Search for Type IL Gamma-ray Bursts: Criterion, Results, Verification and Physical Implication

Wen-Jun Tan; Chen-Wei Wang; Peng Zhang; Wang-Chen Xue; Shao-Lin Xiong; Bo-bing Wu; Jia-Cong Liu; Yue Wang; Sheng-Lun Xie; Zheng-Hang Yu; Jin-Peng Zhang; Wen-Long Zhang; Yan-Qiu Zhang; Chao Zheng

arXiv · 2504.06616

Search for Type IL Gamma-ray Bursts: Criterion, Results, Verification and Physical Implication

Wen-Jun Tan·Chen-Wei Wang·Peng Zhang·Wang-Chen Xue·Shao-Lin Xiong·Bo-bing Wu·Jia-Cong Liu·Yue Wang·Sheng-Lun Xie·Zheng-Hang Yu·Jin-Peng Zhang·Wen-Long Zhang·Yan-Qiu Zhang·Chao Zheng

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Abstract

As an interesting subclass of gamma-ray burst (GRB), Type IL GRB (such as GRB 211211A and GRB 230307A) features a long-duration prompt emission but originating from compact binary merger. The "long duration" emisison of Type IL GRB are dominately composed of the main burst, rather than the extended emission,differentiating them from the traditional "long-short" GRB (e.g., GRB 060614). Previous study has reported several Type IL GRBs by visual inspection of their light curves. In this work, we established a detailed criterion to identify Type IL GRBs by light curve, and then systematically searched the archival Fermi/GBM data with this criterion, resulting in a sample of 5 type IL GRBs from January 1, 2014 to January 1, 2024, i.e. GRB 230307A, GRB 211211A, GRB 200914A, GRB 200311A and GRB 170228A. Apart from the light curve pattern, we find that the temporal and spectral properties of these 5 GRBs also support this classification. Interestingly, we find that the energy ratio between extended emission and main emission is almost constant (~0.7, with small scattering) for these GRBs, which have strong implication on the mechanism of Type IL burst. We discuss theoretical models to interpret the progenitor, central engine, and extended emission of these Type IL bursts.

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Wen-Jun Tan, Chen-Wei Wang, Peng Zhang, Wang-Chen Xue, Shao-Lin Xiong, Bo-bing Wu, Jia-Cong Liu, Yue Wang, Sheng-Lun Xie, Zheng-Hang Yu, Jin-Peng Zhang, Wen-Long Zhang, Yan-Qiu Zhang, Chao Zheng. 2025-04-09. Search for Type IL Gamma-ray Bursts: Criterion, Results, Verification and Physical Implication. https://arxiv.org/abs/2504.06616

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