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arXiv 1202.6529astro-ph.HEhep-ph
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来自PKS 1222+216的类轴子粒子的证据?

Evidence for an axion-like particle from PKS 1222+216?

F. Tavecchio, M. Roncadelli, G. Galanti, G. Bonnoli

摘要:

MAGIC令人惊讶地发现,平谱射电类星体PKS 1222+216在70 - 400 GeV的能量范围内强烈、快速变化的发射对所有解释方案都是一个挑战。事实上,为了避免在宽线区(BLR)密集的紫外辐射场中吸收γ射线,人们不得不援引一些非常规的天体物理学图像,例如,在距离喷流底部很远(R \sim 10 ^{18} cm)处存在一个非常紧凑(r \sim 10 ^{14} cm)的发射团。我们基于PKS 1222+216的标准blazar模型对一种情况进行了研究,在这种情况下,γ射线产生于靠近中央发动机的地方,但我们增加了新的假设,即在源内部光子可以振荡成类轴子粒子(ALP),这是基本粒子相互作用标准模型的几个扩展的一般预测。因此,相当一部分的极高能量光子可以通过光子ALP振荡的机制逃脱BLR的吸收,就像它们在nG范围内的大尺度磁场存在下在宇宙距离上传播时在很大程度上避免了河外背景光的吸收一样。此外,我们表明,上述MAGIC观测和同时费米/LAT观测的能量范围为0.3 - 3 GeV的模型参数的实验允许的值都可以用一个标准的光谱能量分布来解释。特别是,我们需要一个非常轻的ALP,就像宇宙空间中的光子ALP振荡一样。此外,我们发现这是相当诱人的,最有利的值的光子ALP耦合恰好是相同的,在这两种情况下。虽然我们的ALP不能对冷暗物质做出贡献,但它们是典型的暗能量的可行候选者。[删节]

英文摘要:

The surprising discovery by MAGIC of an intense, rapidly varying emission in the energy range 70 - 400 GeV from the flat spectrum radio quasar PKS 1222+216 represents a challenge for all interpretative scenarios. Indeed, in order to avoid absorption of γrays in the dense ultraviolet radiation field of the broad line region (BLR), one is forced to invoke some unconventional astrophysical picture, like for instance the existence of a very compact (r\sim 10^{14} cm) emitting blob at a large distance (R \sim10^{18} cm) from the jet base. We offer the investigation of a scenario based on the standard blazar model for PKS 1222+216 where γrays are produced close to the central engine, but we add the new assumption that inside the source photons can oscillate into axion-like particles (ALPs), which are a generic prediction of several extensions of the Standard Model of elementary particle interactions. As a result, a considerable fraction of very-high-energy photons can escape absorption from the BLR through the mechanism of photon-ALP oscillations much in the same way as they largely avoid absorption from extragalactic background light when propagating over cosmic distances in the presence of large-scale magnetic fields in the nG range. In addition we show that the above MAGIC observations and the simultaneous Fermi/LAT observations in the energy range 0.3 - 3 GeV can both be explained by a standard spectral energy distribution for experimentally allowed values of the model parameters. In particular, we need a very light ALP just like in the case of photon-ALP oscillations in cosmic space. Moreover, we find it quite tantalizing that the most favorable value of the photon-ALP coupling happens to be the same in both situations. Although our ALPs cannot contribute to the cold dark matter, they are a viable candidate for the quintessential dark energy. [abridged]

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