The exploration of the soft X-ray excess in FSRQ 4C+21.35 during the 2014 X-ray flare

Author:

Zhao Keqin1ORCID,Yin Hongxing1,Hu Shaoming1,Huang Shifeng23ORCID,Qiao Erlin45,Cheng Huaqing45ORCID,Chen Xu1,Xu Jingran1ORCID

Affiliation:

1. Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Institute of Space Sciences, Shandong University , Weihai, Shandong 264209, China

2. CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China , Hefei 230026, China

3. School of Astronomy and Space Sciences, University of Science and Technology of China , Hefei 230026, China

4. Key Laboratory of Space Astronomy and Technology, National Astronomical Observatory, Chinese Academy of Sciences , Beijing 100012, China

5. School of Astronomy and Space Sciences, University of Chinese Academy of Sciences , 19A Yuquan Road, Beijing 100049, China

Abstract

ABSTRACT We report the soft X-ray excess feature and an opposite tendency between the optical/UV and X-ray bands during the flare that occurred in 2014 in flat-spectrum radio quasar (FSRQ) 4C+21.35 with the observations by Swift-XRT and Swift-UVOT. These unusual phenomena are rarely reported in FSRQs. The flare was covered from the optical to the X-ray while no prominent activity in the γ-ray was observed, which could be an indication of weaker jet activity during the flare. We carry out the spectral energy distribution ranging from the optical to X-ray based on four models which are the warm corona model (Model-1), the relativistic reflection model (Model-2), the corona with the jet model (Model-3), and the relativistic reflection with the jet model (Model-4). We find some extreme variation of the parameters in Model-2 and Model-4 and they are unable to explain the correlations between the optical/UV and X-ray bands. Model-1 and Model-3 can obtain reasonable parameters and provide an explanation for the observed opposite tendency between the optical/UV and X-ray bands. However, considering the weak jet activity during the X-ray flare, Model-1 is much preferred for describing the soft X-ray excess, hard X-ray emission, as well as the opposite tendency between the optical/UV and X-rays. Based on Model-1, it is suggested that the flare in 2014 is probably due to the variation of the geometry of the corona, which is expected to be more strictly tested with further observations in the future.

Funder

National Natural Science Foundation of China

Natural Science Foundation of Shandong

NASA

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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