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No Evidence for Variability of Intervening Absorption Lines toward GRB 060206: Implications for the Mg ii Incidence Problem

2009; Oxford University Press; Volume: 61; Issue: 2 Linguagem: Inglês

10.1093/pasj/61.2.387

2053-051X

Kentaro Aoki, Tomonori Totani, Takashi Hattori, Kouji Ohta, Koji S. Kawabata, Naoto Kobayashi, Masanori Iye, K. Nomoto, N. Kawai,

Astrophysical Phenomena and Observations

Abstract We examined the variability of absorption line strength of intervening systems along the line of sight to GRB 060206 at z$=$ 4.05, utilizing low-resolution optical spectra obtained by the Subaru telescope from six to ten hours after the burst. Strong variabilities of Fe ii and Mg ii lines at z$=$ 1.48 during $t$$=$ 5–8 hr have been reported for this GRB, and those have been used to support the idea of clumpy Mg ii cloudlets, which was originally proposed to explain the anomalously high incidence of Mg ii absorbers in the GRB spectra compared to quasars. However, our spectra with a higher signal-to-noise ratio do not show any evidence for variability in $t$$=$ 6–10 hr. There is a clear discrepancy between our data and those of Hao et al. (2007, ApJ, 659, L99) in the overlapping time interval. Furthermore, the line strengths in our data are in agreement with those observed at $t$$\sim$ 2 hr by Thöne et al. (2008, A&A, 489, 37). We also detected Fe ii and Mg ii absorption lines for a system at z$=$ 2.26; these lines do not show evidence for variability either. Therefore, we conclude that there is no strong evidence for the variability in the intervening absorption lines toward GRB 060206, offering poor support for the Mg ii cloudlet hypothesis by the GRB 060206 data.