We present the result of a search for orphan Gamma-Ray Burst (GRB) afterglows in the Pan-STARRS1 (PS1) COSMOS survey. There is extensive theoretical and observational evidence suggesting that GRBs are collimated jets; the direct observation of orphan GRB afterglows would further support this model. An optimal survey strategy is designed by coupling the PS1 survey with the Subaru/Hyper-Suprime-Cam (HSC) survey. The PS1 COSMOS survey, one of the survey fields in the PS1 Medium Deep Survey (PS1/MDS), searches a field of 7 deg$^2$ from December 2011 to January 2014, reaching a limiting magnitude R $\sim$ 23. The dense cadence of PS1/MDS is crucial for identifying transients, and the deep magnitude reached by the HSC survey (R $\sim$ 26) is important for evaluating potential GRB hosts. A transient classification method is employed to select potential orphan GRB afterglow candidates. After a thorough analysis of the transient and host galaxy properties, we conclude that there are no candidates in this survey field. The null result implies that the consideration of jet structures is essential for further orphan GRB afterglow surveys.

中文翻译：

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使用 Pan-STARRS1 COSMOS 巡天搜索孤儿 GRB 余辉

我们展示了在 Pan-STARRS1 (PS1) COSMOS 调查中搜索孤儿伽玛射线爆发 (GRB) 余辉的结果。大量的理论和观测证据表明 GRB 是准直射流；对孤儿 GRB 余辉的直接观察将进一步支持该模型。通过将 PS1 调查与 Subaru/Hyper-Suprime-Cam (HSC) 调查相结合来设计最佳调查策略。PS1 COSMOS 巡天是 PS1 中等深度巡天 (PS1/MDS) 中的巡天场之一，从 2011 年 12 月至 2014 年 1 月搜索 7 deg$^2$ 的场，达到极限星等 R$\sim$23。 PS1/MDS 的密集节奏对于识别瞬变至关重要，HSC 调查达到的深度幅度 (R $\sim$ 26) 对于评估潜在的 GRB 宿主很重要。采用瞬态分类方法来选择潜在的孤儿 GRB 余辉候选者。在对瞬态和宿主星系特性进行彻底分析后，我们得出结论，该调查领域没有候选者。零结果意味着考虑喷射结构对于进一步孤立的 GRB 余辉调查是必不可少的。