发表机构
Indian Institute of Technology; Nicolaus Copernicus University; Indian Institute of Astrophysics（印度理工学院; 尼古拉·哥白尼大学; 印度天体物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过时间分辨光谱研究超长伽马射线暴GRB 220627A，发现其谱演化类似磁星但能量远超磁星上限，支持蓝超巨星坍缩星起源。
AI 中文摘要
超长伽马射线暴（ul-GRBs）对标准坍缩星模型提出了挑战，因为其极端持续时间要求中心引擎活跃约10^3-10^4秒。由于典型伽马射线暴持续时间短，其瞬时谱演化难以分辨，而ul-GRBs为在延长的时间尺度上研究谱演化提供了独特机会。我们对GRB 220627A进行了时间分辨光谱研究，这是已知最亮的ul-GRBs之一（各向同性等效能量E_iso~10^54尔格，T_90>1000秒），由两个明亮的发射片段组成，中间间隔约600秒的静止期。利用一种基于HOP算法的新型分割方法，我们确定了时间分辨光谱的最佳时间间隔。康普顿化幂律（CPL）模型很好地描述了所有时间尺度上的瞬时发射（约10 keV-40 MeV）。Fermi-GBM光谱揭示出从第一片段期间硬的、慢冷却同步辐射谱（α_I=-0.70）到第二片段期间较软的、快冷却同步辐射谱（α_II=-1.29）的转变。这种演化与磁星候选体GRB 091024A的演化非常相似，突显出仅基于光谱演化可能存在前身星简并性。然而，极端的各向同性等效能量超过了磁星自转减速可提供的最大能量，强烈支持蓝超巨星（BSG）坍缩星起源。延长的活动和多片段结构可通过经过扩展恒星包层的持续吸积自然解释。我们的结果表明，ul-GRBs可以表现出类似磁星的光谱演化，同时由BSG坍缩星提供能量。GRB 220627A突显了将时间分辨光谱与能量约束相结合以区分前身星情景并理解ul-GRBs物理起源的必要性。
英文摘要
Ultra-long gamma-ray bursts (ul-GRBs) challenge standard collapsar models because their extreme durations require central engines active for $\sim10^{3}-10^{4}$ s. While the prompt spectral evolution of typical GRBs is difficult to resolve due to their short durations, ul-GRBs provide a unique opportunity to study spectral evolution on extended timescales. We present a time-resolved spectroscopic study of GRB 220627A, one of the most luminous ul-GRBs known ($E_{\rm iso}\sim10^{54}$ erg, $T_{90}>1000$ s), consisting of two bright emission episodes separated by $\sim600$ s quiescent interval. Using a novel HOP algorithm-based segmentation method, we identify optimal time intervals for time-resolved spectroscopy. A Comptonized power-law (CPL) model well describes the prompt emission ($\sim 10$ keV-40 MeV) across all timescales. Fermi-GBM spectroscopy reveals a transition from a hard, slow-cooling synchrotron spectrum ($α_{\rm I}=-0.70$) during episode-I to a softer, fast-cooling synchrotron spectrum ($α_{\rm II}=-1.29$) during episode-II. This evolution closely resembles that of the magnetar-candidate GRB 091024A, highlighting a potential progenitor degeneracy based solely on spectral evolution. However, the extreme isotropic-equivalent energy exceeds the maximum energy available from magnetar spin-down, strongly favouring a blue supergiant (BSG) collapsar origin. The prolonged activity and multi-episode structure are naturally explained by sustained accretion through an extended stellar envelope. Our results demonstrate that ul-GRBs can display magnetar-like spectral evolution while being powered by BSG collapsars. GRB 220627A highlights the need for combining time-resolved spectroscopy with energetic constraints to distinguish between progenitor scenarios and understand the physical origin of ul-GRBs.
Comments18 pages, 6 figures
