VLT/X-shooter spectroscopy of the GRB 120327A afterglow

V. D'Elia; Johan Peter Uldall Fynbo; P. Goldoni; S. Covino; A. de Ugarte Postigo; C. Ledoux; F. Calura; J. Gorosabel; D. Malesani; F. Matteucci R. Sanchez-Ramirez; S. Savaglio; A. J. Castro-Tirado; O. E. Hartoog; L. Kaper; T. Munoz-Darias; E. Pian; S. Piranomonte; G. Tagliaferri; N. Tanvir; S. D. Vergani; D. J. Watson; Dong Xu

doi:10.1051/0004-6361/201323057

VLT/X-shooter spectroscopy of the GRB 120327A afterglow

V. D'Elia, Johan Peter Uldall Fynbo, P. Goldoni, S. Covino, A. de Ugarte Postigo, C. Ledoux, F. Calura, J. Gorosabel, D. Malesani, F. Matteucci R. Sanchez-Ramirez, S. Savaglio, A. J. Castro-Tirado, O. E. Hartoog, L. Kaper, T. Munoz-Darias, E. Pian, S. Piranomonte, G. Tagliaferri, N. Tanvir, S. D. VerganiD. J. Watson, Dong Xu

DARK

39 Citationer (Scopus)

Abstract

We present a study of the environment of the Swift long gamma-ray burst GRB 120327A at z ~2.8 through optical spectroscopy of its afterglow. We analyzed medium-resolution, multi-epoch spectroscopic observations (~7000 - 12000, corresponding to ~ 15 - 23 km/s, S/N = 15- 30 and wavelength range 3000-25000AA) of the optical afterglow of GRB 120327A, taken with X-shooter at the VLT 2.13 and 27.65 hr after the GRB trigger. The first epoch spectrum shows that the ISM in the GRB host galaxy at z = 2.8145 is extremely rich in absorption features, with three components contributing to the line profiles. The hydrogen column density associated with GRB 120327A has log NH / cm^(-2) = 22.01 +/- 0.09, and the metallicity of the host galaxy is in the range [X/H] = -1.3 to -1.1. In addition to the ground state lines, we detect absorption features associated with excited states of CII, OI, SiII, FeII, and NiII, which we used to derive information on the distance between the host absorbing gas and the site of the GRB explosion. The variability of the FeI\lambda2396 excited line between the two epochs proves that these features are excited by the GRB UV flux. Moreover, the distance of component I is found to be dI=200+100-60 pc, while component II is located closer to the GRB, at dII=100+40-30 pc. These values are among the lowest found in GRBs. Component III does not show excited transitions, so it should be located farther away from the GRB. The presence of H2 molecules is firmly established, with a molecular fraction in the range f=4 X 10^(-7) - 10^(-4). This particularly low value can be attributed to the small dust content. This represents the third positive detection of molecules in a GRB environment.

Originalsprog	Engelsk
Tidsskrift	Astronomy & Astrophysics
Vol/bind	564
Sider (fra-til)	38-56
Antal sider	18
ISSN	0004-6361
DOI	https://doi.org/10.1051/0004-6361/201323057
Status	Udgivet - apr. 2014

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astro-ph.HE
astro-ph.CO
astro-ph.GA

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10.1051/0004-6361/201323057

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D'Elia, V., Fynbo, J. P. U., Goldoni, P., Covino, S., Postigo, A. D. U., Ledoux, C., Calura, F., Gorosabel, J., Malesani, D., Sanchez-Ramirez, F. M. R., Savaglio, S., Castro-Tirado, A. J., Hartoog, O. E., Kaper, L., Munoz-Darias, T., Pian, E., Piranomonte, S., Tagliaferri, G., Tanvir, N., ... Xu, D. (2014). VLT/X-shooter spectroscopy of the GRB 120327A afterglow. Astronomy & Astrophysics, 564, 38-56. https://doi.org/10.1051/0004-6361/201323057

D'Elia, V, Fynbo, JPU, Goldoni, P, Covino, S, Postigo, ADU, Ledoux, C, Calura, F, Gorosabel, J, Malesani, D, Sanchez-Ramirez, FMR, Savaglio, S, Castro-Tirado, AJ, Hartoog, OE, Kaper, L, Munoz-Darias, T, Pian, E, Piranomonte, S, Tagliaferri, G, Tanvir, N, Vergani, SD, Watson, DJ & Xu, D 2014, 'VLT/X-shooter spectroscopy of the GRB 120327A afterglow', Astronomy & Astrophysics, bind 564, s. 38-56. https://doi.org/10.1051/0004-6361/201323057

@article{1740231b56ca4815b7b6189496e57820,

title = "VLT/X-shooter spectroscopy of the GRB 120327A afterglow",

abstract = "Aims. We present a study of the environment of the Swift long gamma-ray burst GRB 120327A at z 2.8 through optical spectroscopy of its afterglow. Methods. We analyzed medium-resolution, multi-epoch spectroscopic observations (R ∼ 7000-12 000, corresponding to ∼15-23 km s-1, S/N = 15-30 and wavelength range 3000-25 000 {\AA}) of the optical afterglow of GRB 120327A, taken with X-shooter at the VLT 2.13 and 27.65 hr after the GRB trigger. Results. The first epoch spectrum shows that the ISM in the GRB host galaxy at z = 2.8145 is extremely rich in absorption features, with three components contributing to the line profiles. The hydrogen column density associated with GRB 120327A has log NH/cm-2 = 22.01 ± 0.09, and the metallicity of the host galaxy is in the range [X/H] =-1.3 to-1.1. In addition to the ground state lines, we detect absorption features associated with excited states of C ii, O i, Si ii, Fe ii, and Ni ii, which we used to derive information on the distance between the host absorbing gas and the site of the GRB explosion. The variability of the Fe iiλ2396 excited line between the two epochs proves that these features are excited by the GRB UV flux. Moreover, the distance of component I is found to be d I = 200+100-60 pc, while component II is located closer to the GRB, at dII = 100+40-30 pc. These values are among the lowest found in GRBs. Component III does not show excited transitions, so it should be located farther away from the GRB. The presence of H2 molecules is firmly established, with a molecular fraction f in the range f = 4 × 10-7-10-4. This particularly low value can be attributed to the small dust content. This represents the third positive detection of molecules in a GRB environment.",

keywords = "astro-ph.HE, astro-ph.CO, astro-ph.GA",

author = "V. D'Elia and Fynbo, {Johan Peter Uldall} and P. Goldoni and S. Covino and Postigo, {A. de Ugarte} and C. Ledoux and F. Calura and J. Gorosabel and D. Malesani and Sanchez-Ramirez, {F. Matteucci R.} and S. Savaglio and Castro-Tirado, {A. J.} and Hartoog, {O. E.} and L. Kaper and T. Munoz-Darias and E. Pian and S. Piranomonte and G. Tagliaferri and N. Tanvir and Vergani, {S. D.} and Watson, {D. J.} and Dong Xu",

year = "2014",

month = apr,

doi = "10.1051/0004-6361/201323057",

language = "English",

volume = "564",

pages = "38--56",

journal = "Astronomy and Astrophysics Supplement Series",

issn = "0004-6361",

publisher = "E D P Sciences",

}

TY - JOUR

T1 - VLT/X-shooter spectroscopy of the GRB 120327A afterglow

AU - D'Elia, V.

AU - Fynbo, Johan Peter Uldall

AU - Goldoni, P.

AU - Covino, S.

AU - Postigo, A. de Ugarte

AU - Ledoux, C.

AU - Calura, F.

AU - Gorosabel, J.

AU - Malesani, D.

AU - Sanchez-Ramirez, F. Matteucci R.

AU - Savaglio, S.

AU - Castro-Tirado, A. J.

AU - Hartoog, O. E.

AU - Kaper, L.

AU - Munoz-Darias, T.

AU - Pian, E.

AU - Piranomonte, S.

AU - Tagliaferri, G.

AU - Tanvir, N.

AU - Vergani, S. D.

AU - Watson, D. J.

AU - Xu, Dong

PY - 2014/4

Y1 - 2014/4

N2 - Aims. We present a study of the environment of the Swift long gamma-ray burst GRB 120327A at z 2.8 through optical spectroscopy of its afterglow. Methods. We analyzed medium-resolution, multi-epoch spectroscopic observations (R ∼ 7000-12 000, corresponding to ∼15-23 km s-1, S/N = 15-30 and wavelength range 3000-25 000 Å) of the optical afterglow of GRB 120327A, taken with X-shooter at the VLT 2.13 and 27.65 hr after the GRB trigger. Results. The first epoch spectrum shows that the ISM in the GRB host galaxy at z = 2.8145 is extremely rich in absorption features, with three components contributing to the line profiles. The hydrogen column density associated with GRB 120327A has log NH/cm-2 = 22.01 ± 0.09, and the metallicity of the host galaxy is in the range [X/H] =-1.3 to-1.1. In addition to the ground state lines, we detect absorption features associated with excited states of C ii, O i, Si ii, Fe ii, and Ni ii, which we used to derive information on the distance between the host absorbing gas and the site of the GRB explosion. The variability of the Fe iiλ2396 excited line between the two epochs proves that these features are excited by the GRB UV flux. Moreover, the distance of component I is found to be d I = 200+100-60 pc, while component II is located closer to the GRB, at dII = 100+40-30 pc. These values are among the lowest found in GRBs. Component III does not show excited transitions, so it should be located farther away from the GRB. The presence of H2 molecules is firmly established, with a molecular fraction f in the range f = 4 × 10-7-10-4. This particularly low value can be attributed to the small dust content. This represents the third positive detection of molecules in a GRB environment.

AB - Aims. We present a study of the environment of the Swift long gamma-ray burst GRB 120327A at z 2.8 through optical spectroscopy of its afterglow. Methods. We analyzed medium-resolution, multi-epoch spectroscopic observations (R ∼ 7000-12 000, corresponding to ∼15-23 km s-1, S/N = 15-30 and wavelength range 3000-25 000 Å) of the optical afterglow of GRB 120327A, taken with X-shooter at the VLT 2.13 and 27.65 hr after the GRB trigger. Results. The first epoch spectrum shows that the ISM in the GRB host galaxy at z = 2.8145 is extremely rich in absorption features, with three components contributing to the line profiles. The hydrogen column density associated with GRB 120327A has log NH/cm-2 = 22.01 ± 0.09, and the metallicity of the host galaxy is in the range [X/H] =-1.3 to-1.1. In addition to the ground state lines, we detect absorption features associated with excited states of C ii, O i, Si ii, Fe ii, and Ni ii, which we used to derive information on the distance between the host absorbing gas and the site of the GRB explosion. The variability of the Fe iiλ2396 excited line between the two epochs proves that these features are excited by the GRB UV flux. Moreover, the distance of component I is found to be d I = 200+100-60 pc, while component II is located closer to the GRB, at dII = 100+40-30 pc. These values are among the lowest found in GRBs. Component III does not show excited transitions, so it should be located farther away from the GRB. The presence of H2 molecules is firmly established, with a molecular fraction f in the range f = 4 × 10-7-10-4. This particularly low value can be attributed to the small dust content. This represents the third positive detection of molecules in a GRB environment.

KW - astro-ph.HE

KW - astro-ph.CO

KW - astro-ph.GA

U2 - 10.1051/0004-6361/201323057

DO - 10.1051/0004-6361/201323057

M3 - Journal article

SN - 0004-6361

VL - 564

SP - 38

EP - 56

JO - Astronomy and Astrophysics Supplement Series

JF - Astronomy and Astrophysics Supplement Series

ER -

VLT/X-shooter spectroscopy of the GRB 120327A afterglow

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