GRB 990510: linearly polarized radiation from a fireball

S. Covino; D. Lazzati; G. Ghisellini; P. Saracco; S. Campana; G. Chincarini; S. Di Serego; A. Cimatti; L. Vanzi; L. Pasquini; F. Haardt; G. L. Israel; L. Stella; M. Vietri; .

arXiv · astro-ph/9906319

GRB 990510: linearly polarized radiation from a fireball

S. Covino·D. Lazzati·G. Ghisellini·P. Saracco·S. Campana·G. Chincarini·S. Di Serego·A. Cimatti·L. Vanzi·L. Pasquini·F. Haardt·G. L. Israel·L. Stella·M. Vietri·.

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Abstract

Models for gamma-ray burst afterglows envisage an hyper-relativistic fireball that is decelerated in the ambient medium around the explosion site. This interaction produces a shock wave which amplifies the magnetic field and accelerates electrons to relativistic energies, setting the conditions for an efficient production of synchrotron photons. If produced in a region of large-scale ordered magnetic field, synchrotron radiation can be highly polarized. The optical transient associated with GRB 990510 was observed ~18.5 hr after the event and linear polarization in the R band was measured at a level of 1.7 +/- 0.2 %. This is the first detection of linear polarization in the optical afterglow of a gamma-ray burst. We exclude that this polarization is due to dust in the interstellar material, either in our Galaxy or in the host galaxy of the gamma-ray burst. These results provide important new evidence in favor of the synchrotron origin of the afterglow emission, and constrains the geometry of the fireball and/or magnetic field lines.

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S. Covino, D. Lazzati, G. Ghisellini, P. Saracco, S. Campana, G. Chincarini, S. Di Serego, A. Cimatti, L. Vanzi, L. Pasquini, F. Haardt, G. L. Israel, L. Stella, M. Vietri, .. 1999-06-18. GRB 990510: linearly polarized radiation from a fireball. https://arxiv.org/abs/astro-ph/9906319

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