Electron and Proton Heating in Transrelativistic Magnetic Reconnection
Electron and Proton Heating in Transrelativistic Magnetic Reconnection
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DOI：
10.3847/1538-4357/aa9380
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发表时间：
2017-08
期刊：
影响因子：
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通讯作者：
M. Rowan;L. Sironi;R. Narayan
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文献类型：
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作者：
M. Rowan;L. Sironi;R. Narayan
热的无碰撞吸积流，如银河系中心的Sgr A* 中的吸积流，为磁重联的研究提供了独特的环境。这里质子是非相对论性的，而电子可以是超相对论性的。通过二维粒子模拟，我们研究了跨相对论重联流出中的电子和质子加热（即，σ w <$0.1 - 1，其中磁化强度σ w是磁能密度与焓密度之比）。对于电子和质子，我们发现在高β i（这里β i是质子热压力与磁压力的比值）下的加热主要是绝热压缩（“绝热加热”），而在低β i下，它伴随着熵的真正增加（“不可逆加热”）。对于我们的基准点σ w = 0.1，β i ≥ 1处的不可逆热效率几乎与电子-质子温度比Te/Ti（我们从0.1变化到1）无关，并且在低β i极限下，它渐近于流入磁能的~ 2%。在低和中等的β i下，质子比电子更有效地被加热（系数为1/7），而如果Te/Ti = 1，电子和质子的加热效率在β i = 2时变得相当，此时两种物质开始时已经相对论热。我们发现，在相对论重联极限（σ w <$1）下，两种物质的加热效率也相当。我们的研究结果具有重要的意义的两个温度性质的碰撞吸积流，并可能提供次网格物理所需的广义相对论MHD模拟。
Hot collisionless accretion flows, such as the one in Sgr A* at our Galactic center, provide a unique setting for the investigation of magnetic reconnection. Here protons are nonrelativistic, while electrons can be ultrarelativistic. By means of 2D particle-in-cell simulations, we investigate electron and proton heating in the outflows of transrelativistic reconnection (i.e., σ w ∼ 0.1 – 1 , where the magnetization σ w is the ratio of magnetic energy density to enthalpy density). For both electrons and protons, we find that heating at high β i (here β i is the ratio of proton thermal pressure to magnetic pressure) is dominated by adiabatic compression (“adiabatic heating”), while at low β i it is accompanied by a genuine increase in entropy (“irreversible heating”). For our fiducial σ w = 0.1 , the irreversible heating efficiency at β i ≲ 1 is nearly independent of the electron-to-proton temperature ratio T e / T i (which we vary from 0.1 up to 1), and it asymptotes to ∼ 2 % of the inflowing magnetic energy in the low- β i limit. Protons are heated more efficiently than electrons at low and moderate β i (by a factor of ∼7), whereas the electron and proton heating efficiencies become comparable at β i ∼ 2 if T e / T i = 1 , when both species start already relativistically hot. We find comparable heating efficiencies between the two species also in the limit of relativistic reconnection ( σ w ≳ 1 ). Our results have important implications for the two-temperature nature of collisionless accretion flows and may provide the subgrid physics needed in general relativistic MHD simulations.