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EDP Sciences, Astronomy and Astrophysics Supplement Series, 3(138), p. 447-448

DOI: 10.1051/aas:1999302

American Astronomical Society, Astrophysical Journal, 1(523), p. 171-176, 1999

DOI: 10.1086/307740

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The X-ray, Optical and Infrared Counterpart to GRB 980703

Journal article published in 1999 by J. vanParadijs, P. M., Pm M. Vreeswijk, Vreeswijk Pm, T. J., Galama Tj, Pj J. Groot, Tj J. Galama, T. R., T. Koshut, Van Paradijs, A. N. Owens, Ramj A. M. J. Wijers, P. J., R. A. M. J. and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

We report on our X-ray, optical and infrared follow-up observations of GRB980703. A previously unknown X-ray source in the GRB error box displays a powerlaw decline with index alpha= -1.0,5(exp +0.24 sub -0.29), fairly consistent with the average optical/infrared decay index alpha = -1.61 plus or minus 0.12. We invoke host galaxy extinction to match the observed spectral slope with the slope expected from 'fireball' models. The hypothesis that between 1998 July 4.4 and 8.4 UT no spectral breaks are present in the infrared to X-ray spectral range is in good agreement with the observations. For these two epochs we obtain an extinction of A(sub v) = 1.50 +/- 0.11 (July 4.4) and A(sub v) = 0.85 +/- 0.26 (July 8.4). From the X-ray data we estimate the optical extinction to be A(sub v) = 20.2(+12.3/-7.3), inconsistent with the former value. Optical spectra we took confirm the redshift of z=0.966 found by Djorgovski et al. We compare the afterglow of GRB 980703 with that of GRB 970508 and find that the fraction of the energy in the magnetic field is much lower in the case of GRB 980703.