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Astron. Astrophys. 341, 487-490 (1999)

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3. Discussion

Postburst nebular emission has been predicted as a result of the impulsive release of relativistic particles in the nebulae surrounding SGRs (Tavani 1994).

The time delay [FORMULA]T between the soft gamma-ray bursts and the nebular emission depends on the geometry of the relativistic outflow. If we assume that the inner shock radio in N49 is 0.1" (Rothschild et al. 1994), at the distance of the LMC, this is [FORMULA] cm. According to Tavani (1994), and in case of a beamed outflow not aligned with the line of sight, [FORMULA]T is comparable to the propagation time [FORMULA]t [FORMULA] [FORMULA] 30 d, and the nebular emission is comparable with the synchrotron timescale of the schock emission. However, if the flow is considered to be isotropic, the onset of nebular emission follows the burst ([FORMULA]T [FORMULA] 0) with a duration comparable to [FORMULA]t ([FORMULA] 30 d).

The negative result presented in this paper might favour the existence of a beamed outflow in SGR 0525-66 that it is not aligned with the line of sight, although we do not know which is the fraction of the nebular high-energy emission that will be reprocessed into optical wavelenghts.

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© European Southern Observatory (ESO) 1999

Online publication: December 4, 1998
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