arXiv 0807.31332008-07-20astro-ph

3C 279宽线区对10 Gev ~ 1 Tev γ射线的吸收

Absorption of 10 Gev--1 Tev Gamma Rays by Radiation from Broad-Line Region in 3C 279

H. T. Liu, J. M. Bai, L. Ma

备注：: 29 pages, 7 figures, Received: 4 June 2008, Accepted in ApJ: 18 Jul 2008
发表信息：: 2008, ApJ, 688, 148.
DOI：: 10.1086/592039

摘要：

本文研究了3C 279产生的10 GeV-1 TeV γ射线在宽线区（BLR）漫辐射下的光子-光子对产生光学深度。假设极高能（VHE）γ射线光子强度的$E_γ^{-a_2}$谱为幂律谱，由MAGIC和HESS测量的积分光子通量推断出$a_1 \gtrsim 405$和$a_2\gtrsim 6.4$。基于此幂律谱，通过校正BLR（内部吸收）和河外背景光（外部吸收）的漫射光子上的光子-光子吸收来推断预吸收谱。γ射线发射区$R_{\rmγ}$的位置决定了这两个漫射辐射对10 GeV-1 TeV γ射线总吸收的相对贡献。内吸收使γ射线的谱形比只考虑外吸收的修正更为复杂，并可导致任意软化和硬化γ射线谱的形成。在研究10 GeV-1 TeV强耀变体的γ射线时，考虑内吸收是必要的。由于内部吸收而湮灭的伽马射线光子的能量可能主要在GeV附近再辐射。我们的结果表明，$R_{\rmγ}$可能是3C 279的BLR的内半径和外半径之间。这意味着对于强大的耀变体来说，$R_{\rmγ}$可能既不在BLR空腔内，也不在BLR外部，而是在BLR壳层内。在不久的将来，对$\it GLAST$、MAGIC、HESS和VERITAS的观测可以对伽马射线发射区相对于BLR的位置提供更多的限制。

英文摘要：

In this paper, we study the photon-photon pair production optical depth for 10 GeV--1 TeV gamma rays from 3C 279 due to the diffuse radiation of broad-line region (BLR). Assuming a power-law spectrum of $E_γ^{-a_2}$ for the photon intensity of very high energy (VHE) gamma rays, $a_1 \gtrsim 405$ and $a_2\gtrsim 6.4$ are inferred by the integrated photon fluxes measured by MAGIC and HESS. Based on this power-law spectrum, the pre-absorbed spectra are inferred by correcting the photon-photon absorption on the diffuse photons of the BLR (internal absorption) and the extragalactic background light (external absorption). Position of gamma-ray emitting region $R_{\rmγ}$ determines the relative contributions of this two diffuse radiation to the total absorption for 10 GeV--1 TeV gamma rays. The internal absorption could make spectral shape of gamma rays more complex than only corrected for the external absorption, and could lead to the formation of arbitrary softening and hardening gamma-ray spectra. It should be necessary for the internal absorption to be considered in studying 10 GeV--1 TeV gamma rays from powerful blazars. The energies of annihilated gamma-ray photons due to the internal absorption are likely to be mainly reradiated around GeV. Our results indicate that $R_{\rmγ}$ may be between the inner and outer radii of the BLR for 3C 279. This implies for powerful blazars that $R_{\rmγ}$ might be neither inside the BLR cavity nor outside the BLR, but be within the BLR shell. Observations of $\it GLAST$, MAGIC, HESS, and VERITAS in the near future could give more constraints on the position of the gamma-ray emitting region relative to the BLR.

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