The Double-burst Nature and Early Afterglow Evolution of Long GRB 110801A

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Abstract
We present a comprehensive temporal and spectral analysis of the long-duration gamma-ray burst GRB 110801A, utilizing multiband data from the Neil Gehrels Swift Observatory and ground-based telescopes. The gamma-ray emission exhibits a distinct two-episode (“double-burst”) structure. Rapid follow-up observations in the optical and X-ray bands provide full coverage of the second burst. The optical light curve begins to rise approximately 135 s after the trigger, significantly preceding the second emission episode observed in X-rays and gamma rays at ∼320 s. This chromatic behavior suggests different physical origins for the optical and high-energy emissions. Joint broadband spectral fitting (optical to gamma rays) during the second episode reveals that a two-component model, consisting of a power law plus a Band function, provides a superior fit compared to single-component models. We interpret the power-law component as the afterglow of the first burst (dominating the optical band), while the Band component is attributed to the prompt emission of the second burst (dominating the high-energy bands). A physical synchrotron model is also found to be a viable candidate to explain the high-energy emission. Regarding the afterglow, the early optical light curve displays a sharp transition from a rise of ∼ t 2.5 to ∼ t 6.5 , which is well-explained by a scenario involving both reverse shock and forward shock components. We constrain the key physical parameters of the burst, deriving an initial Lorentz factor Γ 0 ∼ 60, a jet half-opening angle θ j ∼ 0.09, and an isotropic kinetic energy E k,iso ∼ 10 54.8 erg.
Funding Information
  • National Key Research and Development Program of China (2024YFA1611704)
  • National Key Research and Development Program of China (2024YFA1611700)
  • National Natural Science Foundation of China (12225305)
  • National Natural Science Foundation of China (12473049)
  • National Natural Science Foundation of China (12321003)
  • National Natural Science Foundation of China (12233011)
  • Strategic Priority Research Program of the Chinese Academy of Science (XDB0550400)
  • Jiangsu Funding Program for Excellent Postdoctoral Talent (2024ZB110)
  • Basic Research Program of Jiangsu Province (BK20251707)
  • Postdoctoral Innovation Talents Support Program (BX20250159)
  • Postdoctoral Fellowship program (GZC20241916)
  • General Fund of the China Postdoctoral Science Foundation (2024M763531)

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