천문학회지 (Journal of The Korean Astronomical Society)

  • 제56권2호
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  • Pages.231-252
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  • 2023
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  • 1225-4614(pISSN)
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  • 2288-890X(eISSN)
한국천문학회 (The Korean Astronomical Society)
권호 표지
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Interferometric Monitoring of Gamma-Ray Bright AGNs: 4C +28.07 and Its Synchrotron Self-Absorption Spectrum

  • 투고 : 2023.09.16
  • 심사 : 2023.11.16
  • 발행 : 2023.12.30
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초록

We present the analysis results of the simultaneous multifrequency observations of the blazar 4C +28.07. The observations were conducted by the Interferometric Monitoring of Gamma-ray Bright Active Galactic Nuclei (iMOGABA) program, which is a key science program of the Korean Very Long Baseline Interferometry (VLBI) Network (KVN). Observations of the iMOGABA program for 4C +28.07 were conducted from 16 January 2013 (MJD 56308) to 13 March 2020 (MJD 58921). We also used γ-ray data from the Fermi Large Array Telescope (Fermi-LAT) Light Curve Repository, covering the energy range from 100 MeV to 100 GeV. We divided the iMOGABA data and the Fermi-LAT data into five periods from 0 to 4, according to the prosody of the 22 GHz data and the presence or absence of the data. In order to investigate the characteristics of each period, the light curves were plotted and compared. However, a peak that formed a hill was observed earlier than the period of a strong γ-ray flare at 43-86 GHz in period 3 (MJD 57400-58100). Therefore, we assumed that the minimum total CLEANed flux density for each frequency was quiescent flux (Sq) in which the core of 4C +28.07 emitted the minimum, with the variable flux (Svar) obtained by subtracting Sq from the values of the total CLEANed flux density. We then compared the variability of the spectral indices (α) between adjacent frequencies through a spectral analysis. Most notably, α22-43 showed optically thick spectra in the absence of a strong γ-ray flare, and when the flare appeared, α22-43 became optically thinner. In order to find out the characteristics of the magnetic field in the variable region, the magnetic field strength in the synchrotron self-absorption (BSSA) and the equipartition magnetic field strength (Beq) were obtained. We found that BSSA is largely consistent with Beq within the uncertainty, implying that the SSA region in the source is not significantly deviated from the equipartition condition in the γ-ray quiescent periods.

키워드

과제정보

We are grateful to the staff of the KVN, who helped us to operate the array and to correlate the data. The KVN is a facility operated by KASI (Korea Astronomy and Space Science Institute). The KVN observations and correlations are supported through high-speed network connections among the KVN sites provided by KREONET (Korea Research Environment Open NETwork), which is managed and operated by KISTI (Korea Institute of Science and Technology Information). This work has made use of Fermi-LAT data supplied by Abdollahi et al. (2023), https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository. This work was supported by a grant from the National Research Foundation of Korea (NRF) funded by the Korean government (MIST) (2020R1A2C2009003).

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