GRB 240529A: A Tale of Two Shocks

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Abstract
Thanks to the rapidly increasing time-domain facilities, we are entering a golden era of research on gamma-ray bursts (GRBs). In this Letter, we report our observations of GRB 240529A with the Burst Optical Observer and Transient Exploring System, the 1.5 m telescope at Observatorio de Sierra Nevada, the 2.5 m Wide Field Survey Telescope of China, the Large Binocular Telescope, and the Telescopio Nazionale Galileo. The prompt emission of GRB 240529A shows two comparable energetic episodes separated by a quiescence time of roughly 400 s. Combining all available data on the GRB Coordinates Network, we reveal the simultaneous apparent X-ray plateau and optical rebrightening around 103–104 s after the burst. Rather than the energy injection from the magnetar as widely invoked for similar GRBs, the multiwavelength emissions could be better explained as two shocks launched from the central engine separately. The optical peak time and our numerical modeling suggest that the initial bulk Lorentz factor of the later shock is roughly 50, which indicates that the later jet should be accretion driven and have a higher mass loading than a typical one. The quiescence time between the two prompt emission episodes may be caused by the transition between different accretion states of a central magnetar or black hole, or the fallback accretion process. A sample of similar bursts with multiple emission episodes in the prompt phase and sufficient follow-up could help to probe the underlying physics of GRB central engines.
Funding Information
  • MOST ∣ National Natural Science Foundation of China (12273113)
  • MOST ∣ National Natural Science Foundation of China (12321003)
  • MOST ∣ National Natural Science Foundation of China (12393812)
  • MOST ∣ National Natural Science Foundation of China (12393813)
  • MOST ∣ National Natural Science Foundation of China (12025303)
  • National SKA Program of China (2020SKA0120302)
  • National SKA Program of China (2022SKA0130100)
  • Strategic Priority Research Program of the Chinese Academy of Sciences (XDB0550400)
  • International Partnership Program of Chinese Academy of Sciences for Grand Challenges (114332KYSB20210018)
  • Youth Innovation Promotion Association (2023331)
  • Spanish Ministry projects (PID2020-118491GB-I00)
  • Spanish Ministry projects (PID2023-151905OB-I00)
  • Junta de Andalucía Grant (P20_010168)
  • SEVERO OCHOA GRANT (CEX2021-001131-S)
  • Academy of Finland project (325806)
  • ANID programs (11241477)
  • Millennium Science Initiative Programs (NCN2023_002)
  • Millennium Science Initiative Programs (ICN12_009)
  • Science Foundation Ireland grant (19/FFP/6777)
  • GRAWITA Large Program Grant (1.05.12.01.04)
  • Korean National Research Foundation (NRF-2017K1A4A3015188)
  • Korean National Research Foundation (NRF-2021R1A2B5B03002645)
  • PRIN-MIUR 2017 (20179ZF5KS)

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