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Constraining broad-line regions from time lags of broad emission lines relative to radio emission

Authors

  • H. T. Liu,

    Corresponding author
    1. National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming, Yunnan 650011, China
    2. Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming, Yunnan 650011, China
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  • J. M. Bai,

    Corresponding author
    1. National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming, Yunnan 650011, China
    2. Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming, Yunnan 650011, China
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  • J. M. Wang,

    Corresponding author
    1. Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Beijing 100049, China
    2. Theoretical Physics Center for Science Facilities, Chinese Academy of Sciences, Beijing 100049, China
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  • S. K. Li

    Corresponding author
    1. National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming, Yunnan 650011, China
    2. Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming, Yunnan 650011, China
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E-mail: htliu@ynao.ac.cn (HTL); baijinming@ynao.ac.cn (JMB); wangjm@mail.ihep.ac.cn (JMW); lisk@ynao.ac.cn (SKL)

ABSTRACT

In this paper, a new method is proposed to estimate the broad-line region sizes of ultraviolet (UV) lines RuvBLR. It is applied to 3C 273. First, we derive the time lags of radio emission relative to broad emission lines Lyα and C iv by the z-transformed discrete correlation function (ZDCF) method. The broad lines lag the 5-, 8-, 15-, 22- and 37-GHz emission. The measured lags τuvob are of the order of years. For a given line, τuvob decreases as the radio frequency increases. This trend results from the radiative cooling of relativistic electrons. Both UV lines have a lag of τuvob=−2.74+0.06− 0.25 yr relative to the 37-GHz emission. These results are consistent with those derived from the Balmer lines in Paper I. Secondly, we derive the time lags of the lines Lyα, C iv, Hγ, Hβ and Hα relative to the 37-GHz emission by the flux randomization/random subset selection (FR/RSS) Monte Carlo method. The measured lags are τob=−3.40+0.31− 0.05, −3.40+0.41− 0.14, −2.06+0.36− 0.92, −3.40+1.15− 0.20 and −3.56+0.35− 0.18 yr for the lines Lyα, C iv, Hγ, Hβ and Hα, respectively. These estimated lags are consistent with those derived by the ZDCF method within the uncertainties. Based on the new method, we derive RuvBLR= 2.54+0.71− 0.35 to 4.01+0.90− 1.16 and 2.54+0.80− 0.43 to 4.01+0.98− 1.24 light-years for the Lyα and C iv lines, respectively. Considering the uncertainties, these estimated sizes are consistent with those obtained in the classical reverberation mapping for the UV and the Balmer lines. This indicates that their emitting regions are not separated so large as in the classical mapping of the UV and optical lines. These results seem to depart from the stratified ionization structures obtained in the classical mapping.

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