Rapid-response mode VLT/UVES spectroscopy of GRB 060418 (<i>Corrigendum</i>)

Vreeswijk, P.M.; Ledoux, C.; Smette, A.; Ellison, Sara L.; Jaunsen, A. O.; Andersen, M. I.; Fruchter, A. S.; Fynbo, J. P. U.; Hjorth, J.; Kaufer, A.; Møller, P.; Petitjean, P.; Savaglio, S.; Wijers, R. A. M. J.

doi:10.1051/0004-6361/20066780e

Cited by 18 publications

(25 citation statements)

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“…This is consistent with distances inferred from variable fine-structure lines for other bursts (e.g. Vreeswijk et al 2007;D'Elia et al 2007;Vreeswijk et al 2011;De Cia et al 2012). The X-ray and UV afterglow may destroy dust out to ∼100 pc, but this is not always the case as discussed in Fruchter et al (2001).…”

Section: Origin and Variability Of The Flux Dropsupporting

confidence: 88%

The mysterious optical afterglow spectrum of GRB 140506A atz= 0.889

Fynbo

Krühler

Leighly

et al. 2014

A&A

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Context. Gamma-ray burst (GRB) afterglows probe sightlines to star-forming regions in distant star-forming galaxies. Here we present a study of the peculiar afterglow spectrum of the z = 0.889 Swift GRB 140506A. Aims. Our aim is to understand the origin of the very unusual properties of the absorption along the line of sight. Methods. We analyse spectroscopic observations obtained with the X-shooter spectrograph mounted on the ESO/VLT at two epochs 8.8 h and 33 h after the burst, and with imaging from the GROND instrument. We also present imaging and spectroscopy of the host galaxy obtained with the Magellan telescope. Results. The underlying afterglow appears to be a typical afterglow of a long-duration GRB. However, the material along the line of sight has imprinted very unusual features on the spectrum. First, there is a very broad and strong flux drop below 8000 Å (∼4000 Å in the rest frame), which seems to be variable between the two spectroscopic epochs. We can reproduce the flux-drops both as a giant 2175 Å extinction bump and as an effect of multiple scattering on dust grains in a dense environment. Second, we detect absorption lines from excited H i and He i. We also detect molecular absorption from CH + . Conclusions. We interpret the unusual properties of these spectra as reflecting the presence of three distinct regions along the line of sight: the excited He i absorption originates from an H ii-region, whereas the Balmer absorption must originate from an associated photodissociation region.The strong metal line and molecular absorption and the dust extinction must originate from a third, cooler region along the line of sight. The presence of at least three separate regions is reflected in the fact that the different absorption components have different velocities relative to the systemic redshift of the host galaxy.

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Section: Origin and Variability Of The Flux Dropsupporting

confidence: 88%

The mysterious optical afterglow spectrum of GRB 140506A atz= 0.889

Fynbo

Krühler

Leighly

et al. 2014

A&A

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“…As our team has already performed such modelling on GRB 060418 (at z = 1.490, Vreeswijk et al 2007Vreeswijk et al , 2011, we can readily determine this limit on H  for this sightline. The UV34 triplet is not detected in the GRB 060418 UVES spectra, with a 3σ upper limit on the rest-frame equivalent width (column density) of 0.03 Å (log N = 12.6).…”

Section: Discussionmentioning

confidence: 96%

“…There are, however, two major differences. First, we include the correct excitation flux (see the erratum published by Vreeswijk et al 2011), resulting in a distance decrease of √ 4π with respect to the old excitation calculation. Second, instead of calculating the excitation at line centre only, we effectively integrate over the full line profile to obtain the actual flux that is entering a particular layer.…”

Section: Photo-excitationmentioning

confidence: 99%

Time-dependent excitation and ionization modelling of absorption-line variability due to GRB 080310

Vreeswijk

Ledoux

Raassen

et al. 2012

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We model the time-variable absorption of Fe , Fe , Si , C  and Cr  detected in Ultraviolet and Visual Echelle Spectrograph (UVES) spectra of gamma-ray burst (GRB) 080310, with the afterglow radiation exciting and ionizing the interstellar medium in the host galaxy at a redshift of z = 2.42743. To estimate the rest-frame afterglow brightness as a function of time, we use a combination of the optical VRI photometry obtained by the RAPTOR-T telescope array, which is presented in this paper, and Swift's X-Ray Telescope (XRT) observations. Excitation alone, which has been successfully applied for a handful of other GRBs, fails to describe the observed column density evolution in the case of GRB 080310. Inclusion of ionization is required to explain the column density decrease of all observed Fe  levels (including the ground state 6 D 9/2 ) and increase of the Fe  7 S 3 level. The large population of ions in this latter level (up to 10% of all Fe ) can only be explained through ionization of Fe , as a large fraction of the ionized Fe  ions (we calculate 31% using the Flexible Atomic and Cowan codes) initially populate the 7 S 3 level of Fe  rather than the ground state. This channel for producing a significant Fe  7 S 3 level population may be relevant for other objects in which absorption lines from this level, the UV34 triplet, are observed, such as broad absorption line (BAL) quasars and η Carinae. This provides conclusive evidence for timevariable ionization in the circumburst medium, which to date has not been convincingly detected. However, the best-fit distance of the neutral absorbing cloud to the GRB is 200-400 pc, i.e. similar to GRB-absorber distance estimates for GRBs without any evidence for ionization. We find that the presence of time-varying ionization in GRB 080310 is likely due to a combination of the super-solar iron abundance ([Fe/H] = +0.2) and the low H  column density (log N(H ) = 18.7) in the host of GRB 080310. Finally, the modelling provides indications for the presence of an additional cloud at 10-50 pc from the GRB with log N(H ) ∼ 19-20 before the burst, which became fully ionized by the radiation released during the first few tens of minutes after the GRB.

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“…Given the very high column densities of gas regularly detected in GRB afterglow spectra (e.g., Jensen et al 2001;Hjorth et al 2003a;Vreeswijk et al 2004;Jakobsson et al 2006) and their direct link to star-formation (e.g., Galama et al 1998;Hjorth et al 2003b), this low detection rate of H 2 was initially quite surprising. Because the material probed by GRB-DLAs is in many cases located at distances of several hundred parsecs or more from the γ-ray burst (e.g., Vreeswijk et al 2007Vreeswijk et al , 2011D'Elia et al 2009;Sheffer et al 2009), the afterglow's UV flux itself will not photo-dissociate the H 2 of the GRB-DLA (e.g., Tumlinson et al 2007; Ledoux et al 2009). A genuine deficit of molecular hydrogen in GRB-DLAs as compared to QSO-DLAs for example, would instead indicate that H 2 is absent already prior to the burst.…”

Section: Introductionmentioning

confidence: 99%

Molecular hydrogen in the damped Lyman αsystem towards GRB 120815A atz= 2.36

Krühler

Ledoux

Fynbo

et al. 2013

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We present the discovery of molecular hydrogen (H 2 ), including the presence of vibrationally-excited H * 2 in the optical spectrum of the afterglow of GRB 120815A at z = 2.36 obtained with X-shooter at the VLT. Simultaneous photometric broad-band data from GROND and X-ray observations by Swift/XRT place further constraints on the amount and nature of dust along the sightline. The galactic environment of GRB 120815A is characterized by a strong DLA with log(N(H )/cm −2 ) = 21.95 ± 0.10, prominent H 2 absorption in the Lyman-Werner bands (log(N(H 2 )/cm −2 ) = 20.54 ± 0.13) and thus a molecular gas fraction log f (H 2 ) = −1.14 ± 0.15. The distance d between the absorbing neutral gas and GRB 120815A is constrained via photo-excitation modeling of fine-structure and meta-stable transitions of Fe  and Ni  to d = 0.5 ± 0.1 kpc. The DLA metallicity ([Zn/H] = −1.15 ± 0.12), visual extinction (A V < ∼ 0.15 mag) and dust depletion ([Zn/Fe] = 1.01 ± 0.10) are intermediate between the values of well-studied, H 2 -deficient GRB-DLAs observed at high spectral resolution, and the approximately solar metallicity, highly-obscured and H 2 -rich GRB 080607 sightline. With respect to N(H ), metallicity, as well as dust-extinction and depletion, GRB 120815A is fairly representative of the average properties of GRB-DLAs. This demonstrates that molecular hydrogen is present in at least a fraction of the more typical GRBDLAs, and H 2 and H * 2 are probably more wide-spread among GRB-selected systems than the few examples of previous detections would suggest. Because H * 2 transitions are located redwards of the Lyman α absorption, H * 2 opens a second route for positive searches for molecular absorption also in GRB afterglows at lower redshifts and observed at lower spectral resolution. Further detections of molecular gas in GRB-DLAs would allow statistical studies, and, coupled with host follow-up and sub-mm spectroscopy, provide unprecedented insights into the process and conditions of star-formation at high redshift.

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Rapid-response mode VLT/UVES spectroscopy of GRB 060418 (Corrigendum)

Cited by 18 publications

References 4 publications

The mysterious optical afterglow spectrum of GRB 140506A atz= 0.889

The mysterious optical afterglow spectrum of GRB 140506A atz= 0.889

Time-dependent excitation and ionization modelling of absorption-line variability due to GRB 080310

Molecular hydrogen in the damped Lyman αsystem towards GRB 120815A atz= 2.36

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