The correlated optical and radio variability of BL Lacertae WEBT data analysis 1994-2005
The correlated optical and radio variability of BL Lacertae WEBT data analysis 1994-2005
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DOI：
10.1051/0004-6361/200912065
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发表时间：
2009-05
影响因子：
6.5
通讯作者：
M. Villata;C. Raiteri;V. Larionov;V. Larionov;V. Larionov;M. Nikolashvili;M. Aller;U. Bach;D. Ca
中科院分区：
文献类型：
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作者：
M. Villata;C. Raiteri;V. Larionov;V. Larionov;V. Larionov;M. Nikolashvili;M. Aller;U. Bach;D. Ca
背景：自1997年以来，BL Lacertae经历了一个高光学活动阶段，发生了几次突出的爆发。从1999年开始，全球Blazar望远镜（WEBT）联盟组织了各种多频活动，收集了数万个数据点。研究这个巨大数据集的主要问题之一是寻找光通量和射电通量变化之间的相关性，以及光变曲线中可能的周期性。对前四次战役期间收集的数据（包括1968-2003年期间的档案数据）进行分析，发现1994-2003年的光-无线电相关性良好，硬无线电事件延迟约100天。此外，各种统计方法表明存在一个约8年的射电周期。目的：2004年，WEBT开始了一项新的活动，将数据集扩展到最近的观测季节，以便可能确认和更好地理解以前的结果。研究方法：在这次活动中，我们从20个望远镜收集和收集了大约11000个新的光学观测数据，以及各种频率的近红外和无线电数据。在这里，我们进行相关分析的长期R波段和无线电光变曲线。结果如下：总的来说，我们确认硬射电事件相对于光学事件的延迟约为100天，即使在特定时期也发现了更长的时间滞后（约200-300天）。射电的准周期性也得到了证实，但在过去的三个周期中，“周期”似乎从7.4年逐渐延长到9.3年。过去四十年的光学和无线电行为表明，几何效应起着重要作用。特别是，交替的增强和抑制的光学活性（伴随着硬和软无线电事件，分别）可以解释在发射等离子体流动沿着旋转螺旋路径在一个弯曲的射流。本文中介绍的无线电到光学数据存储在WEBT档案中;有关其可用性的问题，请联系WEBT主席Massimo Villata。
Context: Since 1997, BL Lacertae has undergone a phase of high optical activity, with the occurrence of several prominent outbursts. Starting from 1999, the Whole Earth Blazar Telescope (WEBT) consortium has organized various multifrequency campaigns on this blazar, collecting tens of thousands of data points. One of the main issues in the study of this huge dataset has been the search for correlations between the optical and radio flux variations, and for possible periodicities in the light curves. The analysis of the data assembled during the first four campaigns (comprising also archival data to cover the period 1968-2003) revealed a fair optical-radio correlation in 1994-2003, with a delay of the hard radio events of ~100 days. Moreover, various statistical methods suggested the existence of a radio periodicity of ~8 years. Aims: In 2004 the WEBT started a new campaign to extend the dataset to the most recent observing seasons, in order to possibly confirm and better understand the previous results. Methods: In this campaign we have collected and assembled about 11 000 new optical observations from twenty telescopes, plus near-IR and radio data at various frequencies. Here, we perform a correlation analysis on the long-term R-band and radio light curves. Results: In general, we confirm the ~100-day delay of the hard radio events with respect to the optical ones, even if longer (~200-300 days) time lags are also found in particular periods. The radio quasi-periodicity is confirmed too, but the “period” seems to progressively lengthen from 7.4 to 9.3 years in the last three cycles. The optical and radio behaviour in the last forty years suggests a scenario where geometric effects play a major role. In particular, the alternation of enhanced and suppressed optical activity (accompanied by hard and soft radio events, respectively) can be explained in terms of an emitting plasma flowing along a rotating helical path in a curved jet. The radio-to-optical data presented in this paper are stored in the WEBT archive; for questions regarding their availability, please contact the WEBT President Massimo Villata.