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