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

D’Elia, V.; Fynbo, J. P. U.; Covino, S.; Goldoni, P.; Jakobsson, P.; Matteuccí, F.; Piranomonte, S.; Sollerman, J.; Thoene, C. C.; Vergani, S. D.; Vreeswijk, P. M.; Watson, Derrick G.; Wiersema, K.; Zafar, T.; Postigo, A. de Ugarte; Flores, H.; Hjorth, J.; Kaper, L.; Levan, A. J.; Malesani, D.; Milvang-Jensen, B.; Pian, E.; Tagliaferri, G.; Tanvir, N. R.

doi:10.1051/0004-6361/201015216

Cited by 54 publications

(26 citation statements)

References 60 publications

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“…In future, better rest-frame UV through NIR data will allow us to obtain reasonable numbers of extinction curves of individual events (see Section 5.2 of Zafar et al 2011). In support of this objective the X-shooter spectrograph on the VLT is now regularly obtaining UV through NIR spectra of GRB afterglows (e.g., de Ugarte Postigo et al 2010;D'Elia et al 2010).…”

Section: Comparison With Local Group Sightlinesmentioning

confidence: 94%

The Properties of the 2175 Å Extinction Feature Discovered in GRB Afterglows

Zafar

Watson

Elíasdóttir

et al. 2012

ApJ

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The unequivocal, spectroscopic detection of the 2175 Å bump in extinction curves outside the Local Group is rare. To date, the properties of the bump have been examined in only two gamma-ray burst (GRB) afterglows (GRB 070802 and GRB 080607). In this work, we analyze in detail the detections of the 2175 Å extinction bump in the optical spectra of two further GRB afterglows: GRB 080605 and 080805. We gather all available optical/nearinfrared photometric, spectroscopic, and X-ray data to construct multi-epoch spectral energy distributions (SEDs) for both GRB afterglows. We fit the SEDs with the Fitzpatrick & Massa model with a single or broken power law. We also fit a sample of 38 GRB afterglows, known to prefer a Small Magellanic Cloud (SMC)-type extinction curve, with the same model. We find that the SEDs of GRB 080605 and GRB 080805 at two epochs are fit well with a single power law with a derived extinction of A V = 0.52 −0.6 and 1.5 ± 0.2, respectively. While the slope of the extinction curve of GRB 080805 is not well constrained, the extinction curve of GRB 080605 has an unusual very steep far-UV rise together with the 2175 Å bump. Such an extinction curve has previously been found in only a small handful of sightlines in the Milky Way. One possible explanation of such an extinction curve may be dust arising from two different regions with two separate grain populations, however we cannot distinguish the origin of the curve. We finally compare the four 2175 Å bump sightlines to the larger GRB afterglow sample and to Local Group sightlines. We find that while the width and central positions of the bumps are consistent with what is observed in the Local Group, the relative strength of the detected bump (A bump ) for GRB afterglows is weaker for a given A V than for almost any Local Group sightline. Such dilution of the bump strength may offer tentative support to a dual dust-population scenario.

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Section: Comparison With Local Group Sightlinesmentioning

confidence: 94%

The Properties of the 2175 Å Extinction Feature Discovered in GRB Afterglows

Zafar

Watson

Elíasdóttir

et al. 2012

ApJ

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“…The case of GRB 090926A is a good example of the X-shooter capabilities in this context (D'Elia et al 2010). Moreover, a paper exploiting the full X-shooter GRB sample to address these issues is currently in preparation (Watson et al in prep.).…”

Section: The Extinction Curve Shapementioning

confidence: 99%

“…Monitoring these variations and comparing them with predictions from photoexcitation codes enables one to derive information on the distance between the GRB and the absorbing material. This distance can be estimated even when multi-epoch spectroscopy is not available, under the assumption that UV pumping is the responsible mechanism for the production of the excited lines (D'Elia et al 2009b(D'Elia et al , 2010(D'Elia et al , 2011Ledoux et al 2009). …”

Section: Introductionmentioning

confidence: 99%

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

D’Elia

Fynbo

Goldoni

et al. 2014

A&A

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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 N H /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 ii λ2396 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 d II = 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 H 2 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.

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“…Field galaxies are shown as gray dots (Savaglio et al 2005;Pérez-Montero et al 2009;Mannucci et al 2009;Hayashi et al 2009;Richard et al 2011), and in similar metallicity scales as the GRB measurements. Absorption metallicities from GRB afterglows (Rau et al 2010;D'Elia et al 2010;Savaglio et al 2012;Thöne et al 2012, and references therein) and QSOs (Prochaska et al 2003) are plotted as black and gray diamonds, respectively. Errorbars for individual events in the comparison samples are omitted to enhance clarity.…”

Section: The Host Of Grb 080605 Within the Sample Of Grb Hostsmentioning

confidence: 99%

The metal-enriched host of an energeticγ-ray burst atz ≈ 1.6

Krühler¹,

Fynbo²,

Geier³

et al. 2012

A&A

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Context. The star-forming nature of long γ-ray burst (GRB) host galaxies provides invaluable constraints on the progenitors of GRBs and might open a short-cut to the characteristics of typical star-forming galaxies throughout the history of the Universe. Due to the absence of near-infrared (NIR) spectroscopy, however, detailed investigations, specifically a determination of the gas-phase metallicity of gamma-ray burst hosts, was largely limited to redshifts z < 1 to date. Aims. We observed the galaxy hosting GRB 080605 at z = 1.64 using optical/NIR spectroscopy and high-resolution HST/WFC3 imaging in the rest-frame wavelength range between 1150 and 8700 Å. These data allow us to study a z > 1 GRB host in unprecedented detail and investigate the relation between GRB hosts and field galaxies. Methods. We availed of VLT/X-shooter optical/NIR spectroscopy to measure the metallicity, electron density, star-formation rate (SFR), and reddening of the host of GRB 080605. Specifically, we used different strong-line diagnostics to robustly measure the gas-phase metallicity within the interstellar medium (ISM) for the first time based on [N ii] at this redshift.Results. The host of the energetic (E γ,iso ∼ 2 × 10 53 erg) GRB 080605 at z ∼ 1.64 is a morphologically complex, vigorously starforming galaxy with an Hα-derived SFR of 31 +12 −6 M yr −1 . Its ISM is significantly enriched with metals. Specifically, [N ii]/Hα = 0.14 ± 0.02, which yields an oxygen abundance 12 + log(O/H) between 8.3 and 8.6 depending on the adopted strong-line calibrator. This corresponds to values in the range of 0.4−0.8 Z . For its measured stellar mass (M * = 8.0 +1.3 −1.6 × 10 9 M ) and SFR, this value is consistent with the fundamental metallicity relation defined by star-forming field galaxies. The absence of strong Lyα emission constrains the escape fraction of resonantly-scattered Lyα photons to f esc < ∼ 0.08. Conclusions. Our observations provide a detailed picture of the conditions in the ISM of a highly star-forming galaxy with irregular morphology at z ∼ 1.6. They include the first robust metallicity measurement based on [N ii] for a GRB host at z > 1 and directly illustrate that GRB hosts are not necessarily metal-poor, both on absolute scales as well as relative to their stellar mass and SFR. GRB hosts could thus be fair tracers of the population of ordinary star-forming galaxies at high redshift.

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

Cited by 54 publications

References 60 publications

The Properties of the 2175 Å Extinction Feature Discovered in GRB Afterglows

The Properties of the 2175 Å Extinction Feature Discovered in GRB Afterglows

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

The metal-enriched host of an energeticγ-ray burst atz ≈ 1.6

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