The effect of magnetic fields on gamma-ray bursts inferred from
multi-wavelength observations of the burst of 23 January 1999
Galama, T. J., Briggs, M. S., Wijers, R. A. M. J., Vreeswijk, P. M., Rol, E.,
Band, D., van Paradijs, J., Kouveliotou, C., Preece, R. D., Bremer, M.,
Smith, I. A., Tilanus, R. P. J., de Bruyn, A. G., Strom, R. G.,
Pooley, G., Castro-Tirado, A. J., Tanvir, N., Robinson, C., Hurley, K.,
Heise, J., Telting, J., Rutten, R. G. M., Packham, C., Swaters, R.,
Davies, J. K., Fassia, A., Green, S. F., Foster, M. J., Sagar, R.,
Pandey, A. K., Nilakshi, Yadav, R. K. S., Ofek, E. O., Leibowitz, E.,
Ibbetson, P., Rhoads, J., Falco, E., Petry, C., Impey, C.,
Geballe, T. R., and Bhattacharya, D.
Gamma-ray bursts (GRBs) are thought to arise when an extremely relativistic
outflow of particles from a massive explosion (the nature of which is still
unclear) interacts with material surrounding the site of the explosion.
Observations of the evolving changes in emission at many wavelengths allow
us to investigate the origin of the photons, and so potentially determine
the nature of the explosion. Here we report the results of gamma-ray,
optical, infrared, submillimetre, millimetre and radio observations of the
burst GRB990123 and its afterglow.
Our interpretation of the data indicates that the initial and afterglow
emissions are associated with three distinct regions in the fireball.
The peak flux of the afterglow, one day after the burst, has a lower
frequency than observed for other bursts; this explains the short-lived
radio emission.
We suggest that the differences between bursts reflect variations in the
magnetic-field strength in the afterglow-emitting regions.
Status:
1999, Nature, 398, 394.
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