2007年秋季3C 454.3的高活性。在AGILE检测期间由WEBT进行监测
The high activity of 3C 454.3 in autumn 2007. Monitoring by the WEBT during the AGILE detection
摘要：
类星体型耀变体3C 454.3在2007年夏季和秋季经历了一个高活动阶段，由全球耀变体望远镜（WEBT）在无线电到光学波段进行了密集监测。伽马射线卫星AGILE在2007年7月下旬和11月至12月首次探测到这个源。在这封信中，我们介绍了在第二个AGILE观测期间由WEBT和合作者收集的多频数据，并补充了来自Swift卫星上UVOT的一些同期数据。其目的是详细跟踪的行为的同步辐射从blazar喷流，并调查的贡献，从热发射组件。光学数据从大约20个望远镜已被均匀校准和仔细组装，以构建一个R波段光变曲线包含约1340个数据点，在42天。这种非常好的采样光学光变曲线使我们能够详细跟踪光源的显著通量变化。此外，我们显示了无线电到紫外光谱能量分布（SED）在不同的时期，这代表了不同的亮度水平。在所考虑的时期内，R波段的源在几周内变化了2.6等。观测到了许多快速（即夜间）变化的事件，最明显的是在12月12日，当时在1.5小时内检测到约1.1等的通量增加，然后在1小时内急剧下降约1.2等。由于银河系的不确定性，以及可能的内在因素，紫外波段的消光，热成分的贡献很难评估。然而，多项式拟合的无线电到紫外线的SED揭示了一个越来越多的光谱弯曲走向微弱的状态，这表明紫外线过量可能是由于从吸积盘的热发射。
英文摘要：
The quasar-type blazar 3C 454.3 underwent a phase of high activity in summer and autumn 2007, which was intensively monitored in the radio-to-optical bands by the Whole Earth Blazar Telescope (WEBT). The gamma-ray satellite AGILE detected this source first in late July, and then in November-December 2007. In this letter we present the multifrequency data collected by the WEBT and collaborators during the second AGILE observing period, complemented by a few contemporaneous data from UVOT onboard the Swift satellite. The aim is to trace in detail the behaviour of the synchrotron emission from the blazar jet, and to investigate the contribution from the thermal emission component. Optical data from about twenty telescopes have been homogeneously calibrated and carefully assembled to construct an R-band light curve containing about 1340 data points in 42 days. This extremely well-sampled optical light curve allows us to follow the dramatic flux variability of the source in detail. In addition, we show radio-to-UV spectral energy distributions (SEDs) at different epochs, which represent different brightness levels. In the considered period, the source varied by 2.6 mag in a couple of weeks in the R band. Many episodes of fast (i.e. intranight) variability were observed, most notably on December 12, when a flux increase of about 1.1 mag in 1.5 hours was detected, followed by a steep decrease of about 1.2 mag in 1 hour. The contribution by the thermal component is difficult to assess, due to the uncertainties in the Galactic, and possibly also intrinsic, extinction in the UV band. However, polynomial fitting of radio-to-UV SEDs reveals an increasing spectral bending going towards fainter states, suggesting a UV excess likely due to the thermal emission from the accretion disc.
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