TY - JOUR
T1 - THE PROMPT, HIGH-RESOLUTION SPECTROSCOPIC VIEW OF THE "NAKED-EYE" GRB080319B
AU - D'Elia, V.
AU - Fiore, F.
AU - Perna, R.
AU - Krongold, Y.
AU - Covino, S.
AU - Fugazza, D.
AU - Lazzati, D.
AU - Nicastro, F.
AU - Antonelli, L. A.
AU - Campana, S.
AU - Chincarini, G.
AU - D'Avanzo, P.
AU - Della Valle, M.
AU - Goldoni, P.
AU - Guetta, D.
AU - Guidorzi, C.
AU - Meurs, E. J. A.
AU - Mirabel, F.
AU - Molinari, E.
AU - Norci, L.
AU - Piranomonte, S.
AU - Stella, L.
AU - Stratta, G.
AU - Tagliaferri, G.
AU - Ward, P.
PY - 2009/3/20
Y1 - 2009/3/20
N2 - 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 FeII 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 FeII 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 MgI 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.
AB - 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 FeII 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 FeII 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 MgI 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.
KW - gamma rays: bursts
UR - https://www.scopus.com/pages/publications/70350239546
U2 - 10.1088/0004-637X/694/1/332
DO - 10.1088/0004-637X/694/1/332
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SN - 0004-637X
VL - 694
SP - 332
EP - 338
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
ER -