High Column Densities and Low Extinctions of Gamma-Ray Bursts: Evidence for Hypernovae and Dust Destruction

Galama, T. J.; Wijers, R. A. M. J.

doi:10.1086/319162

Cited by 209 publications

(257 citation statements)

References 50 publications

(35 reference statements)

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“…As most star formation occurs within molecular clouds, it is generally expected that the latter are the birthplaces of many GRBs. However, although various studies (Galama & Wijers 2001;Reichart & Price 2002) have argued in favour of a link between molecular clouds and GRBs, compelling observational evidence such as the detection of molecular hydrogen (H 2 ) in GRB optical spectra is lacking (Vreeswijk et al 2004;Tumlinson et al 2007). As absorption lines related to ground-state or vibrationally excited H 2 energy levels should be detectable (Draine & Hao 2002), the absence of detection so far suggests that any H 2 molecules in the immediate vicinity of a GRB are dissociated by the intense X-ray/UV afterglow flux.…”

Section: Introductionmentioning

confidence: 99%

Physical conditions in high-redshift GRB-DLA absorbers observed with VLT/UVES: implications for molecular hydrogen searches

Ledoux¹,

Vreeswijk

Smette³

et al. 2009

A&A

160

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Aims. We aim to understand the nature of the absorbing neutral gas in the galaxies hosting high-redshift long-duration gamma-ray bursts (GRBs) and to determine their physical conditions. Methods. A detailed analysis of high-quality VLT/UVES spectra of the optical afterglow of GRB 050730 and other Swift-era bursts is presented. Results. We report the detection of a significant number of previously unidentified allowed transition lines of Fe + , involving the fine structure of the ground term ( 6 D 7/2 , 6 D 5/2 , 6 D 3/2 , 6 D 1/2 ) and that of other excited levels ( 4 F 9/2 , 4 F 7/2 , 4 F 5/2 , 4 F 3/2 , 4 D 7/2 , 4 D 5/2 ), from the z abs = 3.969, log N(H 0 ) = 22.10, damped Lyman-α (DLA) system located in the host galaxy of GRB 050730. No molecular hydrogen (H 2 ) is detected down to a molecular fraction of log f < −8.0. We derive accurate metal abundances for Fe + , S + , N 0 , Ni + , and, for the first time in this system, Si + and Ar 0 . The absorption lines are best-fit as a single narrow velocity component at z abs = 3.96857. The time-dependent evolution of the observed Fe + energy-level populations is modelled by assuming the excitation mechanism is fluorescence following excitation by ultraviolet photons emitted by the afterglow of GRB 050730. This UV pumping model successfully reproduces the observations, yielding a total Fe + column density of log N = 15.49 ± 0.03, a burst/cloud distance (defined to the near-side of the cloud) of d = 440 ± 30 pc, and a linear cloud size of l = 520 +240 −190 pc. This application of our photoexcitation code demonstrates that burst/DLA distances can be determined without strong constraints on absorption-line variability provided enough energy levels are detected. From the cloud size, we infer a particle density of n H ≈ 5−15 cm −3 . Conclusions.We discuss these results in the context of no detections of H 2 and C i lines (with log N(C 0 )/N(S + ) < −3) in a sample of seven z > 1.8 GRB host galaxies observed with VLT/UVES. We show that the lack of H 2 can be explained by the low metallicities, [X/H] < −1, low depletion factors, and, at most, moderate particle densities of the systems. This points to a picture where GRB-DLAs typically exhibiting very high H 0 column densities are diffuse metal-poor atomic clouds with high kinetic temperatures, T kin > ∼ 1000 K, and large physical extents, l > ∼ 100 pc. The properties of GRB-DLAs observed at high spectral resolution towards bright GRB afterglows differ markedly from the high metal and dust contents of GRB-DLAs observed at lower resolution. This difference likely results from the effect of a bias, against systems of high metallicity and/or close to the GRB, due to dust obscuration in the magnitudelimited GRB afterglow samples observed with high-resolution spectrographs.

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Section: Introductionmentioning

confidence: 99%

Physical conditions in high-redshift GRB-DLA absorbers observed with VLT/UVES: implications for molecular hydrogen searches

Ledoux¹,

Vreeswijk

Smette³

et al. 2009

A&A

160

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“…It is found that the optical extinctions are 10∼100 times smaller than expected from X-ray absorption (Galama et al 2001). We examine the X-ray absorptions in our GRB sample.…”

Section: Conclusion and Discussionmentioning

confidence: 94%

The Early X-ray Afterglows of Optically Bright and Dark Gamma-Ray Bursts

2006

Chin. J. Astron. Astrophys.

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“…A number of GRB sightlines exhibit X-ray absorption with implied metal column densities that significantly exceed the neutral ISM column densities measured from optical spectra (Watson et al 2007, Galama & Wijers, 2001). These observations provide hints for a large reservoir of highly ionized gas near the GRB.…”

Section: Ionized Gasmentioning

confidence: 98%

Probing the Interstellar Medium and Stellar Environments of Long-Duration GRBs

2007

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Abstract.We review the properties of the gas surrounding high-redshift gamma-ray bursts (GRBs) assessed through the analysis of damped Lyman-alpha systems (DLAs) identified in their afterglow spectra. These GRB-DLAs are characterized by large H I column densities with a median of N (H I) = 10 21. 7 cm −2 , no molecular gas signatures, metallicities ranging from 1/100 to nearly solar with a median exceeding 1/10 solar, and no anomalous abundance patterns. The detection of the atomic Mg lines and the time-variability of the fine-structure lines demonstrates that the majority of the neutral gas along the GRB sightlines is located between 50 pc and a few kpc from the GRB. This implies that this gas is presumably associated with the ambient interstellar medium of the host galaxy and that the derived properties from low-ionization lines do not directly constrain the local environment of the GRB progenitor. The highly ionized gas, traced by N V lines, which could result from a pre-existing H II region produced by the GRB progenitor and neighboring OB stars, appears on the other hand to be very local to the GRB at about 10 pc, yielding a snapshot of the medium's physical conditions at this radius.

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High Column Densities and Low Extinctions of Gamma-Ray Bursts: Evidence for Hypernovae and Dust Destruction

Cited by 209 publications

References 50 publications

Physical conditions in high-redshift GRB-DLA absorbers observed with VLT/UVES: implications for molecular hydrogen searches

Physical conditions in high-redshift GRB-DLA absorbers observed with VLT/UVES: implications for molecular hydrogen searches

The Early X-ray Afterglows of Optically Bright and Dark Gamma-Ray Bursts

Probing the Interstellar Medium and Stellar Environments of Long-Duration GRBs

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