低亮度伽马射线暴作为一个独特的GRB人口：一个更坚定的情况下，从多准则约束
Low-Luminosity Gamma-Ray Bursts as a Distinct GRB Population:A Firmer Case from Multiple Criteria Constraints
摘要：
Swift/BAT X射线闪光XRF 060218和BATSE-BeppoSAX伽马射线暴GRB 980425的有趣观测，与其他观测到的暴相比，它们的亮度和红移都要低得多，这自然会导致这些低亮度（LL）暴与高亮度（HL）暴如何相关的问题。在CGRO/BATSE和Swift/BAT观测到的限流样本和已知红移的GRB样本的约束条件下，我们通过模拟研究了LL-和HL-GRB的光度函数。我们的多个标准，包括来自通量限制的GRB样品的log N-log P分布，红移已知样品的红移和光度分布，以及使用Swift/BAT对HL-和LL-GRB的探测率，提供了一组严格的约束条件。假设伽玛暴速率遵循恒星形成速率，我们的模拟表明，一个简单的幂律或破坏幂律模型的光度函数无法重现的意见，和一个新的组件是必需的。这个分量可以用一个破断功率来建模，其特征是在L < 10^47 erg s^-1}附近爆发数急剧增加。在红移~0.3处没有探测到中等亮度的伽玛暴，表明这一特征不是由于观测偏差造成的。从我们的模型中推断出，在~ 10^47 erg s^-1时，LL-GRB的局部速率rho_0为~ 200 Gpc^-3 yr^-1，远大于HL-GRB。这些结果意味着LL-GRB可能是与HL-GRB不同的GRB种群。最近发现的本地X射线瞬态080109/SN 2008 D将加强我们的结论，如果所观察到的非热发射有一个类似的起源，作为大多数伽玛暴和XRF的即时发射。
英文摘要：
The intriguing observations of Swift/BAT X-ray flash XRF 060218 and the BATSE-BeppoSAX gamma-ray burst GRB 980425, both with much lower luminosity and redshift compared to other observed bursts, naturally lead to the question of how these low-luminosity (LL) bursts are related to high-luminosity (HL) bursts. Incorporating the constraints from both the flux-limited samples observed with CGRO/BATSE and Swift/BAT and the redshift-known GRB sample, we investigate the luminosity function for both LL- and HL-GRBs through simulations. Our multiple criteria, including the log N - log P distributions from the flux-limited GRB sample, the redshift and luminosity distributions of the redshift-known sample, and the detection ratio of HL- and LL- GRBs with Swift/BAT, provide a set of stringent constraints to the luminosity function. Assuming that the GRB rate follows the star formation rate, our simulations show that a simple power law or a broken power law model of luminosity function fail to reproduce the observations, and a new component is required. This component can be modeled with a broken power, which is characterized by a sharp increase of the burst number at around L < 10^47 erg s^-1}. The lack of detection of moderate-luminosity GRBs at redshift ~0.3 indicates that this feature is not due to observational biases. The inferred local rate, rho_0, of LL-GRBs from our model is ~ 200 Gpc^-3 yr^-1 at ~ 10^47 erg s^-1, much larger than that of HL-GRBs. These results imply that LL-GRBs could be a separate GRB population from HL-GRBs. The recent discovery of a local X-ray transient 080109/SN 2008D would strengthen our conclusion, if the observed non-thermal emission has a similar origin as the prompt emission of most GRBs and XRFs.
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