LOW-RESOLUTION SPECTROSCOPY OF GAMMA-RAY BURST OPTICAL AFTERGLOWS: BIASES IN THE
                    <i>SWIFT</i>
                    SAMPLE AND CHARACTERIZATION OF THE ABSORBERS

Fynbo, J. P. U.; Jakobsson, P.; Prochaska, J. Xavier; Malesani, D.; Ledoux, C.; Postigo, A. de Ugarte; Nardini, M.; Vreeswijk, P. M.; Wiersema, K.; Hjorth, J.; Sollerman, J.; Chen, Hsiao‐Wen; Thöne, C. C.; Björnsson, G.; Bloom, J.; Castro-Tirado, A. J.; Christensen, L.; De, A.; Fruchter, A. S.; Gorosabel, J.; Graham, John F.; Jaunsen, A. O.; Jensen, B. L.; Канн, Д. А.; Kouveliotou, C.; Levan, A. J.; Maund, Justyn R.; Masetti, N.; Milvang-Jensen, B.; Palazzi, E.; Perley, D.; Pian, E.; Rol, E.; Schady, P.; Starling, R. L. C.; Tanvir, N. R.; Watson, Derrick G.; Xu, D.; Augusteijn, T.; Grundahl, F.; Telting, J. H.; Quirion, Pierre-Olivier

doi:10.1088/0067-0049/185/2/526

Cited by 326 publications

(328 citation statements)

References 122 publications

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“…Gas-to-dust and metal-to-dust ratios for GRB 100219A are high as it is generally the case for GRBs, (Watson & Jakobsson, 2012), above the values for the local group Zafar et al 2011. This is usually explained by ionization of HI and in particular dust destruction by the GRB (Watson et al, 2007;Campana et al, 2009;Fynbo et al, 2009). This could also explain the very large difference between optical and X-ray column densities (about a factor of 10), as generally found for GRBs, since X-ray absorption is not affected by ionization and hence most metals are found in highly ionized states due to the absence of a large column density of moderately ionized metals (Schady et al, 2011).…”

Section: Sed From X-ray To Irmentioning

confidence: 81%

GRB 100219A with X-shooter – abundances in a galaxy at z =4.7

Thöne¹,

Fynbo²,

Goldoni³

et al. 2012

Monthly Notices of the Royal Astronomical Society

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Context. Abundances of galaxies at redshifts z > 4 are difficult to obtain from damped Ly α (DLA) systems in the sightlines of quasars (QSOs) due to the Ly α forest blanketing and the low number of high-redshift quasars detected. Gamma-ray bursts (GRBs) with their higher luminosity are well suited to study galaxies out to the formation of the first stars at z > 10. Its large wavelength coverage makes the X-shooter spectrograph an excellent tool to study the interstellar medium (ISM) of high redshift galaxies, in particular if the redshift is not known beforehand. Aims. We want to determine the properties of a GRB host at z = 4.66723 from absorption lines. This is one of the highest redshifts where a detailed analysis with medium-resolution data is possible. Furthermore, we determine the dust extinction using the spectral energy distribution from X-rays to near infrared. Finally, we put the results in context to other GRBs at z > 4 and properties of (high redshift) QSO absorbers. Methods. The velocity components of the resonant and fine-structure absorption lines are fitted with Voigt-profiles and the metallicity determined from S, Si, Fe and O. Si II* together with the energy released in the UV restframe as determined from GROND photometric data gives us the distance of the absorbing material from the GRB. The extinction is determined from the spectral slope using X-ray spectral information and the flux calibrated X-shooter spectrum, cross calibrated with photometric data from GROND. We also collect information on all GRB hosts with z > 4. Results. We measure a relatively high metallicity of [M/H] = −1.0 ± 0.1 from S, the distance of the material showing fine-structure lines is 0.3 to 1.0 kpc. The extinction is moderate with A V = 0.24 ± 0.06 mag. Low-and high ionization as well as fine-structure lines show a complicated kinematic structure probably pointing to a merger in progress. We detect one intervening system at z = 2.18. Conclusions. GRB-DLAs have a shallower evolution of metallicity with redshift than QSO absorbers and no evolution in their HI column density or ionization fraction. GRB hosts at high redshift seem to continue the trend of the metallicity-luminosity relation towards lower metallicities but the sample is still too small to draw a definite conclusion. While the detection of GRBs at z > 4 with current satellites is still difficult, they are very important for our understanding of the early epochs of star-and galaxy-formation in the Universe.

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Section: Sed From X-ray To Irmentioning

confidence: 81%

GRB 100219A with X-shooter – abundances in a galaxy at z =4.7

Thöne¹,

Fynbo²,

Goldoni³

et al. 2012

Monthly Notices of the Royal Astronomical Society

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“…All numbers are normalized to the total number of triggered events. The triggered events from our simulation are plotted in red; the selected Swift GRBs sample (Fynbo et al 2009) is plotted in blue for comparison. Figure 1 shows our preliminary results based on the GRB characteristics discussed above.…”

Section: Introduction and Methodsmentioning

confidence: 99%

“…Note that this Swift-detected GRB sample is a sub-sample of all GRBs observed by Swift. This sub-sample is selected by Fynbo et al (2009), using criteria for choosing GRBs that produce an event sample that is relatively unaffected by selection biases in redshift measurements.…”

Section: Introduction and Methodsmentioning

confidence: 99%

Trigger Simulations for GRB Detection with the Swift Burst Alert Telescope

et al. 2011

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Abstract. Understanding the intrinsic cosmic long gamma-ray burst (GRB) rate is essential in many aspects of astrophysics and cosmology, such as revealing the connection between GRBs, supernovae (SNe), and stellar evolution. Swift, a multi-wavelength space telescope, is quickly expanding the GRB category by observing hundreds of GRBs and their redshifts. However, it remains difficult to determine the intrinsic GRB rate due to the complex trigger algorithm adopted by Swift. Current studies of the GRB rate usually approximate the Swift trigger algorithm by a single detection threshold. Nevertheless, unlike the previously flown GRB instruments, Swift has over 500 trigger criteria based on count rates and additional thresholds for localization. To investigate possible systematic biases and further explore the intrinsic GRB rate as a function of redshift and the GRB luminosity function, we adopt a Monte Carlo approach by simulating all trigger criteria used by Swift. A precise estimation of the intrinsic GRB rate is important to reveal the GRB origins and their relation to the black-hole forming SNe. Additionally, the GRB rate at high redshifts provides a strong probe of the star formation history in the early universe, which is hard to measure directly through other methods.

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“…Some of the more widely understood effects are discussed by Fynbo et al [1] in detail. Optical biases have reduced the fraction of Swift triggered OAs, and have introduced a selection towards detecting the brightest OAs, hence the more nearby bursts.…”

Section: Grb Optical Selection Effectsmentioning

confidence: 99%

“…The host galaxies are usually too faint to make a significant contribution to the spectra. Most GRB spectroscopic redshifts are acquired by large aperture ground based telescopes, including VLT, Gemini-S-N, Keck and Lick (see [1] for a more complete list along with specific spectroscopy instruments). The measurement of a GRB redshift depends strongly on the limiting sensitivity and spectral coverage of the spectroscopic system.…”

Section: Redshift Desertmentioning

confidence: 99%

The mystery of the missing GRB redshifts

Coward¹,

Howell²,

Branchesi³

et al. 2012

Proceedings of Gamma-Ray Bursts 2012 Conference — PoS(GRB 2012)

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It is clear that optical selection effects have distorted the "true" GRB redshift distribution to its presently observed biased distribution. We a statistically optimal model that implies GRB host galaxy dust extinction could account for up to 40% of missing optical afterglows and redshifts in z = 0 − 3, but the bias is negligible at very high-z. The limiting sensitivity of the telescopes, and the time to acquire spectroscopic/photometric redshifts, are significant sources of bias for the very high-z sample. We caution on constraining star formation rate and luminosity evolution using the GRB redshift distribution without accounting for these selection effects.

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LOW-RESOLUTION SPECTROSCOPY OF GAMMA-RAY BURST OPTICAL AFTERGLOWS: BIASES IN THE SWIFT SAMPLE AND CHARACTERIZATION OF THE ABSORBERS

Cited by 326 publications

References 122 publications

GRB 100219A with X-shooter – abundances in a galaxy at z =4.7

GRB 100219A with X-shooter – abundances in a galaxy at z =4.7

Trigger Simulations for GRB Detection with the Swift Burst Alert Telescope

The mystery of the missing GRB redshifts

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