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arXiv 0809.1559astro-ph
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z > 2时伽马射线暴余辉的鲁棒测光红移测定

Robust photometric redshift determinations of gamma-ray burst afterglows at z > 2

P. A. Curran, R. A. M. J. Wijers, M. H. M. Heemskerk, R. L. C. Starling, K. Wiersema, A. J. van der Horst

摘要:

理论认为,大约10%的雨燕探测到的伽马射线暴(GRB)将起源于大于5的红移,但由于缺乏测量的红移,一些高红移的候选者可能无法确认。在这里,我们介绍我们的代码,GRBz,同时多参数拟合的伽玛暴余辉光学和近红外光谱能量分布的方法。它允许早期测定的光度红移,光谱指数和主机消光。我们假设伽玛射线暴余辉光谱是很好地代表了幂律衰减和模型的吸收,由于莱曼森林和主机灭绝的影响。我们使用基于遗传算法的例程,同时适合感兴趣的参数,和蒙特卡洛误差分析。我们使用以前确定的光谱红移的伽玛暴来证明我们的方法,同时还介绍了新的近红外数据的伽玛暴990510,进一步限制主机消光值。我们的方法是有效的,在估计的光度红移的伽玛暴,相对无偏的余辉光谱指数或宿主星系灭绝的假设。由于基于遗传算法最优种群的误差估计方法大大低估了误差,因此需要进行蒙特卡罗误差分析。

英文摘要:

Theory suggests that about 10% of Swift-detected gamma-ray bursts (GRBs) will originate at redshifts greater than 5 yet a number of high redshift candidates may be left unconfirmed due to the lack of measured redshifts. Here we introduce our code, GRBz, a method of simultaneous multi-parameter fitting of GRB afterglow optical and near infrared, spectral energy distributions. It allows for early determinations of the photometric redshift, spectral index and host extinction to be made. We assume that GRB afterglow spectra are well represented by a power-law decay and model the effects of absorption due to the Lyman forest and host extinction. We use a genetic algorithm-based routine to simultaneously fit the parameters of interest, and a Monte Carlo error analysis. We use GRBs of previously determined spectroscopic redshifts to prove our method, while also introducing new near infrared data of GRB 990510 which further constrains the value of the host extinction. Our method is effective in estimating the photometric redshift of GRBs, relatively unbiased by assumptions of the afterglow spectral index or the host galaxy extinction. Monte Carlo error analysis is required as the method of error estimate based on the optimum population of the genetic algorithm underestimates errors significantly.

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