Optical spectropolarimetry of the GRB 020813 afterglow

Aaron J. Barth, Re'em Sari, Marshall H. Cohen, Robert W. Goodrich, Paul A. Price, Derek W. Fox, J. S. Bloom, Alicia M. Soderberg, S. R. Kulkarni

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Abstract

The optical afterglow of gamma-ray burst GRB 020813 was observed for 3 hr with the LRIS spectropolarimeter at the Keck I telescope, beginning 4.7 hr after the burst was detected by the HETE-2. The spectrum reveals numerous metal absorption lines that we identify with two systems at z = 1.223 and z = 1.255. We also detect an [O II] λ3727 emission line at z = 1.255, and we identify this galaxy as the likely host of the GRB. After a correction for Galactic interstellar polarization, the optical afterglow has a linear polarization of 1.8%-2.4% during 4.7-7.9 hr after the burst. A measurement of p = 0.80% ± 0.16% on the following night by Covino et al. demonstrates significant polarization variability over the next 14 hr. The lack of strong variability in the position angle of linear polarization indicates that the magnetic field in the jet is likely to be globally ordered rather than composed of a number of randomly oriented cells. Within the framework of afterglow models with collimated flows, the relatively low observed polarization suggests that the magnetic field components perpendicular and parallel to the shock front are only different by about 20%.

Original languageEnglish (US)
Pages (from-to)L47-L51
JournalAstrophysical Journal
Volume584
Issue number2 II
DOIs
StatePublished - Feb 20 2003

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afterglows
polarization
linear polarization
bursts
shock fronts
polarimeters
gamma ray bursts
magnetic fields
night
magnetic field
telescopes
galaxies
cells
metals
metal

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Barth, A. J., Sari, R., Cohen, M. H., Goodrich, R. W., Price, P. A., Fox, D. W., ... Kulkarni, S. R. (2003). Optical spectropolarimetry of the GRB 020813 afterglow. Astrophysical Journal, 584(2 II), L47-L51. https://doi.org/10.1086/373889
Barth, Aaron J. ; Sari, Re'em ; Cohen, Marshall H. ; Goodrich, Robert W. ; Price, Paul A. ; Fox, Derek W. ; Bloom, J. S. ; Soderberg, Alicia M. ; Kulkarni, S. R. / Optical spectropolarimetry of the GRB 020813 afterglow. In: Astrophysical Journal. 2003 ; Vol. 584, No. 2 II. pp. L47-L51.
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Barth, AJ, Sari, R, Cohen, MH, Goodrich, RW, Price, PA, Fox, DW, Bloom, JS, Soderberg, AM & Kulkarni, SR 2003, 'Optical spectropolarimetry of the GRB 020813 afterglow', Astrophysical Journal, vol. 584, no. 2 II, pp. L47-L51. https://doi.org/10.1086/373889

Optical spectropolarimetry of the GRB 020813 afterglow. / Barth, Aaron J.; Sari, Re'em; Cohen, Marshall H.; Goodrich, Robert W.; Price, Paul A.; Fox, Derek W.; Bloom, J. S.; Soderberg, Alicia M.; Kulkarni, S. R.

In: Astrophysical Journal, Vol. 584, No. 2 II, 20.02.2003, p. L47-L51.

Research output: Contribution to journalArticle

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N2 - The optical afterglow of gamma-ray burst GRB 020813 was observed for 3 hr with the LRIS spectropolarimeter at the Keck I telescope, beginning 4.7 hr after the burst was detected by the HETE-2. The spectrum reveals numerous metal absorption lines that we identify with two systems at z = 1.223 and z = 1.255. We also detect an [O II] λ3727 emission line at z = 1.255, and we identify this galaxy as the likely host of the GRB. After a correction for Galactic interstellar polarization, the optical afterglow has a linear polarization of 1.8%-2.4% during 4.7-7.9 hr after the burst. A measurement of p = 0.80% ± 0.16% on the following night by Covino et al. demonstrates significant polarization variability over the next 14 hr. The lack of strong variability in the position angle of linear polarization indicates that the magnetic field in the jet is likely to be globally ordered rather than composed of a number of randomly oriented cells. Within the framework of afterglow models with collimated flows, the relatively low observed polarization suggests that the magnetic field components perpendicular and parallel to the shock front are only different by about 20%.

AB - The optical afterglow of gamma-ray burst GRB 020813 was observed for 3 hr with the LRIS spectropolarimeter at the Keck I telescope, beginning 4.7 hr after the burst was detected by the HETE-2. The spectrum reveals numerous metal absorption lines that we identify with two systems at z = 1.223 and z = 1.255. We also detect an [O II] λ3727 emission line at z = 1.255, and we identify this galaxy as the likely host of the GRB. After a correction for Galactic interstellar polarization, the optical afterglow has a linear polarization of 1.8%-2.4% during 4.7-7.9 hr after the burst. A measurement of p = 0.80% ± 0.16% on the following night by Covino et al. demonstrates significant polarization variability over the next 14 hr. The lack of strong variability in the position angle of linear polarization indicates that the magnetic field in the jet is likely to be globally ordered rather than composed of a number of randomly oriented cells. Within the framework of afterglow models with collimated flows, the relatively low observed polarization suggests that the magnetic field components perpendicular and parallel to the shock front are only different by about 20%.

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Barth AJ, Sari R, Cohen MH, Goodrich RW, Price PA, Fox DW et al. Optical spectropolarimetry of the GRB 020813 afterglow. Astrophysical Journal. 2003 Feb 20;584(2 II):L47-L51. https://doi.org/10.1086/373889