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An Independent Measurement of the Incidence of Mg II Absorbers along Gamma-Ray Burst Sight Lines: The End of the Mystery?

Cucchiara, A. and Prochaska, J. X. and Zhu, G.. and Ménard, B. and Fynbo, J. P. U. and Fox, D. B. and Chen, H.-W. and Cooksey, K. L. and Cenko, S. B. and Perley, D. and Bloom, J. S. and Berger, E. and Tanvir, N. R. and D'Elia, V. and Lopez, S. and Chornock, R. and de Jaeger, T. (2013) An Independent Measurement of the Incidence of Mg II Absorbers along Gamma-Ray Burst Sight Lines: The End of the Mystery? Astrophysical Journal, 773 (2). Art. No. 82. ISSN 0004-637X. doi:10.1088/0004-637X/773/2/82.

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In 2006, Prochter et al. reported a statistically significant enhancement of very strong Mg ii absorption systems intervening the sight lines to gamma-ray bursts (GRBs) relative to the incidence of such absorption along quasar sight lines. This counterintuitive result has inspired a diverse set of astrophysical explanations (e.g., dust, gravitational lensing) but none of these has obviously resolved the puzzle. Using the largest set of GRB afterglow spectra available, we reexamine the purported enhancement. In an independent sample of GRB spectra with a survey path three times larger than Prochter et al., we measure the incidence per unit redshift of ≥1 Å rest-frame equivalent width Mg ii absorbers at z ≈ 1 to be ℓ(z) = 0.18 ± 0.06. This is fully consistent with current estimates for the incidence of such absorbers along quasar sight lines. Therefore, we do not confirm the original enhancement and suggest those results suffered from a statistical fluke. Signatures of the original result do remain in our full sample (ℓ(z) shows an ≈1.5 enhancement over ℓ(z)_(QSO)), but the statistical significance now lies at ≈90% c.l. Restricting our analysis to the subset of high-resolution spectra of GRB afterglows (which overlaps substantially with Prochter et al.), we still reproduce a statistically significant enhancement of Mg ii absorption. The reason for this excess, if real, is still unclear since there is no connection between the rapid afterglow follow-up process with echelle (or echellette) spectrographs and the detectability of strong Mg ii doublets. Only a larger sample of such high-resolution data will shed some light on this matter.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Prochaska, J. X.0000-0002-7738-6875
Fynbo, J. P. U.0000-0002-8149-8298
Fox, D. B.0000-0002-3714-672X
Cenko, S. B.0000-0003-1673-970X
Perley, D.0000-0001-8472-1996
Bloom, J. S.0000-0002-7777-216X
Berger, E.0000-0002-9392-9681
Chornock, R.0000-0002-7706-5668
de Jaeger, T.0000-0001-6069-1139
Additional Information:© 2013 American Astronomical Society. Received 2012 November 27; accepted 2013 May 25; published 2013 July 29. A.C. thanks the anonymous referee for the valuable comments and suggestions. A.C. also thanks J.X. Prochaska for the fundamental guidances, without which this work could not be possible. A.C. also thanks B. Menard and B. Zhu for the useful comments and to have provided the best to date compilation of high signal-to-noise quasars spectra as well their Mgii search results. Gemini results are based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Ministerio de Ciencia, Tecnología e Innovaciόn Productiva (Argentina). S.L. has been supported by FONDECYT grant number 1100214 and received partial support from the Center of Excellence in Astrophysics and Associated Technologies (PFB 06). J.P.U.F. acknowledges support from the ERC-StG grant EGGS-278202. The Dark Cosmology Centre is funded by the DNRF.
Funding AgencyGrant Number
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1100214
Center for Astrophysics and Associated Technologies (CATA)PFB 06
European Research Council (ERC)EGGS-278202
Danish National Research FoundationUNSPECIFIED
Subject Keywords:gamma-ray burst: general; quasars: absorption lines; techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20130920-133053054
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Official Citation:An Independent Measurement of the Incidence of Mg II Absorbers along Gamma-Ray Burst Sight Lines: The End of the Mystery? A. Cucchiara, J. X. Prochaska, G. Zhu, B. Ménard, J. P. U. Fynbo, D. B. Fox, H.-W. Chen, K. L. Cooksey, S. B. Cenko, D. Perley, J. S. Bloom, E. Berger, N. R. Tanvir, V. D'Elia, S. Lopez, R. Chornock, and T. de Jaeger
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41449
Deposited By: Ruth Sustaita
Deposited On:20 Sep 2013 21:21
Last Modified:10 Nov 2021 04:30

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