2010A&A...523A..36D


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.12CEST12:44:32

2010A&A...523A..36D - Astronomy and Astrophysics, volume 523, A36-36 (2010/11-2)

VLT/X-shooter spectroscopy of the GRB 090926A afterglow.

D'ELIA V., FYNBO J.P.U., COVINO S., GOLDONI P., JAKOBSSON P., MATTEUCCI F., PIRANOMONTE S., SOLLERMAN J., THOENE C.C., VERGANI S.D., VREESWIJK P.M., WATSON D.J., WIERSEMA K., ZAFAR T., DE UGARTE POSTIGO A., FLORES H., HJORTH J., KAPER L., LEVAN A.J., MALESANI D., MILVANG-JENSEN B., PIAN E., TAGLIAFERRI G. and TANVIR N.R.

Abstract (from CDS):

The aim of this paper is to study the environment and intervening absorbers of the gamma-ray burst GRB 090926A through analyzing optical spectra of its afterglow. We analyzed medium-resolution spectroscopic observations (R=10000, corresponding to 30km/s, S/N=15-30 and wavelength range 3000-25000) of the optical afterglow of GRB090926A, taken with X-shooter at the VLT∼22 h after the GRB trigger. The spectrum shows that the ISM in the GRB host galaxy at z=2.1071 is rich in absorption features, with two components contributing to the line profiles. In addition to the ground state lines, we detect CII, OI, SiII, FeII, and NiII-excited absorption features, which we used to derive information on the distance between the host absorbing gas and the site of the GRB explosion. The distance of component I is found to be 2.40±0.15kpc, while component II is located far away from the GRB, possibly at ∼5kpc. These values are compatible with those found for other GRBs. The hydrogen column density associated to GRB090926A is logNH(cm–2)=21.60±0.07, and the metallicity of the host galaxy is in the range [X/H]=-2.5 to -1.9 with respect to the solar values, i.e., among the lowest values ever observed for a GRB host galaxy. A comparison with galactic chemical evolution models has suggested that the host of GRB090926A is likely to be a dwarf-irregular galaxy. No emission lines were detected, but a Hα flux in emission of 9x10–18erg/s/cm2 (i.e., a star-formation rate of 2M/yr), which is typical of many GRB hosts, would have been detected in our spectra, and thus emission lines are well within the reach of X-shooter. We put an upper limit to the Hmolecular fraction of the host galaxy ISM, which is f<7x10–7. The continuum has been fitted assuming a power-law spectrum, with a spectral index of β=0.89+0.02–0.02. The best fit does essentially not require any intrinsic extinction because EB–V<0.01mag adopting a SMC extinction curve. Finally, the line of sight of GRB090926A presents four weak intervening absorption systems in the redshift range 1.24<z<1.95.

Abstract Copyright:

Journal keyword(s): ISM: abundances - ISM: atoms - galaxies: star formation - line: profiles - techniques: spectroscopic - atomic processes

Simbad objects: 13

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Number of rows : 13

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 9446 1
2 GRB 050904 gB 00 54 50.794 +14 05 09.42           ~ 431 1
3 GRB 070802 gB 02 27 35.91 -55 31 39.1           ~ 136 0
4 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 14832 1
5 GRB 080330 gB 11 17 06.70 +30 36 24.1           ~ 119 0
6 GRB 080607 gB 12 59 47.14 +15 55 09.6           ~ 209 0
7 GRB 090313 gB 13 13 36.00 +08 05 10.7           ~ 116 0
8 GRB 060206 gB 13 31 43.420 +35 03 03.60   19.99 17.09     ~ 282 1
9 GRB 050730 gB 14 08 17.090 -03 46 18.90   20.32 17.68     ~ 282 1
10 GRB 080319B gB 14 31 41.04 +36 18 09.2           ~ 421 0
11 GRB 060418 gB 15 45 42.600 -03 38 20.00 15.73 16.19 14.98     ~ 322 1
12 GRB 050922C gB 21 09 33.000 -08 45 30.10 15.15 15.86 14.69     ~ 250 0
13 GRB 090926A gB 23 33 36.18 -66 19 25.9           ~ 250 0

    Equat.    Gal    SGal    Ecl

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2020.07.12-12:44:32

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