Using the database of the University of Michigan Radio Astronomy Observatory （UMRAO） at three radio frequencies （4.8, 8 and 14.5 GHz）, we determined the short-term variability timescales for 166 radio sources. The timescales are 0.15d （2007＋777） to 176.17 d （0528-250） with an average timescale of Atobs = 17.1 4- 16.5 d for the whole sample. The timescales are used to calculate the brightness temperatures, TB. The value of log TB is in the range of log TB = 10.47 to 19.06 K. In addition, we also estimated the boosting factor for the sources. The correlation between the polarization and the Doppler factor is also discussed.
射电星系根据其在178MHz处的光度可以分为两类,即Fanaroff-Riley type Is(FRIs)和Fanaroff-Riley type IIs(FRIIs),而且FRIs的光度要低于FRIIs(Fanaroff&Riley1974).从SIMBAD网站上找到了许多个光学星等多于两个波段的源.在星等转化为流量密度时考虑了银河系修正,然后对于这些流量密度进行线性拟合,得到各个源的光学谱指数.对于这些谱指数,取它们的取值范围在-2到3之间,且α≥2Δα,最终得到153个源可用(61FRIs和92FRIIs).对FRIs和FRIIs的光学谱指数分布进行高斯拟合,发现FRIs的平均光学谱指数等于1.60±0.66,大于FRIIs的值1.13±1.09.然后我们对这两类源进行K-S检验,发现这两类源来自同一母体的概率是4.73E-6,这可以说明这两类源在光学波段可以被区分开.
Gamma-ray bursts(GRBs) are divided into two classes according to their durations.We investigate if the softness of bursts plays a role in the conventional classification of the objects.We employ the BATSE(Burst and Transient Source Experiment) catalog and analyze the duration distributions of different groups of GRBs associated with distinct softness.Our analysis reveals that the conventional classification of GRBs with the duration of bursts is influenced by the softness of the objects.There exists a bimodality in the duration distribution of GRBs for each group of bursts and the time position of the dip in the bimodality histogram shifts with the softness parameter.Our findings suggest that the conventional classification scheme should be modified by separating the two well-known populations in different softness groups,which would be more reasonable than doing so with a single sample.According to the relation between the dip position and the softness parameter,we get an empirical function that can roughly set apart the short-hard and long-soft bursts:SP =(0.100 ± 0.028) T-(0.85 0.18) 90,± where SP is the softness parameter adopted in this paper.
费米伽玛射线空间大区域望远镜(Large Area Telescope,LAT),以前称为Gamma ray Large Area Space Telescope(GLAST))比Energetic Gamma Ray Experiment Telescope(EGRET)提高了观测精度,在服役的初始几个月中已经检测到一些具有快速光变伽玛射线源.用LAT观测结果并结合EGRET观测到的伽玛噪Blazar天体的变化时标和伽玛射线光度来估计天体的中心黑洞质量.我们发现中心黑洞质量下限范围为(0.3～24)×107M⊙,并将此结果与其他作者的研究结果进行了比较,发现结果是一致的.我们也给出了18个有已知超光速伽玛噪Blazar天体的洛伦兹因子(Γ)和视角(θ).
