[论文解读] Photopolarimetric monitoring of 41 blazars in the optical and near-infrared bands with the Kanata telescope

Y. Ikejiri, Makoto Uemura+8 more|ArXiv.org|Dec 18, 2009

Astrophysics and Cosmic Phenomena参考文献 21被引用 7

一句话总结

本研究利用Kanata望远镜对41个耀星在光学与近红外波段进行了光度-偏振监测，发现83%的观测充分的耀星在爆发期间表现出‘越亮越蓝’的普遍颜色趋势，而三个天体仅在暗淡状态下表现出‘越亮越红’的行为，暗示热辐射占主导。偏振-流量相关性微弱，仅有10个天体显示出显著的正相关，且低光度耀星在流量、颜色和偏振度上的变化幅度较小。

ABSTRACT

Blazars are a kind of active galactic nuclei (AGN) in which a relativistic jet is considered to be directed along the line of sight. They are characterized by strong and rapid variability of the flux and high polarization. We performed a monitoring of 41 blazars in the optical and near-infrared regions from 2008 to 2009 using TRISPEC attached to the "Kanata" 1.5-m telescope. In this paper, we report the correlation of the flux, color and polarization using our data, and discuss universal features for blazars, which have not fully been established. Three blazars (3C 454.3, QSO 0454$-$234, and PKS 1510$-$089) tended to be redder when they were brighter, only during their faint states. This color behavior suggests that the contribution of a thermal component is strong in the faint states for those objects. Excluding this "redder-when-brighter" phase, we found that 24 blazars tended to be bluer when they were brighter. This number corresponds to 83% among well-observed objects which we observed for $>10$ nights. Thus, we conclude that the "bluer-when-brighter" trend is a universal feature for blazars. On the other hand, the correlation of the flux and the polarization degree is relatively weak; only 10 objects showed a significant positive correlation. We also investigated the luminosity-dependence of the color and polarization, and found that lower luminosity objects have smaller variation amplitudes both in the flux, color, and polarization degree.

研究动机与目标

• 研究耀星在光学与近红外波段中普遍的颜色与偏振变异性趋势。
• 确定‘越亮越蓝’趋势是否为不同耀星亚类的普遍特征。
• 在大样本耀星中，考察流量、偏振度与光度之间的关系。
• 评估暗淡状态下热辐射的作用及其对颜色演化的影响。

提出的方法

• 2008至2009年期间，利用Kanata 1.5米望远镜上的TRISPEC设备进行了光度-偏振监测。
• 对41个耀星在光学与近红外波段进行了多波段光度与偏振测量。
• 使用皮尔逊积矩相关系数分析颜色-星等关系与流量-偏振相关性。
• 根据光度与耀星类型（HBL、IBL、FSRQ）对天体进行分类，以研究光度依赖的变异性。
• 应用统计分析识别显著相关性，以超过10个观测夜晚为可靠结果的阈值。
• 对选定源使用双组分偏振模型，以分离与流量相关和独立的偏振成分。

实验结果

研究问题

• RQ1 ‘越亮越蓝’趋势是否为绝大多数耀星的普遍特征，还是仅限于特定亚类或状态？
• RQ2 耀星是否表现出‘越亮越红’趋势？若存在，其发生条件是什么？
• RQ3 流量与偏振度之间的相关性在样本中如何变化？这对辐射机制有何启示？
• RQ4 流量、颜色与偏振度的变化幅度是否依赖于耀星的本征光度？
• RQ5 观测到的偏振行为能否通过包含与流量相关和独立的偏振组分的双组分模型加以解释？

主要发现

• 在29个观测充分的耀星中，24个（83%）表现出‘越亮越蓝’趋势，表明该现象在爆发期间占主导地位，且可能为普遍特征。
• 三个耀星（3C 454.3、QSO 0454−234、PKS 1510−089）仅在暗淡状态下表现出‘越亮越红’趋势，提示吸积盘热辐射贡献增强。
• 即使在上述三个‘越亮越红’的天体中，‘越亮越蓝’趋势在明亮状态下依然重现，进一步支持其在活跃爆发期间的普遍性。
• 流量与偏振度之间的相关性微弱，仅有10个天体（34%）显示出显著正相关。
• 低光度耀星，尤其是HBL，其流量、颜色与偏振度的变化幅度小于高光度源。
• 低光度耀星的偏振度保持较低水平（0–5%），而高光度天体则观测到显著爆发，表明偏振行为具有光度依赖性。