Spectral evolution of non-thermal electron distributions in intense radiation fields
Spectral evolution of non-thermal electron distributions in intense radiation fields
复制标题
强辐射场中非热电子分布的光谱演化
DOI：
10.1051/0004-6361:20078298
复制
发表时间：
2007
影响因子：
6.5
通讯作者：
Heidelberg
中科院分区：
文献类型：
--
作者：
K. Manolakou;D. Horns;J. W. I. F. Astronomy;A. Tuebingen;H Germany;M. Kernphysik;Heidelberg
上下文许多天体物理伽马射线源的模型假设它们包含均匀分布的电子，这些电子以能量的幂律注入，并通过与辐射场，磁场和源中的粒子相互作用和逃逸而演变。如果辐射场具有比磁场更高的能量密度，并且能量足够大，使得逆康普顿散射不限于汤姆逊区，则该问题特别复杂。目标。我们提出了一个简单的，依赖于时间的，半解析解的电子动力学方程，处理连续和脉冲注入，冷却通过同步加速器和逆康普顿辐射（考虑克莱因-西科效应），和energydependent粒子逃逸。我们用这个解决方案来计算的多波长光谱的系统中，高能电子在强光子场冷却的时间演化。方法.用拉普拉斯变换法求解任意含时源函数的动力学方程。使用的能量损失率的近似表达式，考虑到同步辐射和逆康普顿损失，包括克莱因-Nishina效应散射过的各向同性光子场的幂律或黑体分布，我们找到明确的表达式的冷却时间和逃逸概率的个别电子。这使得完整的时间相关的解决方案可以减少到一个单一的正交。从电子分布，我们然后构建时间相关的，多波长的发射光谱。结果我们将我们的解决方案与几种极限情况进行比较，并讨论光谱特征的一般外观和时间行为（即，冷却中断、碰撞等）。作为一个具体的例子，我们的宽带能谱的开放恒星协会Westerlund-2在其演化的不同时期的模型，并将其与观测结果进行比较。模型计算匹配的年龄大于1010 - 5 yrs的源的观测。我们预测，GLAST伽马射线天文台应该很容易检测到这个源。结论.我们提出的技术，使简单的，计算效率高，时间依赖性模型的均匀源被构造和多波长观测比较。
Context. Models of many astrophysical gamma-ray sources assume they contain a homogeneous distribution of electrons that are injected as a power law in energy and evolve by interacting with radiation fields, magnetic fields, and particles in the source and by escaping. This problem is particularly complicated if the radiation fields have higher energy density than the magnetic field and are sufficiently energetic that inverse Compton scattering is not limited to the Thomson regime. Aims. We present a simple, time-dependent, semi-analytical solution to the electron kinetic equation that treats both continuous and impulsive injection, cooling via synchrotron and inverse Compton radiation (taking Klein-Nishina effects into account), and energydependent particle escape. We used this solution to calculate the temporal evolution of the multi-wavelength spectrum of systems where energetic electrons cool in intense photon fields. Methods. The kinetic equation for an arbitrary, time-dependent source function is solved by the method of Laplace transformations. Using an approximate expression for the energy-loss rate that takes synchrotron and inverse Compton losses into account, including Klein-Nishina effects for scattering off an isotropic photon field with either a power-law or black-body distribution, we find explicit expressions for the cooling time and escape probability of individual electrons. This enables the full, time-dependent solution to be reduced to a single quadrature. From the electron distribution, we then construct the time-dependent, multi-wavelength emission spectrum. Results. We compare our solutions with several limiting cases and discuss the general appearance and temporal behaviour of spectral features (i.e., cooling breaks, bumps, etc.). As a specific example, we model the broad-band energy spectrum of the open stellar association Westerlund-2 at different times of its evolution, and compare it with observations. The model calculation matches the observations for a source with an age greater than ≈10 5 yrs. We predict that the GLAST gamma-ray observatory should easily detect this source. Conclusions. The technique we present enables simple, computationally efficient, time-dependent models of homogeneous sources to be constructed and compared with multi-wavelength observations.