Study of the Ultra-Long GRB 220627A: Exploring a Possible Blue Supergiant Collapsar Origin

@misc{garg2026study,
  title = {{Study of the Ultra-Long GRB 220627A: Exploring a Possible Blue Supergiant Collapsar Origin}},
  author = {Ayush Garg and Amit Shukla and Dorottya Szécsi and G. C. Anupama},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.02889},
  eprint = {2610.02889},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.02889},
}

TY  - UNPB
TI  - Study of the Ultra-Long GRB 220627A: Exploring a Possible Blue Supergiant Collapsar Origin
AU  - Ayush Garg
AU  - Amit Shukla
AU  - Dorottya Szécsi
AU  - G. C. Anupama
PY  - 2026
DA  - 2026/10/02
PB  - arXiv
DO  - 10.48550/arxiv.2610.02889
UR  - https://arxiv.org/abs/2610.02889
AB  - Ultra-long gamma-ray bursts (ul-GRBs) challenge standard collapsar models because their extreme durations require central engines active for ∼10^3−10^4 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_iso∼10^54 erg, T_90>1000 s), consisting of two bright emission episodes separated by ∼600 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 (∼ 10 keV-40 MeV) across all timescales. Fermi-GBM spectroscopy reveals a transition from a hard, slow-cooling synchrotron spectrum (α_I=−0.70) during episode-I to a softer, fast-cooling synchrotron spectrum (α_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.
ER  -