Near - infrared detection and optical follow - up of the GRB 990705 afterglow ⋆ , ⋆ ⋆

Optical and near-infrared observations of the GRB990705 error box were carried out with ESO telescopes at La Silla and Paranal in Chile and with the NOAO SPIREX 0.6-meter telescope in Antarctica. We detected the counterpart of this GRB in the near-infrared H band and optical V band. The power-law decline of the near-infrared lightcurve is rather steep with a decay index α ≃ 1.7 in the first hours, and a possible steepening after one day. Broadband spectral analysis of the optical/near-infrared afterglow suggests that this GRB took place in a high density environment. A deep optical image obtained at Antu (VLT-UT1) about 5 days after the GRB trigger shows at the position of the transient an extended object which might be the host galaxy of GRB990705. Send offprint requests to: Nicola Masetti, [email protected] ⋆ Based on observations collected at the European Southern Observatory, La Silla and Paranal, Chile ⋆⋆ Based on observations collected with NOAO facilities ⋆⋆⋆ Deceased on November 2, 1999