins, D.L. Freedman, T. Spahr [4] astro-ph/0307435: T. Matheson et al. [5] astro-ph/0406325: Dado, A. Dar, A. De Rujula [6] astro-ph/0309294: S. Dado, A. Dar, A. De Rujula