WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008 Unveiling different emission components
WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008 Unveiling different emission components
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DOI：
10.1051/0004-6361/200912953
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发表时间：
2009-09
影响因子：
6.5
通讯作者：
C. Raiteri;M. Villata;A. Capetti;M. Aller;U. Bach;P. Calcidese;M. Gurwell;V. Larionov;J. Ohlert;K. Nilsson;A. Strigachev;E. al.
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作者：
C. Raiteri;M. Villata;A. Capetti;M. Aller;U. Bach;P. Calcidese;M. Gurwell;V. Larionov;J. Ohlert;K. Nilsson;A. Strigachev;E. al.
2007年至2008年，我们利用全地球Blazar望远镜（WEBT）在BL Lacertae上进行了一项新的多波长运动，涉及xmm -牛顿卫星的三个点，以研究其发射特性。37架望远镜从光学到无线电波段监测了这个源。亮度相对较低。在光学波段中发现了一些非常快速的变化。x射线能谱用幂律很好地拟合，光子指数约为2，光电吸收超过银河系值。然而，当考虑到视线上分子云的存在时，数据最好用双幂律拟合，这意味着x射线光谱是凹的。利用xmm -牛顿同步观测数据建立的光谱能量分布（SEDs）表明，同步辐射的峰值位于近红外波段，除了轻微的软x射线过剩外，还显示出明显的紫外线过剩。与先前x射线卫星观测的SEDs相比较表明，x射线光谱变化很大。我们将紫外线过剩归因于吸积盘的热发射，而其他宽带光谱特征归因于两个同步加速器组件的存在，以及它们相关的SSC发射。我们用黑体定律拟合热发射，用螺旋射流模型拟合非热分量。拟合表明圆盘温度大于20000k，光度大于6 × 10^44 erg/s。
In 2007-2008 we carried out a new multiwavelength campaign of the Whole Earth Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the XMM-Newton satellite, to study its emission properties. The source was monitored in the optical-to-radio bands by 37 telescopes. The brightness level was relatively low. Some episodes of very fast variability were detected in the optical bands. The X-ray spectra are well fitted by a power law with photon index of about 2 and photoelectric absorption exceeding the Galactic value. However, when taking into account the presence of a molecular cloud on the line of sight, the data are best fitted by a double power law, implying a concave X-ray spectrum. The spectral energy distributions (SEDs) built with simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations suggest that the peak of the synchrotron emission lies in the near-IR band, and show a prominent UV excess, besides a slight soft-X-ray excess. A comparison with the SEDs corresponding to previous observations with X-ray satellites shows that the X-ray spectrum is extremely variable. We ascribe the UV excess to thermal emission from the accretion disc, and the other broad-band spectral features to the presence of two synchrotron components, with their related SSC emission. We fit the thermal emission with a black body law and the non-thermal components by means of a helical jet model. The fit indicates a disc temperature greater than 20000 K and a luminosity greater than 6 x 10^44 erg/s.