Origin of the X-ray Spectral Variation
and Seemingly Broad Iron Line
Structure in the Seyfert Galaxies
Ken EBISAWA
Naoki ISO, Takehiro MIYAKAWA,
Hajime INOUE
(JAXA/ISAS)
1
Contents of the Talk
1.
2.
3.
4.
Properties of the Seyfert Galaxies
Variable Partial Covering Model
Explanation of the Observed Properties
Conclusion
2
1. Properties of the Seyfert Galaxies
a) Significant flux variation
b) “Seemingly” broad iron-line feature
c) Small variation in the iron energy band
3
1a. Significant flux-variation
Suzaku observations of NGC4051 and NGC3516
(0.2—12 keV, 1bin=512sec）
Significant and aperiodic variations in various time-scales
4
1b.“Seemingly” broad iron-line feature
• ASCA MCG-6-30-15
(Tanaka+ 1995)
• Looks like an iron K-line “broadened” by relativistic effects
• Interpretation depends on the choice of models
5
1c. Small variation in the iron energy band
〜104 sec
〜105 sec
(Matsumoto+ 2003)
• MCG-6-30-15 with ASCA
Energy dependence of Root Mean Square (RMS) variation
• The RMS spectrum drops significantly at the iron K energy
6
band (model independent result!)
Contents of the Talk
1.
2.
3.
4.
Properties of the Seyfert Galaxies
Variable Partial Covering Model
Explanation of the Observed Properties
Conclusion
7
2. Variable Partial Covering Model
• Several authors have proposed idea of partial
covering for MCG-6-30-15: e.g., Matsuoka+
(1990); McKernan and Yaqoob (1998); Miller,
Turner and Reeves (2008, 2009)
• We have found “double partial covering” with
two different warm absorbers can explain the
Suzaku MCG-6-30-15 spectra (Miyakawa,
Ebisawa and Inoue 2012)
8
Double partial covering
X-ray source
xspec notation: partcov(a) * exp(-NHs(x))
Partial covering by thick absorber
with NH~1024.2cm-2 and x~101.6
and the partial covering fraction a
× partcov(a) exp(-NHs(x))
Partial covering by thin and
more ionized absorber with
NH~1022.1cm-2 and x~101.9 and
the same partial covering
fraction a
9
2. Variable Partial Covering Model
• Observed spectral variation of MCG-6-30-15 is
mostly explained by only variation of the
partial covering fraction (Miyakawa, Ebisawa
and Inoue 2012, PASJ, 64, 140)
• Variable Partial Covering model can explain
spectral variations of other 20 Seyfert galaxies
observed with Suzaku (Iso, Ebisawa+ 2013 in
prep.).
10
• Miyakawa, Ebisawa and Inoue (2012)
11
2. Variable Partial Covering Model
• Double Partial covering by absorbing clouds with thick core and thin envelope.
• The continuum spectrum composed of the direct component, absorbed component,
and outer-disk reflection component
• Observed spectral variation is mostly explained by only change of the covering
fraction α
Direct component
Heavily absorbed
component
Outer disk
reflection
12
Variable Partial Covering Model
(Miyakawa, Ebisawa and Inoue 2012)
The X-ray luminosity of BH hardly variable
Geometrical “covering fraction” is significantly variable
X-ray
source
direct
component
Heavily
absorbed
component
Ionized
absorbers
13
Variable Partial Covering Model
(Miyakawa, Ebisawa and Inoue 2012)
The X-ray luminosity of BH hardly variable
Geometrical “covering fraction” is significantly variable
Covering fraction varies
14
Variable Partial Covering Model
(Miyakawa, Ebisawa and Inoue 2012)
The X-ray luminosity of BH hardly variable
Geometrical “covering fraction” is significantly variable
Covering fraction varies
15
Variable Partial Covering Model
(Miyakawa, Ebisawa and Inoue 2012)
The X-ray luminosity of BH hardly variable
Geometrical “covering fraction” is significantly variable
Covering fraction varies
16
Variable Partial Covering Model
(Miyakawa, Ebisawa and Inoue 2012)
The X-ray luminosity of BH hardly variable
Geometrical “covering fraction” is significantly variable
Covering fraction varies
17
Variable Partial Covering Model
(Miyakawa, Ebisawa and Inoue 2012)
The X-ray luminosity of BH hardly variable
Geometrical “covering fraction” is significantly variable
Covering fraction varies
18
Variable Partial Covering Model
(Miyakawa, Ebisawa and Inoue 2012)
The X-ray luminosity of BH hardly variable
Geometrical “covering fraction” is significantly variable
Covering fraction: Null
19
Contents of the Talk
1.
2.
3.
4.
Properties of the Seyfert Galaxies
Variable Partial Covering Model
Explanation of the Observed Properties
Conclusion
20
解析
3. Explanation of the
Observed Properties
a. Significant flux variation
Flux variation of 21 Seyfert galaxies observed with
Suaku, explained by only change of the covering fraction
Counting rate
Covering fraction
21
Observed flux variations explained by “constant black hole
luminosity and variable covering fraction”.
22
Example of
other sources
Black:countig rate
Red:covering fraction
23
Example of
other sources
Black:countig rate
Red:covering fraction
24
Example of
other sources
Black:countig rate
Red:covering fraction
25
3. Explanation of the Observed Properties
b. “Seemingly” broad iron-line feature
The ionized iron-edge looks like a
broad iron line feature
direct
component
Heavily absorbed
component
outer-reflection
component
narrow
ion line
Suzaku MCG-6-30-15
Miyakawa, Ebisawa
and Inoue (2012)
26
3. Explanation of the Observed Properties
c. Small variation in the iron energy band
• In the Variable Partial Covering model, variations of the direct
component and absorbed component cancel each other
• This is most effective at the iron energy band
27
3. Explanation of the Observed Properties
c. Small variation in the iron energy band
• In the Variable Partial Covering model, variations of the direct
component and absorbed component cancel each other
• This is most effective at the iron energy band
direct compoent
absorbed
component
reflection
Iron line
28
解析
3. Explanation of the Observed Properties
c. Small variation in the iron energy band
• Observed Root Mean Square spectrum is explained by only
variation of the covering fraction
Black:data
Red:model
29
Example of
other sources
Black:data
Red:model
30
Example of
other sources
Black:data
Red:model
31
Example of
other sources
Black:data
Red:model
32
Contents of the Talk
1.
2.
3.
4.
Properties of the Seyfert Galaxies
Variable Partial Covering Model
Explanation of the Observed Properties
Conclusion
33
4. Conclusion
• We propose “Variable Partial Covering model” for
Seyfert Galaxies, where X-ray luminosity of the black
hole is hardly variable, and the observed spectral
variation is primarily due to variation of the warm
absorbers in the line of sight.
• In the Variable Partial Covering model, covering
fraction is the primary parameter to describe the
spectral variations.
• The Variable Partial Covering model successfully
explains observed spectral variations of 21 Seyfert
galaxies (including MCG-6-30-15) observed with
Suzaku.
34