Variability timescales of TeV blazars observed in the ASCA continuous long-look X-ray monitoring

被引:72
作者
Tanihata, C
Urry, CM
Takahashi, T
Kataoka, J
Wagner, SJ
Madejski, GM
Tashiro, M
Kouda, M
机构
[1] Inst Space & Astronaut Sci, Sagamihara, Kanagawa 2298510, Japan
[2] Univ Tokyo, Dept Phys, Bunkyo Ku, Tokyo 1130033, Japan
[3] Yale Univ, New Haven, CT 06520 USA
[4] Tokyo Inst Technol, Dept Phys, Tokyo 1528551, Japan
[5] Landessternwarte Heidelberg, D-69117 Heidelberg, Germany
[6] Stanford Linear Accelerator Ctr, Stanford, CA 94309 USA
[7] Saitama Univ, Dept Phys, Urawa, Saitama 3388570, Japan
关键词
BL Lacertae objects : individual (Markarian 421; Markarian; 501; PKS 2155-304); galaxies : active; radiation mechanisms : nonthermal; X-rays : galaxies;
D O I
10.1086/323960
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Three uninterrupted, long (lasting respectively 7, 10, and 10 days) ASCA observations of the well-studied TeV-bright blazars Mrk 421, Mrk 501, and PKS 2155-304 all show continuous strong X-ray flaring. Despite the relatively faint intensity states in two of the three sources, there was no identifiable quiescent period in any of the observations. Structure function analysis shows that all blazars have a characteristic timescale of similar to1 day, comparable to the recurrence time and to the timescale of the stronger flares. On the other hand, examination of these flares in more detail reveals that each of the strong flares is not a smooth increase and decrease but exhibits substructures of shorter flares having timescales of similar to 10 ks. We verify via simulations that in order to explain the observed structure function, these shorter flares ("shots") are unlikely to be fully random, but in some way are correlated with each other. The energy dependent cross-correlation analysis shows that interband lags are not universal in TeV blazars. This is important since in the past only positive detections of lags were reported. In this work, we determine that the sign of a lag may differ from flare to flare; significant lags of both signs were detected from several flares, while no significant lag was detected from others. However, we also argue that the nature of the underlying component can affect these values. The facts that all flares are nearly symmetric and that fast variability shorter than the characteristic timescale is strongly suppressed, support the scenario where the light crossing time dominates the variability timescales of the day-scale flares.
引用
收藏
页码:569 / 581
页数:13
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