Understanding X-ray Reflection in AGNDan WilkinsInstitute of AstronomyUniversity of Cambridge
IoA Wednesday Seminar, November 2011
1. Detailed X-ray observations of AGN
2. Emissivity profiles
• Determination from observations
• Spin considerations
3. Theoretical modelling
• What can we learn?
4. 1H 0707-495 – a change of ‘state’
Outline
2
10.5 2 510ï4
10ï3
2×10
ï45×
10ï4
2×10
ï35×
10ï3
keV
2 (Ph
oton
s cm
ï2 sï
1 keV
ï1)
Energy (keV)
1H 0707ï495
X-ray Spectra
3
• High quality X-ray spectra
• XMM-Newton EPIC pn
• Power law continuum
• Disc reflection
• Reverberation lags
• Further evidence for reflection
• Constrain distance of source from reflector
...and Timing
4
Zoghbi+09, Zoghbi+11
‘Lamppost’ Model
5
PLC
RDC
X-ray source in corona around BHIC scattering of seed photons
Reflection from accretion discatomic lines/absorption imprinted (reflionx)
Emissivity Profile
6
• Defined as the reflected power per unit area from disc
• Flux received at point on disc falls off with distance from X-ray source
1e-05
0.0001
0.001
0.01
0.1
1
10
0.1 1 10 100
¡
r
F / cos#
d2=
cos#
r2 + h2
#
r�3
Emissivity Profile
6
• Defined as the reflected power per unit area from disc
• Flux received at point on disc falls off with distance from X-ray source
d
h
• e.g. Euclidean space
r
Emissivity Profile - So What?
7
• Depends on
•Source location/height
•Source extent
•Source/disc geometry
•Typically assume a power law
•But can we learn something?
1 100.5 2 5
01
23
45
ratio
Energy (keV)
• Narrow emission line in disc frame
• To observer, broadened by relativistic effects:• Doppler shift/beaming• Gravitational redshift
• Effects are a function of emission radius
• See the integral over the disc
Broadened Emission Lines
8
105050
010
00no
rmali
zed
coun
ts s!1
keV!1
Energy (keV)
1.235 rg2 rg3 rg4 rg5 rg10 rg20 rg
Sum 1.235 rg < r < 100 rg
Broadened Emission Lines
9
• Line profiles different from successive radii
• Total line is sum (integral) over disc
• Photon count from each annulus
• Get emissivity from photon counts from each reflionx annulus (divided by projected area), found by minimising
Emissivity from Broad Lines
10
F0(⌫0) =X
T (re, g)redre✏(re)
N(r) / A(r)✏(r)
Wilkins & Fabian 2011
�2
! = 3.3
! = 6
" /
arbi
trar
y u
nits
10#10
10#9
10#8
10#7
10#6
10#5
10#4
10#3
0.01
r / RG
1 10 100
1H 0707-495 Emissivity Profile
11
3-10 keV
! = 3.3
! = 6
" /
arbi
trar
y u
nits
10#10
10#9
10#8
10#7
10#6
10#5
10#4
10#3
0.01
r / RG
1 10 100
1H 0707-495 Emissivity Profile
11
3-10 keV
?
! = 3.3
! = 6
" /
arbi
trar
y u
nits
10#10
10#9
10#8
10#7
10#6
10#5
10#4
10#3
0.01
r / RG
1 10 100
! = 0
! = 7.8
" /
arbi
trar
y u
nits
10#12
10#9
10#6
10#3
r / RG
1 10 100
1H 0707-495 Emissivity Profile
11
3-10 keV 3-5 keV
?
1 102 5
0.01
0.1
1Ph
oton
s cm!2
s!1 ke
V!1
Energy (keV)
a = 0.998a = 0.8a = 0.6a = 0.4a = 0.2a = 0
50.1
10.2
0.5Ph
otons
cm!2
s!1 ke
V!1
Energy (keV)
a = 0.998a = 0.8a = 0.6a = 0.4a = 0.2a = 0
• Spin changes ISCO – innermost emission/redshift
• Line profile from each radius not greatly affected though
• Can measure spin
Spin Considerations
12
1 2 3 4 5 6 7
0.2
0.4
0.6
0.8
1
Phot
ons
cm−2
s−1
keV
−1
Energy (keV)
Current Theoretical Model
drw 15−Aug−201
Spin Measurement from Lines
13
Emissivity, q = 3
1 2 3 4 5 6 7
0.2
0.4
0.6
0.8
1
Phot
ons
cm−2
s−1
keV
−1
Energy (keV)
Current Theoretical Model
drw 15−Aug−201
1 2 3 4 5 6 7
0.2
0.4
0.6
0.8
1
Phot
ons
cm−2
s−1
keV
−1
Energy (keV)
Current Theoretical Model
drw 15−Aug−201
Spin Measurement from Lines
13
Emissivity, q = 3 Emissivity, q = 7,3Rbr = 5rg
1
10
0.5
2
5
keV
2 (Ph
oton
s cm
ï2 sï
1 keV
ï1)
1 10 100
0.95
1
1.05
ratio
Energy (keV)
• Accreting black hole binary
• Suzaku(XIS, PIN, GSO)
Cygnus X-1
14
1 2 5
0.9
0.95
11.
051.
1
ratio
Energy (keV)
Cygnus X-1
! /
arbi
trar
y un
its
10"9
10"6
10"3
1
r/ rg
1 10 100
3-10 keV including diskpbb + gaussian (6.4keV)
Cygnus X-1 Emissivity Profile
15
• Highly ionised
• Blurred with strong edge
• Thermal disc continuum
• Narrow iron K line
• Systematic calculation of emissivity profiles to understand parameters
• Isotropic point source above the disc plane.
• Either on or orbiting the rotation axis.
• Trace rays from source until they hit disc plane.
• Emissivity – number of photons hitting disc per unit area.
16
Theoretical Emissivity ProfilesFollowing Miniutti+03, Suebsuwong+06
e0(t) = v
The X-ray Source
17
e0(a) · e0
(b) = ⌘(a)(b)
• Source frame basis (flat)
• Rays at equal intervals in solid angle
• Calculate initial conditions by transforming to global basis
• Isotropic Point Source• Equal power radiated into equal solid angle, in source frame
d⌦
0= d(cos ↵)d�!
"ei
e’i
#!
r
d$’
• Propagate photons using (null) geodesic equations as affine parameter advances.
Photon Propagation
18
• Accretion disc (equatorial plane) divided into radial bins.
• When photons hit disc (θ=π/2), record radial bin.
• Emissivity given by photons per bin (per bin area, with relativistic effects).
-4-2
0 2
4
-4
-2
0
2
4
0
1
2
3
4
5
Trace rays in parallel on GPU
A' /
dr
0.01
0.1
1
10
r / rg
1 10 100
Classical area, r drGR Disc Area! * GR Disc Arear dr / g! * GR Disc Area / g2
• Gravitational light bending towards black hole• Focusses more rays onto inner disc – steepens
emissivity profile.
• Relativistic beaming if source is moving• More emission onto regions of disc on/below orbit.
• Proper area of radial bins (GR and length contraction)
• A/dr increases in inner disc – shallower profile.
• Time dilation/gravitational redshift• Proper time elapses slower at inner disc so greater
flux measured in disc frame per ray – significant steepening.
Relativistic Effects
19
⇠ t2
Effective areas of annuli in disc
rs
! /
arbi
trar
y un
its
1
1000
106
r / rg
1 10 100
h = 1.235 rg
h = 3 rg
h = 5 rg
h = 10 rg
h = 15 rg
h = 20 rg
h = 25 rg
Theoretical Emissivity Profiles (1)
20
Stationary Axial Source
Theoretical Emissivity Profiles (2)
21
‘Co-rotating’ Ring Source(h = 5rg)
! /
arb
itrar
y un
its
1
10
100
104
105
106
107
r / rg
1 10 100
x = 1.235 rg
x = 3 rg
x = 5 rg
x = 10 rg
x = 15 rg
x = 20 rg
x = 25 rg
ż
rses
! /
arb
itrar
y un
its1
10
100
104
105
106
107
r / rg
1 10 100
Extended Source: h = 10rg, 0 < x < 25rg
Point source: h = 10rg, x = 25rg
• Monte Carlo simulation
• Start rays at random locations in random directions
• Varying intensity across source
• Large sample with GPU!
Extended Sources
22
! /
arbi
trar
y un
its
1
1000
106
r / rg
1 10 100
a = 0a = 0.2a = 0.4a = 0.6a = 0.8a = 0.998
! /
arbi
trar
y un
its
0.1
1
10
100
1000
104
105
106
r / rg
1 10 100
a = 0a = 0.2a = 0.4a = 0.6a = 0.8a = 0.998
The Effect of Spin
23
Axial Source, h = 3rg Ring Source, h = 5rg, x = 3rg
• Understand observed emissivity profile in terms of General Relativity
• Simple model produces observed effects
• Constrain X-ray source parameters in 1H 0707-495
• Low height (timing & steep inner emissivity) – within 2rg
• Extended to ~30rg (outer break radius)
Consequences
24
• Follow time of rays, e.g. from disc to observer
Understanding Reverberation
25
1 100.5 2 5
10ï4
10ï3
0.01
0.1
1
norm
aliz
ed c
ount
s sï1
keV
ï1
Energy (keV)
1H 0707-495 in January 2011
26
XMM NewtonEPIC pn
January 2008January 2011
1 100.5 2 5
10ï4
10ï3
0.01
0.1
1
norm
aliz
ed c
ount
s sï1
keV
ï1
Energy (keV)
100 101 102 10310!10
10!8
10!6
10!4
10!2
100
r / rg
! / a
rbitra
ry un
its
January 2011January 2008
1H 0707-495 in January 2011
26
XMM NewtonEPIC pn
January 2008January 2011
! /
arb
itrar
y un
its
10"3
1
106
r / rg
1 10 100
h = 1.235 rg
h = 1.5 rg
h = 2 rg
h = 10 rg
h = 5 rg
Pho
ton
Fra
ctio
n
0
0.2
0.4
0.6
0.8
Source Height / rg
1 10 100
• Compact source, close to axis at h ~ 1.5rg
A change to the source?
27
DiscEscape
28
January 2008 January 2011
• Detailed analysis of X-ray spectra and timing reveals accretion disc emissivity profile
• Systematic theoretical modelling
• Understand observed spectra (and variability)
• Observed profiles explained by GR
• Constraints on source properties
• Era of precision X-ray measurements and understanding the physics of these sources...
Conclusions
29