Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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INTRA-NIGHT OPTICAL VARIABILITY OF ACTIVE GALACTIC NUCLEI IN THE COSMOS FIELD WITH THE KMTNET

  • Kim, Joonho (Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University) ;
  • Karouzos, Marios (Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University) ;
  • Im, Myungshin (Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University) ;
  • Choi, Changsu (Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University) ;
  • Kim, Dohyeong (Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University) ;
  • Jun, Hyunsung D. (School of Physics, Korea Institute for Advanced Study) ;
  • Lee, Joon Hyeop (Korea Astronomy and Space Science Institute) ;
  • Mezcua, Mar (Institute of Space Sciences (ICE, CSIC), Campus UAB)
  • Received : 2018.04.26
  • Accepted : 2018.07.11
  • Published : 2018.08.31
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Abstract

Active Galactic Nucleus (AGN) variability can be used to study the physics of the region in the vicinity of the central black hole. In this paper, we investigated intra-night optical variability of AGN in the COSMOS field in order to understand the AGN instability at the smallest scale. Observations were performed using the KMTNet on three separate nights for 2.5 to 5 hours at a cadence of 20 to 30 min. We find that the observation enables the detection of short-term variability as small as ~ 0.02 and 0.1 mag for R ~ 18 and 20 mag sources, respectively. Using four selection methods (X-rays, mid-infrared, radio, and matching with SDSS quasars), 394 AGN are detected in the $4deg^2$ field of view. After differential photometry and ${\chi}^2$-test, we classify intra-night variable AGN. The fraction of variable AGN (0-8%) is statistically consistent with a null result. Eight out of 394 AGN are found to be intra-night variable in two filters or two nights with a variability level of 0.1 mag, suggesting that they are strong candidates for intra-night variable AGN. Still they represent a small population (2%). There is no sub-category of AGN that shows a statistically significant intra-night variability.

Keywords

References

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