| 摘要 | BL Lac天体是一类性质极为特殊的活动星系核，非热连续谱、大幅快速光变、高偏振、无发射线或弱发射线是其主要观测特征。本文主要对BL Lac天体的红外谱指数，红外辐射性质，红外辐射和γ射线辐射的相关性等方面进行研究。 我们利用交叉认证的方法得到了833个BL Lac天体的2MASS观测数据(J,H, Ks星等)，这些源构成了迄今为止最大的近红外选BL Lac天体样本。其中的260个BL Lac天体包括在First Fermi/LAT AGN Catalog(1LAC)中，被称为Fermi-detected BL Lacs(FBLs); 剩余的573个BL Lac天体没有包括1LAC中，被称为non-FBLs。基于这个大样本，我们研究了BL Lac天体的近红外波段辐射性质，主要结论如下: (1) FBLs的2MASS探测率比non-FBLs的要高很多( 95%vs 49%); (2) 平均来说FBLs比non-FBLs更亮、光度更高; (3) 低频BL Lac天体(LBLs)的近红外谱比高频BL Lac天体(HBLs)的更亮、更陡，中频BL Lac天体(IBLs)的近红外谱介于这两者的之间; (4) 近红外谱指数、Ks波段光度都与同步辐射峰值频率存在着显著的负相关; (5) 在J-H-H-Ks双色图中，绝大部分(66%)的BL Lac天体沿幂律线分布或靠得很近，表明这些BL Lac天体的近红外辐射以非热辐射为主，同时我们还挑选出了更靠近黑体线的218个BL Lac天体，它们的近红外辐射很可能被寄主星系的热辐射所污染; (6) 近红外波段和γ射线波段的谱指数和流量都存在显著的正相关。 最近的多项研究成果表明: 相对于non-FBLs而言，FBLs具有更极端的物理性质，例如更快的喷流运动、更加致密的射电核、更高的射电偏振、更高的亮温度等。利用交叉认证的方法，我们得到了158个FBL的WISE观测数据(W1, W2, W3, W4波段星等)。这些FBL 包括在Second Fermi/LAT AGN Catalog(2LAC)中，我们研究了它们的中红外辐射特性，主要结论如下: (I)在W1-W2-W2-W3双色图中，几乎所有FBL落入WISE Blazar strip(WBS, Massaro et al. 2011)中，表明这些FBL的中红外辐射以非热辐射为主; (II) 绝大部分FBL的中红外谱指数比近红外谱指数要小，表明用单一幂律谱来描述中红外-近红外宽谱并不很合适; (III) 中红外谱指数、W3波段光度都与同步辐射峰值频率存在显著的负相关，表明从LBLs到IBLs再到HBLs，中红外谱逐渐变暗变平; (IV) 中红外波段和γ射线波段的谱指数和流量都存在着显著的正相关，γ射线噪度(γ-ray-MIR loudness, Gr)与同步辐射峰值频率之间存在着显著的正相关，这两个相关性支持BL Lac天体的γ射线来自于同步自康普顿辐射机制。 |
| 其他摘要 | BL Lac objects (BL Lacs) are a special subclass of active galaxy nuclei, characterized by non-thermal continuum emission, large amplitude and rapid flux variability, high polarization degree and absent (or weak) emission lines. In this thesis, we mainly study the IR spectral indices, the IR emission properties and the correlation between IR and γ-ray emission in BL Lacs. Making use of cross-identification method, we get 2MASS observational data (J, H, Ks magnitudes) of 833 BL Lacs. These BL Lacs constitute the largest IR-selected BL Lac sample. 260 BL Lacs therein are included by the First Fermi/LAT AGN Catalog (1LAC), called Fermi-detected BL Lacs (ab. FBLs); the remaining 573 BL Lacs are not in the 1LAC, called non-FBLs. Based on this large sample, we study the NIR emission properties of BL Lacs and get the fol- lowing results: (1) The 2MASS detection rate of FBLs is much larger than that of non-FBLs (∼95% vs 49%); (2) FBLs are on average brighter and more luminous than non-FBLs in the NIR bands; (3) The NIR spectra of low-frequency-peaked BL Lacs (LBLs) are on average brighter and more luminous than those of high-frequency-peaked BL Lacs, and the NIR spectra of intermediate-frequency- peaked BL Lacs (IBLs) seem to bridge those of LBLs and those of HBLs; (4) Both the NIR spectral index and the Ks band luminosity are significantly anti- correlated with the frequency of synchrotron peak; (5) In the J-H-H-Ks color-color diagram, most (∼66%) of BL Lacs in our sample are located along or close to the Power Law Line (PLL), indicating that their NIR emission is dominantly non-thermal. Besides, we pick out 218 BL Lacs which are located closer to the Black Body Line (BBL) in the color-color diagram. The NIR emission of these BL Lacs are probably significantly contaminated by the thermal emission of host galaxies; (6) The spectral index and flux of γ-ray band are significantly correlated with those of NIR band, respectively. Several recent research work show that FBLs have more extreme properties than non-FBLs (e.g., faster jet motions, more compact radio cores, stronger polarization near the base of the jet, higher brightness temperature of jet cores). Making use of cross-identification method, we get WISE observational data (W1, W2, W3, W4 magnitudes) of 158 FBLs. These FBLs are listed in the Second Fermi/LAT AGN Catalog (2LAC). We study the MIR emission properties of these FBLs and get the following results: (I) In the W1-W2-W2-W3 color-color diagram, the great majority of FBLs fall in the WISE Blazar strip (WBS, Massaro et al. 2011), giving a evidence that their MIR emission is predominantly non-thermal; (II) For most FBLs the MIR spectral index is less than the NIR spectral index, implying that a single power law is not appropriate to describe the MIR-NIR broad-band spectrum; (III) Both the MIR spectral index and the W3 band luminosity are significantly anti-correlated with the frequency of synchrotron peak. From LBLs to IBLs then to HBLs, the MIR spectra become darker and flatter; (IV) The spectral index and flux of γ-ray band are significantly correlated with those of MIR band, respectively. The γ-ray-MIR loudness (Gr) is significantly correlated with the frequency of synchrotron peak. These significant correlations indicate that the γ-rays in BL Lacs are most likely from SSC process. |
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