The awakening of BL Lacertae: Observations by fermi, swift and the GASP-WEBT

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题名:	The awakening of BL Lacertae: Observations by fermi, swift and the GASP-WEBT
作者:	柯伊娜;Larionov, V.M;24420530 - Böttcher, Markus;Raiteri, C.M;Villata, M;Böttcher, M;D'Ammando, F
贡献者:	理學院天文研究所
关键词:	Astronomy;Correlation analysis;Sampling;Star & galaxy formation;X-ray astronomy
日期:	2013-12-01
上传时间:	2026-04-21 14:22:27 (UTC+8)
出版者:	Oxford University Press;London: Oxford University Press
摘要:	摘要： Since the launch of the Fermi satellite, BL Lacertae has been moderately active at γ-rays and optical frequencies until 2011 May, when the source started a series of strong flares. The exceptional optical sampling achieved by the GLAST–AGILE Support Program of the Whole Earth Blazar Telescope in collaboration with the Steward Observatory allows us to perform a detailed comparison with the daily γ-ray observations by Fermi. Discrete correlation analysis between the optical and γ-ray emission reveals correlation with a time lag of 0 ± 1 d, which suggests cospatiality of the corresponding jet emitting regions. A better definition of the time lag is hindered by the daily gaps in the sampling of the extremely fast flux variations. In general, optical flares present more structure and develop on longer time-scales than corresponding γ-ray flares. Observations at X-rays and at millimetre wavelengths reveal a common trend, which suggests that the region producing the mm and X-ray radiation is located downstream from the optical and γ-ray-emitting zone in the jet. The mean optical degree of polarization slightly decreases over the considered period and in general it is higher when the flux is lower. The optical electric vector polarization angle (EVPA) shows a preferred orientation of about 15°, nearly aligned with the radio core EVPA and mean jet direction. Oscillations around it increase during the 2011–2012 outburst. We investigate the effects of a geometrical interpretation of the long-term flux variability on the polarization. A helical magnetic field model predicts an evolution of the mean polarization that is in reasonable agreement with the observations. These can be fully explained by introducing slight variations in the compression factor in a transverse shock waves model. 其他題名： Mon. Not. R. Astron. Soc 出版者： London: Oxford University Press 出版日期： 2013-12-01 出處： Monthly Notices of the Royal Astronomical Society, 2013-12, Vol.436 (2), p.1530-1545 資源來源： Alma/SFX Local Collection 版權： 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society 2013 版權： Copyright Oxford University Press, UK Dec 1, 2013 識別號： ISSN: 0035-8711 識別號： ISSN: 1365-2966 識別號： ISSN: 1365-8711 識別號： EISSN: 1365-2966 識別號： DOI: 10.1093/mnras/stt1672
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