We present a carefully selected sub-sample of Swift long gamma-ray bursts (GRBs) that is complete in redshift. The sample is constructed by considering only bursts with favorable observing conditions for ground-based follow-up searches, which are bright in the 15-150?keV Swift/BAT band, i.e., with 1-s peak photon fluxes in excess to 2.6?photons?s–1?cm–2. The sample is composed of 58 bursts, 52 of them with redshift for a completeness level of 90%, while another two have a redshift constraint, reaching a completeness level of 95%. For only three bursts we have no constraint on the redshift. The high level of redshift completeness allows us for the first time to constrain the GRB luminosity function and its evolution with cosmic times in an unbiased way. We find that strong evolution in luminosity (δ l = 2.3 ± 0.6) or in density (δ d = 1.7 ± 0.5) is required in order to account for the observations. The derived redshift distributions in the two scenarios are consistent with each other, in spite of their different intrinsic redshift distributions. This calls for other indicators to distinguish among different evolution models. Complete samples are at the base of any population studies. In future works we will use this unique sample of Swift bright GRBs to study the properties of the population of long GRBs.
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机译：我们提出了经过精心选择的快速长伽马射线暴（GRB）子样本，该子样本已完成红移。该样本是通过仅考虑具有良好观察条件的猝发来构造的，以便进行地面后续跟踪，这些猝发在15-150？keV Swift / BAT波段明亮，即1-s峰值光子通量超过2.6?。光子？s–1？cm–2。该样本由58个脉冲组成，其中52个具有红移，其完整性等级为90％，而另外两个具有红移约束，达到了95％的完整性等级。对于只有三个脉冲，我们对红移没有任何限制。高级别的红移完整性使我们第一次可以无偏地限制GRB的光度函数及其随宇宙时间的演化。我们发现，需要考虑光度（δl = 2.3±0.6）或密度（δd = 1.7±0.5）的强烈演化，以便说明观测结果。尽管它们的固有红移分布不同，但在两种情况下派生的红移分布彼此一致。这就需要其他指标来区分不同的演化模型。完整的样本是任何人口研究的基础。在以后的工作中，我们将使用Swift明亮GRB的唯一样本来研究长GRB的种群属性。
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