NDLI: Infrared variability of the nucleus of the Seyfert galaxy NGC 1068 in 1998

Content Provider	Springer Nature Link
Author	Tarava, O. G. Shenavrin, V. I.
Copyright Year	2006
Abstract	Our 8-year-long JHKLM photometry of the Seyfert galaxy NGC 1068 has confirmed its IR variability. The amplitudes of the brightness variations in the J (1.25 µm) and K (2.2 µm) bands are within 0 . m 15 and 0 . m 3, respectively, and exceed the observational errors by more than a factor of 5. The nucleus of NGC 1068 is a variable source and can be at different phases of activity. The brightness of the galaxy in all bands except J decreased from 1998 until 2004. In this period, there was a tendency for the J brightness to increase. The variable source in NGC 1068 is a complex structured object. At least two sources radiate in the wavelength range 1.25–5 µm: a hot source whose radiation shows up in the range 1.25–1.65 µm and a cold source radiating at long wavelengths (2.2–5 µm). The color temperature of the hot source increased from 2300 K (the beginning of our observations) to ∼2700 K (the end of our observations). In contrast, the temperature of the cold source decreased by several tens of degrees (in the temperature range 800–900 K). The IR brightness and color variations observed in 1998–2004 are attributable to the dispersal of the dust envelope that formed around the galactic nucleus some 30 years ago and reached its maximum density in 1994–1995. Our analysis of the spectral energy distributions for the galaxy has shown that the observed radiation in the range 1.25–5 µm can be represented as the sum of radiations from two blackbody sources. For the first period of our observations (JD 2451400), the temperatures of the hot and cold sources are ∼3100 and 760 K, respectively. For the second period (JD 2453230), they are ∼3200 and 720 K, respectively. The hot source is relatively compact; it is smaller in size than the cold source by several tens of times. The mean sizes of the hot and cold sources are ∼2.35 × 10$^{16}$ and ∼7.8 × 10$^{17}$ cm, respectively. The total mean luminosity of the two sources did not change between the beginning and the end of our observations. The optical depth of the dust envelope averaged over the spectrum of the hot source is τ ∼ 1.5. In 2004, the state of the dust envelope almost returned to its 1974 level, i.e., the dust envelope formation and dispersal cycle was ∼11 000 days (∼30 yr).
Starting Page	439
Ending Page	445
Page Count	7
File Format	PDF
ISSN	10637737
Journal	Astronomy Letters
Volume Number	32
Issue Number	7
e-ISSN	15626873
Language	English
Publisher	Nauka/Interperiodica
Publisher Date	2006-01-01
Publisher Place	Moscow
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	galaxies groups and clusters of galaxies intergalactic gas Seyfert galaxies NGC 1068 IR variability Astronomy Astrophysics
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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