Suzaku studies of the central engine in the typical type I Seyfert NGC 3227: detection of multiple primary X-ray continua with distinct properties

Journal Article · Fri Oct 10 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/794/1/2· OSTI ID:22370525

Noda, Hirofumi ^[1]; Makishima, Kazuo; Nakazawa, Kazuhiro; Sakurai, Soki; Miyake, Katsuma ^[2]; Yamada, Shin'ya ^[3]

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1. Nishina Center, Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198 (Japan)
2. Department of Physics, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
3. Department of Physics, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo, 192-0397 Japan (Japan)

The type I Seyfert galaxy NGC 3227 was observed by Suzaku six times in 2008, with intervals of ∼1 week and net exposures of ∼50 ks each. Among the six observations, the source varied by nearly an order of magnitude; it was brightest in the first observation with a 2-10 keV luminosity of 1.2 × 10{sup 42} erg s{sup –1}, while faintest in the fourth observation with 2.9 × 10{sup 41} erg s{sup –1}. As it became fainter, the continuum in the 2-45 keV band became harder, while the narrow Fe-Kα emission line, detected on all occasions at 6.4 keV of the source rest frame, remained approximately constant in the photon flux. Through a method of variability-assisted broadband spectroscopy, the 2-45 keV spectrum of NGC 3227 was decomposed into three distinct components. One is a relatively soft power-law continuum with a photon index of ∼2.3, weakly absorbed and highly variable on timescales of ∼5 ks; it was observed only when the source was above a threshold luminosity of ∼6.6 × 10{sup 41} erg s{sup –1} (in 2-10 keV), and was responsible for further source brightening beyond. Another is a harder and more absorbed continuum with a photon index of ∼1.6, which persisted through the six observations and varied slowly on timescales of a few weeks by a factor of ∼2. This component, carrying a major fraction of the broadband emission when the source is below the threshold luminosity, is considered as an additional primary emission. The last one is a reflection component with the narrow iron line, produced at large distances from the central black hole.

• OSTI ID: 22370525
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 794; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
APPROXIMATIONS
BLACK HOLES
DETECTION
DISTANCE
EMISSION
IRON
KEV RANGE
LUMINOSITY
PHOTONS
REFLECTION
SEYFERT GALAXIES
SPECTRA
SPECTROSCOPY
X RADIATION
X-RAY GALAXIES