We present optical follow up observations of the long GRB 001007 between 6.14 hours and ~468 days after the event. An unusually bright optical afterglow (OA) was seen to decline following a steep power law decay with index α = -2.03 ± 0.11, possibly indicating a break in the light curve at t - t0 < 3.5 days, as found in other bursts. Upper limits imposed by the LOTIS alerting system 6.14 hours after the gamma ray event provide tentative (1.2σ) evidence for a break in the optical light curve. The spectral index β of the OA yields -1.24 ± 0.57. These values may be explained both by several fireball jet models and by the cannonball model. Fireball spherical expansion models are not favoured. Late epoch deep imaging revealed the presence of a complex host galaxy system, composed of at least two objects located 1.2 arcsec (1.7σ) and 1.9 arcsec (2.7σ) from the afterglow position. Based on observations collected: at the European Southern Observatory, in La Silla and Paranal (Chile), ESO Large Programmes 165.H-0464(G), 165.H-0464(I) and 265.D-5742(A), granted to the GRACE Team; with the Livermore Optical Transient Imaging System's 0.11 m telephoto lenses, at the Lawrence Livermore National Laboratory, in California (USA); with the Instituto de Astrofísica de Canarias's 0.82 m telescope, at the Observatorio del Teide, in the island of Tenerife (Spain); with the Danish 1.54 m telescope, at the European Southern Observatory, in La Silla (Chile); and with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos, of the Instituto de Astrofísica de Canarias.
The bright optical afterglow of the long GRB 001007
FRONTERA, Filippo;
2002
Abstract
We present optical follow up observations of the long GRB 001007 between 6.14 hours and ~468 days after the event. An unusually bright optical afterglow (OA) was seen to decline following a steep power law decay with index α = -2.03 ± 0.11, possibly indicating a break in the light curve at t - t0 < 3.5 days, as found in other bursts. Upper limits imposed by the LOTIS alerting system 6.14 hours after the gamma ray event provide tentative (1.2σ) evidence for a break in the optical light curve. The spectral index β of the OA yields -1.24 ± 0.57. These values may be explained both by several fireball jet models and by the cannonball model. Fireball spherical expansion models are not favoured. Late epoch deep imaging revealed the presence of a complex host galaxy system, composed of at least two objects located 1.2 arcsec (1.7σ) and 1.9 arcsec (2.7σ) from the afterglow position. Based on observations collected: at the European Southern Observatory, in La Silla and Paranal (Chile), ESO Large Programmes 165.H-0464(G), 165.H-0464(I) and 265.D-5742(A), granted to the GRACE Team; with the Livermore Optical Transient Imaging System's 0.11 m telephoto lenses, at the Lawrence Livermore National Laboratory, in California (USA); with the Instituto de Astrofísica de Canarias's 0.82 m telescope, at the Observatorio del Teide, in the island of Tenerife (Spain); with the Danish 1.54 m telescope, at the European Southern Observatory, in La Silla (Chile); and with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos, of the Instituto de Astrofísica de Canarias.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
