GRB 210610B: The Internal and External Plateau as Evidence for the Delayed Outflow of Magnetar

• Published in: Research in astronomy and astrophysics Vol. 24; no. 7; pp. 75013 - 75023
• Main Authors: Wei, Yi-Ning, Wang, Xiang-Gao, Lin, Da-Bin, Zheng, Wei-Kang, Chen, Liang-Jun, Yan, Sheng-Yu, Yi, Shuang-Xi, Wang, Qi, Zhou, Zi-Min, Liu, Hui-Ya, Liang, En-Wei
• Format: Journal Article
• Language: English
• Published: Beijing National Astromonical Observatories, CAS and IOP Publishing 01.07.2024; IOP Publishing
• Subjects: (stars:) gamma-ray burst: general; (stars:) gamma-ray burst: individual (GRB 210610B); Afterglows; Decay; Ejecta; Energy; Energy dissipation; Fluctuations; Gamma ray bursts; Gamma rays; Injection; Light curve; Lorentz factor; Luminosity; Magnetars; Magnetic dipoles; Markov chains; Monte Carlo simulation; Outflow; stars: jets; X-ray fluxes; X-rays
• ISSN: 1674-4527; 2397-6209
• DOI: 10.1088/1674-4527/ad4d3a

Abstract After launching a jet, outflows of magnetar were used to account for the achromatic plateau of afterglow and the early X-ray flux plateau known as “internal plateau”. The lack of detecting magnetic dipole emission together with the energy injection feature in a single observation poses confusion until the long gamma-ray burst (GRB) 210610B is detected. GRB 210610B is presented with an optical bump following an early X-ray plateau during the afterglow phase. The plateau followed by a steep decline flux overlays in the steadily decaying X-ray flux with index α X,1 ∼ 2.06, indicating an internal origin and that can be fitted by the spin-down luminosity law with the initial plateau luminosity log 10 L X ∼ 48.29 erg s − 1 and the characteristic spin-down timescale T ∼ 2818 s. A subsequent bump begins at ∼4000 s in the R band with a rising index α R,1 ∼ − 0.30 and peaks at ∼14125 s, after which a decay index α R,2 ∼ 0.87 and finally transiting to a steep decay with α R,3 ∼ 1.77 achieve the closure relation of the external shock for the normal decay phase as well as the magnetar spin-down energy injection phase, provided that the average value of the photon index Γ γ = 1.80 derived from the spectral energy distributions (SEDs) between the X-ray and optical afterglow. The closure relation also works for the late X-ray flux. Akin to the traditional picture of GRB, the outflow powers the early X-ray plateau by dissipating energy internally and collides with the leading decelerating blast burst as time goes on, which could interpret the exotic feature of GRB 210610B. We carry out a Markov Chain Monte Carlo simulation and obtain a set of best parameters: ϵ B ≃ 4.7 × 10 −5 , ϵ e ≃ 0.15, E K,iso ≃ 4.6 × 10 53 erg, Γ 0 ≃ 832, A * ≃ 0.10, L inj,0 ≃ 3.55 × 10 50 erg s −1 . The artificial light curve can fit the afterglow data well. After that, we estimated the average Lorentz factor and the X-ray radiation efficiency of the later ejecta are 35% and 0.13%, respectively.