主要内容:
从而得到一些元素丰度。
从余辉拐折时间推出喷流角度，然后得到E_gamma<3.5e52erg,说可能是能量最高的一个暴。
精彩摘抄:
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| 谱 |
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| 光变 |
文章信息:
- · arXiv e-print (arXiv:1004.3261)
- · References in the Article
- · Citations to the Article (4) (Citation History)
- · Refereed Citations to the Article
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| Title: |
| A very metal poor Damped Lyman-alpha system revealed through the most energetic GRB 090926A |
| Authors: |
| Rau, Arne; Savaglio, S.; Krühler, T.; Afonso, P.; Greiner, J.; Klose, S.; Schady, P.; McBreen, S.; Filgas, R.; Olivares E., F.; Rossi, A.; Updike, A. |
| Publication: |
| eprint arXiv:1004.3261 |
| Publication Date: |
| 04/2010 |
| Origin: |
| ARXIV |
| Keywords: |
| Astrophysics - Cosmology and Extragalactic Astrophysics |
| Comment: |
| ApJ accepted for submission, revised for referee comments, 11 pages, 7 figures |
| Bibliographic Code: |
| 2010arXiv1004.3261R |
Abstract
We present VLT/FORS2 spectroscopy and GROND optical/near-IR photometry of the afterglow of the bright Fermi/LAT GRB 090926A. The spectrum shows prominent Lyman-alpha absorption with N_HI = 10^(21.73 +/- 0.07) cm^-2 and a multitude of metal lines at a common redshift of z=2.1062 +/- 0.0004, which we associate with the redshift of the GRB. The metallicity derived from SII is log(Z/Z_sun) ~ -1.9, one of the lowest values ever found in a GRB Damped Lyman-alpha (DLA) system. This confirms that the spread of metallicity in GRB-DLAs at z~2 is at least two orders of magnitude. We argue that this spread in metallicity does not require a similar range in abundances of the GRB progenitors, since the neutral interstellar medium probed by the DLA is expected to be at a significant distance from the explosion site. The hydrogen column density derived from Swift/XRT afterglow spectrum (assuming log(Z/Z_sun) ~ -1.9) is approx. 100 times higher than the N_HI obtained from the Lyman-alpha absorptions. This suggests either a large column density of ionized gas or a higher metallicity of the circum-burst medium compared to the gas traced by the DLA. We also discuss the afterglow light curve evolution and energetics. The absence of a clear jet-break like steeping until at least 21 days post-burst suggests a beaming corrected energy release of E_gamma>3.5x10^52erg, indicating that GRB090926A may have been one of the most energetic bursts ever detected.
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