Hao 2006 GRB060206的铁镁吸收线

主要内容:


精彩摘抄:


文章信息:

astro-ph/0612409 [abs, ps, pdf, other] :

Title: Strongly Variable z=1.48 MgII and FeII Absorption in the Spectra of z=4.05 GRB 060206
Authors: H. Hao, K. Z. Stanek, A. Dobrzycki, T. Matheson, M. C. Bentz, J. Kuraszkiewicz, P. M. Garnavich, J. C. Howk, M. L. Calkins, G. Worthey, M. Modjaz, J. Serven
Comments: 14 pages, 4 figures, 1 table; ApJ Letters, submitted

We report on the discovery of strongly variable MgII and FeII absorption lines seen at z=1.48 in the spectra of the z=4.05 GRB 060206 obtained between 4.13 to 7.63 hours after the burst. In particular, the FeII line equivalent width (EW) decayed rapidly from 1.72+-0.25 AA to 0.28+-0.21 AA, only to increase to 0.96+-0.21 AA in a later date spectrum. The MgII doublet shows even more complicated evolution: the weaker line of the doublet drops from 2.05+-0.25 AA to 0.92+-0.32 AA, but then more than doubles to 2.47+-0.41 AA in later data. The ratio of the EWs for the MgII doublet is also variable, being closer to 1:1 (saturated regime) when the lines are stronger and becoming closer to 2:1 (unsaturated regime) when the lines are weaker, consistent with expectations based on atomic physics. We have investigated and rejected the possibility of any instrumental or atmospheric effects causing the observed strong variations. The possibility of variable intervening absorption in GRB spectra was recently predicted by Frank et al. (astro-ph/0605676). Our discovery of clearly variable intervening FeII and MgII lines lends very strong support to their scenario, in which the characteristic size of intervening patches of MgII ``clouds'' is comparable to the GRB beam size, i.e, about 10^16 cm. We discuss various implications of this discovery, including the nature of the MgII absorbers, the physics of GRBs, and measurements of chemical abundances from GRB and quasar absorption lines.