Synchrotron self absorption and the minimum energy of optically thick radio flares from stellar mass black holes
Synchrotron self absorption and the minimum energy of optically thick radio flares from stellar mass black holes
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同步加速器自吸收和恒星质量黑洞光学厚射电耀斑的最小能量
DOI：
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发表时间：
2019
影响因子：
4.8
通讯作者：
J. Bright
中科院分区：
文献类型：
--
作者：
R. Fender;J. Bright
我们考虑的情况下，从黑洞X射线双星的耀斑光谱演变从光学厚光学薄，假设这是由于减少光学深度同步自吸收的射电耀斑。我们能够把上限和下限的大小与无线电耀斑的发射区域，并确定同步辐射源的磁场和能量作为大小的函数。能量有一个明确的最小值发生在接近的条件，即来自同步自吸收的磁场等于从均分计算。这种最小能量估计与事件的上升时间无关，因此可以应用于任何测量峰值通量并有自吸收证据的事件。这是一种比假设以接近光速的速度膨胀更准确的最小能量估计方法。我们应用这种方法的光学厚射电耀斑的四个例子，发现在每种情况下，无论是同步加速器源的填充因子是远远小于单位，或膨胀速度是远远小于光速。对于我们考虑的四个事件中的三个事件，单位填充因子和接近光速的膨胀速度的组合在能量上完全被排除。推断的放缓扩张与最近在文献中报道的此类事件的详细建模一致。与耀斑相关的最小功率要求被发现是1036 erg s−1，这很容易在恒星质量黑洞吸积的背景下在近爱丁顿水平，当这些耀斑通常发生。然而，真正的喷气动力仍然可能高出几个数量级。
We consider the case of radio flares from black hole X-ray binaries in which the flare spectrum evolves from optically thick to optically thin, under the assumption that this is due to decreasing optical depth to synchrotron self absorption. We are able to place upper and lower limits on the size of the emitting region associated with a radio flare, and determine the synchrotron source magnetic field and energy as a function of size. The energy has a clear minimum which occurs close to the condition that the magnetic field derived from synchrotron self absorption equals that calculated from equipartition. This minimum energy estimate is independent of the rise time of the event, and so may be applied to any event for which the peak flux is measured and there is evidence for self-absorption. This is a much more accurate approach to minimum energy estimation than assuming expansion at close to the speed of light. We apply this method to four examples of optically thick radio flares and find that in each case either the filling factor of the synchrotron source is considerably less than unity, or the expansion speed is considerably less than the speed of light. The combination of unity filling factor and expansion speeds close to the speed of light is completely ruled out on energetic grounds for three of the four events we consider. The inferred slowed expansion is consistent with detailed modelling of such events which has been recently reported in the literature. The minimum power requirements associated with the flares are found to be ∼1036 erg s−1, which are easily accomodated in the context of stellar mass black hole accretion at near-Eddington levels, when these flares typically occur. However, the true jet power could still be orders of magnitude higher.