Anisotropic Energy Injection from Magnetar Central Engines in Short GRBs
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| Format: | Preprint |
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2023
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| _version_ | 1866911753211740160 |
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| author | Wang, Yihan Zhang, Bing Zhu, Zhaohuan |
| author_facet | Wang, Yihan Zhang, Bing Zhu, Zhaohuan |
| contents | A long-lived magnetar, potentially originating from a binary neutron star system, has been proposed to explain the extended emission observed in certain short-duration gamma-ray bursts (sGRBs), and is posited as a potential central engine to power the engine-fed kilonovae. Previously, the process by which energy is injected into the surrounding ejecta/jet was widely believed to be nearly isotropic. In this study, we employ special relativity magnetohydrodynamic (SRMHD) simulations to investigate the wind injection process from a magnetar central engine. We explore the dynamics and energy distribution within the system and found that the parameter $α=u_{\rm A}/u_{\rm MWN}$ can be used to indicate the collimation of the magnetar wind energy injection, where $u_{\rm A}$ is the local Alfven four-speed and $u_{\rm MWN}$ is the four-speed of the magnetar wind nebular (MWN) formed from wind-ejecta collision. A significant portion of the injected energy from the magnetar spin-down wind will be channeled to the jet axis due to collimation within the MWN. Achieving isotropic energy injection requires a significantly small $α$ that necessitates either an ultra-relativistic expanding MWN or an extremely low magnetization MWN, both of which are challenging to attain in sGRBs. Consequently, a considerably reduced energy budget (i.e. energy per solid angle reduced by a factor of up to 10 with respect to the value under isotropic assumption) is anticipated to be injected into the ejecta for engine-fed kilonovae. Engine-fed kilonovae would appear fainter than originally anticipated. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2309_15141 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Anisotropic Energy Injection from Magnetar Central Engines in Short GRBs Wang, Yihan Zhang, Bing Zhu, Zhaohuan High Energy Astrophysical Phenomena A long-lived magnetar, potentially originating from a binary neutron star system, has been proposed to explain the extended emission observed in certain short-duration gamma-ray bursts (sGRBs), and is posited as a potential central engine to power the engine-fed kilonovae. Previously, the process by which energy is injected into the surrounding ejecta/jet was widely believed to be nearly isotropic. In this study, we employ special relativity magnetohydrodynamic (SRMHD) simulations to investigate the wind injection process from a magnetar central engine. We explore the dynamics and energy distribution within the system and found that the parameter $α=u_{\rm A}/u_{\rm MWN}$ can be used to indicate the collimation of the magnetar wind energy injection, where $u_{\rm A}$ is the local Alfven four-speed and $u_{\rm MWN}$ is the four-speed of the magnetar wind nebular (MWN) formed from wind-ejecta collision. A significant portion of the injected energy from the magnetar spin-down wind will be channeled to the jet axis due to collimation within the MWN. Achieving isotropic energy injection requires a significantly small $α$ that necessitates either an ultra-relativistic expanding MWN or an extremely low magnetization MWN, both of which are challenging to attain in sGRBs. Consequently, a considerably reduced energy budget (i.e. energy per solid angle reduced by a factor of up to 10 with respect to the value under isotropic assumption) is anticipated to be injected into the ejecta for engine-fed kilonovae. Engine-fed kilonovae would appear fainter than originally anticipated. |
| title | Anisotropic Energy Injection from Magnetar Central Engines in Short GRBs |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2309.15141 |