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EnglishGRB080319B reached fifth optical magnitude during the burst prompt emission. Thanks to the Very Large Telescope (VLT)/Ultraviolet and Visual Echelle Spectrograph (UVES) rapid response mode, we observed its afterglow just 8m:30s after the gamma-ray burst (GRB) onset when the magnitude was R ~ 12. This allowed us to obtain the best signal-to-noise (S/N), high-resolution spectrum of a GRB afterglow ever (S/N per resolution element ~50). The spectrum is rich of absorption features belonging to the main system at z = 0.937, divided in at least six components spanning a total velocity range of 100 km s–1. The VLT/UVES observations caught the absorbing gas in a highly excited state, producing the strongest Fe II fine structure lines ever observed in a GRB. A few hours later, the optical depth of these lines was reduced by a factor of 4-20, and the optical/UV flux by a factor of ~60. This proves that the excitation of the observed fine structure lines is due to "pumping" by the GRB UV photons. A comparison of the observed ratio between the number of photons absorbed by the excited state and those in the Fe II ground state suggests that the six absorbers are ~2-6 kpc from the GRB site, with component I ~ 3 times closer to the GRB site than components III-VI. Component I is characterized also by the lack of Mg I absorption, unlike all other components. This may be both due to a closer distance and a lower density, suggesting a structured interstellar matter in this galaxy complex.
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| Data di pubblicazione: | 2009 | |
| Titolo: | The Prompt, High-Resolution Spectroscopic View of the "Naked-Eye" GRB080319B | |
| Autori: | D'Elia V.; Fiore F.; Perna R.; Krongold Y.; Covino S.; Fugazza D.; Lazzati D.; Nicastro F.; Antonelli L. A.; Campana S.; Chincarini G.; D'Avanzo P.; Della Valle M.; Goldoni P.; Guetta D.; Guidorzi C.; Meurs E. J. A.; Mirabel F.; Molinari E.; Norci L.; Piranomonte S.; Stella L.; Stratta G.; Tagliaferri G.; Ward P. | |
| Rivista: | THE ASTROPHYSICAL JOURNAL | |
| Parole Chiave: | gamma rays: bursts | |
| Abstract: | GRB080319B reached fifth optical magnitude during the burst prompt emission. Thanks to the Very Large Telescope (VLT)/Ultraviolet and Visual Echelle Spectrograph (UVES) rapid response mode, we observed its afterglow just 8m:30s after the gamma-ray burst (GRB) onset when the magnitude was R ~ 12. This allowed us to obtain the best signal-to-noise (S/N), high-resolution spectrum of a GRB afterglow ever (S/N per resolution element ~50). The spectrum is rich of absorption features belonging to the main system at z = 0.937, divided in at least six components spanning a total velocity range of 100 km s–1. The VLT/UVES observations caught the absorbing gas in a highly excited state, producing the strongest Fe II fine structure lines ever observed in a GRB. A few hours later, the optical depth of these lines was reduced by a factor of 4-20, and the optical/UV flux by a factor of ~60. This proves that the excitation of the observed fine structure lines is due to "pumping" by the GRB UV photons. A comparison of the observed ratio between the number of photons absorbed by the excited state and those in the Fe II ground state suggests that the six absorbers are ~2-6 kpc from the GRB site, with component I ~ 3 times closer to the GRB site than components III-VI. Component I is characterized also by the lack of Mg I absorption, unlike all other components. This may be both due to a closer distance and a lower density, suggesting a structured interstellar matter in this galaxy complex. | |
| Digital Object Identifier (DOI): | 10.1088/0004-637X/694/1/332 | |
| Handle: | http://hdl.handle.net/11392/535685 | |
| Appare nelle tipologie: | 03.1 Articolo su rivista |
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