Low-resolution Spectroscopy of Gamma-ray Burst Optical Afterglows: Biases in the Swift Sample and Characterization of the Absorbers
Johan P. U. Fynbo,Johan P. U. Fynbo,Pall Jakobsson,Jason X. Prochaska,D. Malesani,C. Ledoux,A. de Ugarte Postigo,Marco Nardini,P. M. Vreeswijk,P. M. Vreeswijk,Klaas Wiersema,Jens Hjorth,Jesper Sollerman,Jesper Sollerman,Hsiao-Wen Chen,Christina C. Thöne,Christina C. Thöne,Gunnlaugur Björnsson,Joshua S. Bloom,A. J. Castro-Tirado,Lise Christensen,A. De Cia,A. S. Fruchter,Javier Gorosabel,John F. Graham,Andreas O. Jaunsen,Andreas O. Jaunsen,B. L. Jensen,D. A. Kann,Chryssa Kouveliotou,Andrew J. Levan,Justyn R. Maund,N. Masetti,Bo Milvang-Jensen,Eliana Palazzi,Daniel A. Perley,Elena Pian,Evert Rol,Patricia Schady,R. L. C. Starling,Nial R. Tanvir,Darach Watson,Dong Xu,T. Augusteijn,Frank Grundahl,J. H. Telting,P. O. Quirion +46 more
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In this article, the authors presented a sample of 77 optical afterglows (OAs) of Swift detected gamma-ray bursts (GRBs) for which spectroscopic follow-up observations have been secured.Abstract:
We present a sample of 77 optical afterglows (OAs) of Swift detected gamma-ray bursts (GRBs) for which spectroscopic follow-up observations have been secured. Our first objective is to measure the redshifts of the bursts. For the majority (90%) of the afterglows, the redshifts have been determined from the spectra. We provide line lists and equivalent widths (EWs) for all detected lines redward of Lyα covered by the spectra. In addition to the GRB absorption systems, these lists include line strengths for a total of 33 intervening absorption systems. We discuss to what extent the current sample of Swift bursts with OA spectroscopy is a biased subsample of all Swift detected GRBs. For that purpose we define an X-ray-selected statistical sample of Swift bursts with optimal conditions for ground-based follow-up from the period 2005 March to 2008 September; 146 bursts fulfill our sample criteria. We derive the redshift distribution for the statistical (X-ray selected) sample and conclude that less than 18% of Swift bursts can be at z > 7. We compare the high-energy properties (e.g., γ-ray (15-350 keV) fluence and duration, X-ray flux, and excess absorption) for three subsamples of bursts in the statistical sample: (1) bursts with redshifts measured from OA spectroscopy; (2) bursts with detected optical and/or near-IR afterglow, but no afterglow-based redshift; and (3) bursts with no detection of the OA. The bursts in group (1) have slightly higher γ-ray fluences and higher X-ray fluxes and significantly less excess X-ray absorption than bursts in the other two groups. In addition, the fractions of dark bursts, defined as bursts with an optical to X-ray slope βOX 39% in group (3). For the full sample, the dark burst fraction is constrained to be in the range 25%-42%. From this we conclude that the sample of GRBs with OA spectroscopy is not representative for all Swift bursts, most likely due to a bias against the most dusty sight lines. This should be taken into account when determining, e.g., the redshift or metallicity distribution of GRBs and when using GRBs as a probe of star formation. Finally, we characterize GRB absorption systems as a class and compare them to QSO absorption systems, in particular the damped Lyα absorbers (DLAs). On average GRB absorbers are characterized by significantly stronger EWs for H I as well as for both low and high ionization metal lines than what is seen in intervening QSO absorbers. However, the distribution of line strengths is very broad and several GRB absorbers have lines with EWs well within the range spanned by QSO-DLAs. Based on the 33 z > 2 bursts in the sample, we place a 95% confidence upper limit of 7.5% on the mean escape fraction of ionizing photons from star-forming galaxies. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under programs 275.D-5022 (PI: Chincarini), 075.D-0270 (PI: Fynbo), 077.D-0661 (PI: Vreeswijk), 077.D-0805 (PI: Tagliaferri), 177.A-0591 (PI: Hjorth), 078.D-0416 (PI: Vreeswijk), 079.D-0429 (PI: Vreeswijk), 080.D-0526 (PI: Vreeswijk), 081.A-0135 (PI: Greiner), 281.D-5002 (PI: Della Valle), and 081.A-0856 (PI: Vreeswijk). Also based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Some of the data obtained herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck foundation.read more
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A γ-ray burst at a redshift of z ≈ 8.2
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The Afterglows of Swift-era Gamma-ray Bursts. I. Comparing pre-Swift and Swift-era Long/Soft (Type II) GRB Optical Afterglows
David Alexander Kann,Sylvio Klose,Bing Zhang,D. B. Malesani,Ehud Nakar,Ehud Nakar,A. Pozanenko,A. C. Wilson,Nathaniel R. Butler,Pall Jakobsson,Pall Jakobsson,Steve Schulze,Maksim V. Andreev,L. A. Antonelli,I. F. Bikmaev,V. Biryukov,Markus Böttcher,R. A. Burenin,J. M. Castro Cerón,J. M. Castro Cerón,A. J. Castro-Tirado,G. Chincarini,G. Chincarini,B. E. Cobb,B. E. Cobb,Stefano Covino,P. D'Avanzo,Valerio D'Elia,M. Della Valle,M. Della Valle,A. de Ugarte Postigo,Yu. S. Efimov,P. Ferrero,Dino Fugazza,Johan P. U. Fynbo,M. Gålfalk,F. Grundahl,Javier Gorosabel,S. Gupta,Sergei Guziy,B. M. Hafizov,Jens Hjorth,K. Holhjem,Mansur Ibrahimov,Myungshin Im,G. L. Israel,M. Jeĺinek,B. L. Jensen,R. Karimov,Irek Khamitov,Ü. Kızıloǧlu,E. Klunko,Petr Kubánek,Alexander Kutyrev,Peter Laursen,Andrew J. Levan,Filippo Mannucci,C. M. Martin,A. Mescheryakov,Nestor Mirabal,Jay P. Norris,J. E. Ovaldsen,D. Paraficz,Elena P. Pavlenko,Silvia Piranomonte,Andrea Rossi,Vasilij Rumyantsev,R. Salinas,A. Sergeev,D. Sharapov,Jesper Sollerman,Jesper Sollerman,Bringfried Stecklum,Luigi Stella,Gianpiero Tagliaferri,Nial R. Tanvir,J. Telting,Vincenzo Testa,Adria C. Updike,A. Volnova,Darach Watson,Klaas Wiersema,Klaas Wiersema,Dong Xu +83 more
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The luminosity function and the rate of Swift's Gamma Ray Bursts
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TL;DR: The second Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts (GRBs) as mentioned in this paper contains 476 bursts detected by the BAT between 2004 December 19 and 2009 December 21.
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TL;DR: In this article, a carefully selected sub-sample of Swift Long Gamma-ray Bursts (GRBs) that is complete in redshift was constructed by considering only bursts with favorable observing conditions for ground-based follow-up searches, that are bright in the 15-150 keV Swift/BAT band, with 1-s peak photon fluxes in excess to 2.6 ph s^-1 cm^-2.
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TL;DR: In this paper, the duration distribution of the gamma-ray bursts of the first BATSE catalog is studied and a bimodality in the distribution is found, which separates GRBs into two classes: short events (less than 2 s) and longer ones (more than 2 S).
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