[论文解读] A Catalog of 157 X-ray Spectra and 84 Spectral Energy Distributions of Blazars observed with BeppoSAX

P. Giommi, M. Capalbi+6 more|ArXiv.org|Sep 27, 2002

Astrophysics and Cosmic Phenomena被引用 7

一句话总结

本文基于公开档案中的数据，对贝皮索斯（BeppoSAX）在前五年观测的157个X射线谱和84个宽波段能谱分布（SED）进行了统一分析。研究发现，同步辐射峰值频率跨越六个数量级，且在高能峰值BL Lac源中，光谱曲率最适宜用对数抛物线模型描述，表明粒子加速过程在更高能量下效率降低。

ABSTRACT

As a special contribution to the proceedings of the BeppoSAX workshop dedicated to blazar astrophysics we present a catalog of 157 X-ray spectra and the broad-band Spectral Energy Distribution (SED) of 84 blazars observed by BeppoSAX during its first five years of operations. The SEDs have been built by combining BeppoSAX LECS, MECS and PDS data with (mostly) non-simultaneous multi-frequency photometric data, obtained from NED and from other large databases, including the GSC2 and the 2MASS surveys. All BeppoSAX data have been taken from the public archive and have been analysed in a uniform way. For each source we present a SED plot, and for every BeppoSAX observation we give the best fit parameters of the spectral model that best describes the data. The energy where the maximum of the synchrotron power is emitted spans at least six orders of magnitudes ranging from ~ 0.1 eV to over 100 keV. A wide variety of X-ray spectral slopes have been seen depending on whether the synchrotron or inverse Compton component, or both, are present in the X-ray band. The wide energy bandpass of BeppoSAX allowed us to detect, and measure with good accuracy, continuous spectral curvature in many objects whose synchrotron radiation extends to the X-ray band. This convex curvature, which is described by a logarithmic parabola law better than other models, may be the spectral signature of a particle acceleration process that becomes less and less efficient as the particles energy increases. Finally some brief considerations about other statistical properties of the sample are presented.

研究动机与目标

• 编制一份全面且经过统一分析的贝皮索斯观测耀变体的X射线谱和宽波段SED星表。
• 研究耀变体在X射线波段的光谱多样性，特别是其同步辐射成分的形状与曲率。
• 确定在X射线选源中观测到的光谱曲率是否比简单模型（如折返幂律）更适用于对数抛物线模型。
• 探讨光谱曲率对耀变体喷流中粒子加速机制的物理意义。
• 评估样本中的选择效应，特别是贝皮索斯观测策略导致的对X射线明亮、高峰值频率源的偏向。

提出的方法

• 从公开档案中获取所有贝皮索斯LECS、MECS和PDS数据，并以一致、统一的方式重新分析。
• 通过结合贝皮索斯X射线数据与来自NED、GSC2和2MASS的非同时多波段测光数据，构建SED。
• 使用对数抛物线模型进行光谱拟合以描述曲率，参数β和E0用于量化光谱形状。
• 通过将同步辐射自反Compton（SSC）模型拟合至SED，估算同步辐射峰值频率ν_peak。
• 对FSRQs和BL Lacs分别进行ν_peak分布的统计分析，以评估选择偏差。
• 将光谱指数与通量比f_x/f_r与ν_peak相关联，以检验早期ROSAT研究的预测。

实验结果

研究问题

• RQ1 在贝皮索斯样本中，耀变体观测到的同步辐射峰值频率ν_peak的范围是什么？
• RQ2 对同步辐射延伸至X射线波段的耀变体，对数抛物线模型在多大程度上能更好地描述其X射线光谱曲率？
• RQ3 观测到的光谱曲率对耀变体喷流中粒子加速机制具有何种物理意义？
• RQ4 观测到的SED分布在多大程度上受到贝皮索斯观测策略的影响，该策略偏向于X射线明亮、高ν_peak源？
• RQ5 是否存在超高端能量峰值BL Lac源（UHBLs）的候选体，其同步辐射峰值达到伽马射线波段？

主要发现

• 同步辐射峰值频率ν_peak至少跨越六个数量级，从约0.1 eV到超过100 keV，覆盖了LBL、HBL，甚至可能包括UHBL的范围。
• 对数抛物线模型对HBL源的光谱曲率拟合效果优于折返幂律模型，平均β参数为−0.38 ± 0.1。
• 观测到的光谱曲率与粒子加速过程在更高能量下效率降低的假设一致，因为β值比低能峰值BL Lac源更陡。
• 在多个源中检测到从软X射线区到硬X射线区的光谱由陡变平的显著过渡，表明这是同步辐射与反Compton辐射之间的过渡。
• 样本在BL Lac子样本中表现出对X射线明亮HBL源的强烈偏向，而FSRQs则主要为低ν_peak源，这与它们更高的总体光度以及X射线峰值FSRQ的稀有性一致。
• 仅发现一个FSRQ（1ES 1627+402）的同步辐射峰值位于X射线波段，证实其在FSRQ群体中极为罕见。