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arXiv 0807.1226astro-ph
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gamma-ray双星LS 5039和LSI +61 $\degr$ 303中自由脉冲星风的光谱特征

Spectral signature of a free pulsar wind in the gamma-ray binaries LS 5039 and LSI +61$\degr$303

Benoit Cerutti, Guillaume Dubus, Gilles Henri

摘要:

LS 5039和LSI +61 $\degr$ 303是已经在TeV能量域中检测到的两个二进制。这些双星由一颗大质量恒星和一颗致密天体组成,可能是一颗年轻的脉冲星。伽马射线的发射可能是由于相对论脉冲星风和大质量恒星的恒星风之间的碰撞部位的粒子加速。部分辐射也可能来自恒星光子在未受冲击(自由)脉冲星风上的逆康普顿散射。本工作的目的是通过计算无激波风辐射并与观测结果进行比较,来约束LS 5039和LSI +61 $\degr$ 303的紧凑脉冲星风星云情景中脉冲星风的体洛伦兹因子和激波几何。导出了各向异性反康普顿损失方程,并将其应用于双星中的自由脉冲星风。观测者所看到的未受冲击的风谱的计算考虑到伽玛-伽玛吸收和冲击几何。由单能对组成的脉冲星风产生一个典型的尖峰,其能量取决于体洛伦兹因子,其幅度取决于发射区的大小。在LS 5039和LSI +61 $\degr$ 303中发现,来自自由脉冲星风的这种辐射很强,很难避免。如果脉冲星中的粒子是单能的,那么观测将它们的能量限制在大约10-100 GeV。对于更复杂的粒子分布,自由脉冲星风辐射将很难与冲击脉冲星风辐射区分开来。

英文摘要:

LS 5039 and LSI +61$\degr$303 are two binaries that have been detected in the TeV energy domain. These binaries are composed of a massive star and a compact object, possibly a young pulsar. The gamma-ray emission would be due to particle acceleration at the collision site between the relativistic pulsar wind and the stellar wind of the massive star. Part of the emission may also originate from inverse Compton scattering of stellar photons on the unshocked (free) pulsar wind. The purpose of this work is to constrain the bulk Lorentz factor of the pulsar wind and the shock geometry in the compact pulsar wind nebula scenario for LS 5039 and LSI +61$\degr$303 by computing the unshocked wind emission and comparing it to observations. Anisotropic inverse Compton losses equations are derived and applied to the free pulsar wind in binaries. The unshocked wind spectra seen by the observer are calculated taking into account the gamma-gamma absorption and the shock geometry. A pulsar wind composed of monoenergetic pairs produces a typical sharp peak at an energy which depends on the bulk Lorentz factor and whose amplitude depends on the size of the emitting region. This emission from the free pulsar wind is found to be strong and difficult to avoid in LS 5039 and LSI +61$\degr$303. If the particles in the pulsar are monoenergetic then the observations constrain their energy to roughly 10-100 GeV. For more complex particle distributions, the free pulsar wind emission will be difficult to distinguish from the shocked pulsar wind emission.

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