[论文解读] Gamma-Ray Bursts as Cosmological Tools

V. Petrosian, Aurelien Bouvier+1 more|ArXiv.org|Sep 28, 2009

Gamma-ray bursts and supernovae被引用 7

一句话总结

本文研究了伽马射线暴（GRBs）作为宇宙学距离指示器的使用，挑战了其作为标准烛光或遵循紧密关系（如Amati或Ghirlanda关系）的假设。研究发现GRBs存在显著的光度与谱演化证据，削弱了基于这些关系的当前宇宙学检验，结论是若不考虑复杂的演化效应和选择偏差，GRBs尚不足以作为可靠的宇宙学工具。

ABSTRACT

In recent years there has been considerable activity in using gamma-ray bursts as cosmological probes for determining global cosmological parameters complementing results from type Ia supernovae and other methods. This requires a characteristics of the source to be a standard candle. We show that contrary to earlier indications the accumulated data speak against this possibility. Another method would be to use correlation between a distance dependent and a distance independent variable to measure distance and determine cosmological parameters as is done using Cepheid variables and to some extent Type Ia supernovae. Many papers have dealt with the use of so called Amati relation, first predicted by Lloyd, Petrosian and Mallozzi, or the Ghirlanda relation for this purpose. We have argued that these procedure involve many unjustified assumptions which if not true could invalidate the results. In particular, we point out that many evolutionary effects can affect the final outcome. In particular, we demonstrate that the existing data from Swift and other earlier satellites show that the gamma-ray burst may have undergone luminosity evolution. Similar evolution may be present for other variables such as the peak photon energy of the total radiated energy. Another out come of our analysis is determination of the luminosity function and the comoving rate evolution of gamma-ray bursts which does not seem to agree with the cosmic star formation rate. We caution however, that the above result are preliminary and includes primarily the effect of detection threshold. Other selection effects, perhaps less important than this, are also known to be present and must be accounted for. We intend to address these issues in future publications.

研究动机与目标

• 利用标准烛光（SC）或基于相关性的方法，评估伽马射线暴（GRBs）作为宇宙学距离指示器的可行性。
• 调查观测到的Amati或Ghirlanda关系是否能可靠地确定宇宙学参数。
• 评估光度与谱演化对基于GRB的宇宙学检验的影响。
• 分析GRBs的共动率演化，并与宇宙恒星形成率（SFR）进行比较。
• 识别可能使当前基于GRB数据的宇宙学推断失效的选择效应与偏差。

提出的方法

• 分析具有已知红移的Swift时代及Swift之前时代的GRB数据，以评估各向同性能量（E_iso）和束流修正能量（E_gamma）的分布。
• 应用Efron & Petrosian（1992, 1994, 1999）的统计方法，对光度与能量分布中的探测阈值和右删失数据进行校正。
• 利用式（2）通过喷流转折时间与洛伦兹因子估算喷流张角，该式依赖于t_break、E_iso、n和红移。
• 构建GRB的光度函数与率演化模型，将其与不同红红移区间的宇宙恒星形成率（SFR）进行比较。
• 在演化假设与选择偏差下，评估E_p–E_iso与E_p–E_gamma相关性的稳健性。
• 对高光度与低光度GRB子样本进行对比分析，以评估其对率演化贡献。

实验结果

研究问题

• RQ1 伽马射线暴是否在本征光度上表现出足够的同质性，可被视为标准烛光？
• RQ2 在不考虑演化效应的情况下，Amati或Ghirlanda关系能否可靠地用于确定宇宙学参数？
• RQ3 GRBs中的光度与谱演化性质及其程度为何？其对宇宙学推断有何影响？
• RQ4 GRBs的共动率演化与宇宙恒星形成率（SFR）相比如何？这对GRB前身体意味着什么？
• RQ5 选择效应，尤其是探测阈值，多大程度上偏差了当前基于GRB的宇宙学结果？

主要发现

• Swift及更早卫星的数据表明，伽马射线暴存在强烈的光度演化证据，表明E_iso与E_gamma随宇宙时间并非恒定。
• GRBs中各向同性能量（E_iso）与束流修正能量（E_gamma）的分布具有显著离散性，排除其作为标准烛光的适用性。
• 观测到的GRB共动率演化与宇宙恒星形成率（SFR）不匹配，表明其前身体或演化机制可能不同。
• 高光度GRB子样本在低红移时对率的贡献较小，但即使在子样本分析后，整体率演化趋势仍与SFR不一致。
• E_p–E_iso相关性可能随时间演化，如Lei等人所建议，进一步削弱了当前宇宙学检验的可靠性。
• 选择效应，尤其是探测阈值，显著影响观测样本，未来统计模型必须考虑其他偏差。