GRB 051022: Physical Parameters and Extinction of a Prototype Dark Burst

Rol, E.; Horst, A. J. van der; Wiersema, K.; Patel, S.; Levan, A. J.; Nysewander, M.; Kouveliotou, C.; Wijers, R. A. M. J.; Tanvir, N. R.; Reichart, D. E.; Fruchter, A. S.; Graham, John F.; Ovaldsen, J. E.; Jaunsen, A. O.; Jonker, P. G.; Ham, Wilbert Van; Hjorth, J.; Starling, R. L. C.; O’Brien, P. T.; Fynbo, J. P. U.; Burrows, D. N.; Strom, R. G.

doi:10.1086/521336

Cited by 62 publications

(76 citation statements)

References 68 publications

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“…Indeed, the associated extinction will be high in these systems (Vladilo & Péroux 2005; see also Prochaska et al 2009) and their observation with high-resolution spectrographs, even with the advantage of fast response, possibly difficult. This is consistent with the findings of multi-colour photometry that a large fraction of bursts are dark because of high dust extinction in their hosts (Rol et al 2007;Jaunsen et al 2008;Tanvir et al 2008;Cenko et al 2009). If a bias exists in the UVES sample, it could also be against GRB-DLAs located at much smaller distances from their bursts than currently found because, as we have shown, high metal (resp.…”

Section: Summary and Prospectssupporting

confidence: 91%

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: Summary and Prospectssupporting

confidence: 91%

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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“…X-ray observations of GRB afterglows show neutral hydrogen column densities consistent those of Galactic giant molecular clouds (Galama & Wijers 2001;Jakobsson et al 2006;Schady et al 2007). At optical wavelengths, moderate extinction characteristic of dense regions is seen in some bursts (Kann et al 2007), while in others the afterglow appears significantly extinguished (Djorgovski et al 2001;Levan et al 2006a;Watson et al 2006;Pellizza et al 2006;Rol et al 2007), and at high redshifts where Lyα absorption can be found in the optical spectrum, large hydrogen column densities (up to 10 23 cm −3 ) are frequently found (cf. Jakobsson et al 2007).…”

Section: Summary and Discussionmentioning

confidence: 99%

A Comparison of the Afterglows of Short- And Long-Duration Gamma-Ray Bursts

Nysewander

Fruchter

Pe’er

2009

ApJ

158

204

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We present a comparative study of the observed properties of the optical and X-ray afterglows of short-and long-duration γ -ray bursts (GRBs). Using a large sample of 37 short and 421 long GRBs, we find a strong correlation between the afterglow brightness measured after 11 hr and the observed fluence of the prompt emission. Both the optical (R band) and X-ray flux densities (F R and F X ) scale with the γ -ray fluence, F γ . For bursts with a known redshift, a tight correlation exists between the afterglow flux densities at 11 hr (rest frame) and the total isotropic γ -ray energy, E γ,ISO : F R,X ∝ E γ,ISO α , with α 1. The constant of proportionality is nearly identical for long and short bursts, when E γ,ISO is obtained from the Swift data. Additionally, we find that for short busts with F γ 10 −7 erg cm −2 , optical afterglows are nearly always detected by reasonably deep early observations. Finally, we show that the ratio F R /F X has very similar values for short and long bursts. These results are difficult to explain in the framework of the standard scenario, since they require that either (1) the number density of the surrounding medium of short bursts is typically comparable to, or even larger than the number density of long bursts; (2) short bursts explode into a density profile, n(r) ∝ r −2 ; or (3) the prompt γ -ray fluence depends on the density of the external medium. We therefore find it likely that either basic assumptions on the properties of the circumburst environment of short GRBs or else the standard models of GRB emission must be re-examined. We believe that the most likely solution is that the ambient density surrounding typical short bursts is higher than has generally been expected: a typical value of ∼1 cm −3 is indicated. We discuss recent modifications to the standard binary merger model for short bursts which may be able to explain the implied density.

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“…While many of these non-detections are simply due to the lack of rapid and deep optical follow-up observations, some events (after correction for Galactic extinction) are truly optically dark (e.g., Fynbo et al 2001;De Pasquale et al 2003;Castro-Tirado et al 2007;Rol et al 2007;Hashimoto et al 2010;Holland et al 2010).…”

Section: Bursts With Optically Undetected Afterglowsmentioning

confidence: 99%

A deep search for the host galaxies of gamma-ray bursts with no detected optical afterglow

Rossi

Klose

Ferrero

et al. 2012

A&A

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Context. Gamma-ray bursts (GRBs) can provide information about star formation at high redshifts. Even in the absence of a bright optical/nearinfrared/radio afterglow, the high detection rate of X-ray afterglows by Swift/XRT and its localization precision of 2-3 arcsec facilitates the identification and the study of GRB host galaxies. Aims. We focus on the search for the host galaxies of 17 bursts with arcsec-sized XRT error circles but no detected long-wavelength afterglow, in spite of their deep and rapid follow-up observations. Three of these events can also be classified as truly dark bursts, i.e., the observed upper limit on the optical flux of the afterglow was less than expected based on the measured X-ray flux. Our goals are to identify the GRB host galaxy candidates and characterize their phenomenological parameters. Methods. Our study is based on deep R C and K s -band observations performed with FORS1, FORS2, VIMOS, ISAAC, and HAWK-I at the ESO/VLT, partly supported by observations with the seven-channel imager GROND at the 2.2-m telescope on La Silla, and supplemented by observations with NEWFIRM at the 4-m telescope on Kitt Peak. To be conservative, we searched for host galaxy candidates within an area of twice the radius of each associated 90% c.l. Swift/XRT error circle. Results. For 15 of the 17 bursts, we find at least one galaxy within the searching area, and in the remaining two cases only a deep upper limit to R C and K s can be provided. In seven cases, we discover extremely red objects in the error circles, at least four of which might be dust-enshrouded galaxies. The most remarkable case is the host of GRB 080207, which has a color of (R C − K s ) AB ∼ 4.7 mag, and is one of the reddest galaxies ever associated with a GRB. As a by-product of our study we identify the optical afterglow of GRB 070517. Conclusions. Only a minority of optically dim afterglows are due to Lyman dropout ( 1/3). Extinction by dust in the host galaxies might explain all other events. Thereby, a seemingly non-negligible fraction of these hosts are globally dust-enshrouded, extremely red galaxies. This suggests that at least a fraction of GRB afterglows trace a subpopulation of massive starburst galaxies, which are markedly different from the main body of the GRB host galaxy population, namely the blue, subluminous, compact galaxies.

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GRB 051022: Physical Parameters and Extinction of a Prototype Dark Burst

Cited by 62 publications

References 68 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

A Comparison of the Afterglows of Short- And Long-Duration Gamma-Ray Bursts

A deep search for the host galaxies of gamma-ray bursts with no detected optical afterglow

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