Title: The transition between BL Lac objects and Flat Spectrum Radio Quasars Show Chinese title

Title: BL Lac天体和光谱平坦射电类星体之间的转变

Abstract: We study the BL Lac objects detected in the one year all sky survey of the Fermi satellite, with a energy spectral slope alpha_gamma in the [0.1-100 GeV] band greater than 1.2. In the alpha_gamma vs gamma-ray luminosity plane, these BL Lacs occupy the region populated by Flat Spectrum Radio Quasars (FSRQs). Studying the properties of their spectral energy distributions (SED) and of their emitting lines, we find that several of these BL Lacs have a SED similar to FSRQs and that they do have broad lines of large equivalent width, and should be reclassified as FSRQs even adopting the current phenomenological definition (i.e. equivalent width EW of the emitting line greater than 5 A). In other cases, even if the EW width is small, the emitting lines can be as luminous as in quasars, and again their SED is similar to the SED of FSRQs. Sources classified as BL Lacs with a SED appearing as intermediate between BL Lacs and FSRQs also have relatively weak broad emission lines and small EW, and can be considered as transition sources. These properties are confirmed also by model fitting, that allows to derive the relevant intrinsic jet parameters and the jet power. This study leads us to propose a physical distinction between the two classes of blazars, based on the luminosity of the broad line region measured in Eddington units. The dividing line is of the order of L_BLR/L_Edd ~ 5e-4, in good agreement with the idea that the presence of strong emitting lines is related to a transition in the accretion regime, becoming radiatively inefficient below a disk luminosity of the order of one per cent of the Eddington one. Show Chinese abstract

Abstract: 我们研究了费米卫星一年全天巡天中检测到的BL Lac天体，在[0.1-100 GeV]波段的能量谱斜率alpha_gamma大于1.2。在alpha_gamma与伽马射线光度平面中，这些BL Lac天体占据了平坦谱射电类星体（FSRQs）所占据的区域。通过研究它们的能谱分布（SED）和发射线的特性，我们发现其中一些BL Lac天体的SED类似于FSRQs，并且它们确实具有大等效宽度的宽线，即使采用当前的现象学定义（即发射线的等效宽度EW大于5 A），也应重新归类为FSRQs。在其他情况下，即使EW宽度较小，发射线的亮度也可以与类星体相当，而且它们的SED同样类似于FSRQs的SED。被分类为BL Lac且SED介于BL Lac和FSRQ之间的天体也具有相对较弱的宽发射线和较小的EW，可以被视为过渡源。这些特性也通过模型拟合得到了确认，该拟合能够推导出相关的喷流内在参数和喷流功率。这项研究使我们提出基于宽线区光度（以爱丁顿单位测量）的两种耀变体类别的物理区分。分界线约为L_BLR/L_Edd ~ 5e-4，这与强发射线的存在与吸积模式转变相关的观点一致，在盘光度低于爱丁顿光度的百分之一以下时，吸积变得辐射低效。