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Iron K Line Variability in the Low-Luminosity Active Galactic Nucleus NGC 4579
The Astrophysical Journal
|June 3, 2000
Summary
Variability in the iron K emission line of the low-luminosity active galactic nucleus NGC 4579 suggests cold matter, possibly an accretion disk, is close to the nucleus.
Area of Science:
- Astronomy
- Astrophysics
- X-ray Astronomy
Background:
- Low-luminosity active galactic nuclei (LLAGNs) are crucial for understanding galaxy evolution.
- Previous observations of NGC 4579 in 1995 showed an iron K emission line.
Purpose of the Study:
- To investigate the iron K emission line in the LLAGN NGC 4579 using new ASCA observations.
- To determine the origin and location of the iron K emission line based on variability.
Main Methods:
- Performed new ASCA X-ray observations of NGC 4579 in December 1998.
- Analyzed the spectral data, focusing on the iron K emission line energy and intensity.
- Compared new data with previous observations from 1995.
Main Results:
- Detected an iron K emission line at a lower energy (6.39 keV) in 1998 compared to 1995 (6.73 keV).
- Observed significant variability in the intensities of the 6.4 keV and 6.7 keV components of the iron line over 3.5 years.
- Ruled out host galaxy thermal plasmas as the source of the ionized iron line.
Conclusions:
- The variability indicates the presence of cold matter within approximately 1 parsec of the nucleus.
- The findings suggest an optically thick standard accretion disk is likely responsible for the iron line emission.
- The accretion disk is present at an Eddington ratio of approximately 2x10^-3, though its innermost structure remains unclear.