TY - JOUR
T1 - JHK′ imaging photometry of Seyfert 1 active galactic nuclei and quasars. II. Observation of long-term variability
AU - Enya, Keigo
AU - Yoshii, Yuzuru
AU - Kobayashi, Yukiyasu
AU - Minezaki, Takeo
AU - Suganuma, Masahiro
AU - Tomita, Hiroyuki
AU - Peterson, Bruce A.
PY - 2002/7
Y1 - 2002/7
N2 - Observations of 226 AGNs in the near-infrared J, H, and K′ bands are presented along with the analysis of the observations for variability. Our sample consists mainly of Seyfert 1 AGNs and QSOs. About a quarter of the objects in each category are radio loud. The AGNs in the entire sample have the redshifts spanning the range from z = 0 to 1, and the absolute magnitudes from MB = -29 to -18. All the objects were observed twice, and their variability was measured by differential photometry. A reduction method of differential photometry, optimized to the analysis of extended images, has been developed. The systematic error in variability arising from AGNs of highly extended images is estimated to be less than 0.01 mag in each of the J, H, and K′ bands. The systematic error arising from the flat-fielding is negligible for most AGNs, although it is more than 0.1 mag for some particular cases. The overall average flat-fielding error is 0.03 mag for the image pairs. We find that these systematic errors are superseded by statistical errors, and the overall average total systematic and statistical errors amounts to 0.05 mag in the measured variability in each band. We find that 58% of all the AGNs in the entire sample show variability of more than 2 σ, and 44% of more than 3 σ. This result holds independent of the J, H, and K′ bands. The detection rate of variability is higher for a subsample of higher photometric accuracy, and there appears no limit to this tendency. In particular, when we consider a subsample with small photometric errors of σ < 0.03 mag, the rate of 2 σ detection is 80%, and 64% for 3 σ detection. This suggests that most AGNs are variable in the near-infrared.
AB - Observations of 226 AGNs in the near-infrared J, H, and K′ bands are presented along with the analysis of the observations for variability. Our sample consists mainly of Seyfert 1 AGNs and QSOs. About a quarter of the objects in each category are radio loud. The AGNs in the entire sample have the redshifts spanning the range from z = 0 to 1, and the absolute magnitudes from MB = -29 to -18. All the objects were observed twice, and their variability was measured by differential photometry. A reduction method of differential photometry, optimized to the analysis of extended images, has been developed. The systematic error in variability arising from AGNs of highly extended images is estimated to be less than 0.01 mag in each of the J, H, and K′ bands. The systematic error arising from the flat-fielding is negligible for most AGNs, although it is more than 0.1 mag for some particular cases. The overall average flat-fielding error is 0.03 mag for the image pairs. We find that these systematic errors are superseded by statistical errors, and the overall average total systematic and statistical errors amounts to 0.05 mag in the measured variability in each band. We find that 58% of all the AGNs in the entire sample show variability of more than 2 σ, and 44% of more than 3 σ. This result holds independent of the J, H, and K′ bands. The detection rate of variability is higher for a subsample of higher photometric accuracy, and there appears no limit to this tendency. In particular, when we consider a subsample with small photometric errors of σ < 0.03 mag, the rate of 2 σ detection is 80%, and 64% for 3 σ detection. This suggests that most AGNs are variable in the near-infrared.
KW - Galaxies: Seyfert
KW - Galaxies: active
KW - Galaxies: photometry
KW - Infrared: galaxies
KW - Quasars: general
UR - http://www.scopus.com/inward/record.url?scp=0036305128&partnerID=8YFLogxK
U2 - 10.1086/339507
DO - 10.1086/339507
M3 - Article
SN - 0067-0049
VL - 141
SP - 31
EP - 44
JO - Astrophysical Journal, Supplement Series
JF - Astrophysical Journal, Supplement Series
IS - 1
ER -