Intro/Motivation Thermal State Hard State Applications Discussion
X-ray Polarization: The Dawn of a New Age inBlack Hole Astrophysics
Jeremy Schnittman
Johns Hopkins University
Einstein Fellows SymposiumHarvard CfA, October 27, 2009
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
GEMS: Gravity and Extreme Magnetism SMEX
Approved for “phase A” funding in recent round of SMEXproposals
Sensitive down to . 1% at 1 milliCrab (106 s exposure)
Energy bandwidth of 2-10 keV
Energy resolution of 2 keV
If approved, could launch in 2012
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
GEMS: Gravity and Extreme Magnetism SMEX
Selected for full funding in recentround of SMEX proposals
Sensitive down to . 1% at 1 milliCrab(106 s exposure)
Energy bandwidth of 2-10 keV
Energy resolution of ∼ 2 keV
If Now approved, could will launch in2012 2015 2014
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
GEMS: Gravity and Extreme Magnetism SMEX
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Description of model
disk parameters:
BH mass MBH spin a/Maccretion rate M/MEdd
emissivity profile
corona parameters:
temperature, density profile Tc(r), ρc(r)coronal geometry (sandwich, clumpy, sphere, etc.)optical depth to Compton scattering τes
observer parameters:
inclinationdistance to source
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Plane polarization from a thermal disk is rotated byrelativistic beaming and gravitational lensing
M = 10M�
N-T emission
L = 0.1LEdd
deg=5%
D = 40M
10-5
10-4
10-3
10-2
10-1
1
I/Im
ax
i=75o0.1 1.0 10.0
Eobs
(keV)
0.1
1.0
10.0
pola
rizat
ion
degr
ee (%
)
i=45o
i=60o
i=75o
a/m = 0a/m = 0.9
0.1 1.0 10.0E
obs (keV)
-80
-60
-40
-20
0
pola
rizat
ion
angl
e (d
eg)
a/m = 0a/m = 0.9
i=45o
i=60o
i=75o
(cf. Connors et al. 1980)X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Return radiation near the BH changes the polarizationsignature significantly
direct only
deg=5%
D = 40M
10-5
10-4
10-3
10-2
10-1
1
I/Im
ax
i=75o
direct+return
deg=5%
D = 40M
10-5
10-4
10-3
10-2
10-1
1
I/Im
axi=75o
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Return radiation near the BH changes the polarizationsignature significantly
M = 10M� a/M = 0.9 L = 0.1LEdd
0.1 1.0 10.0E
obs (keV)
0.1
1.0
10.0
pola
rizat
ion
degr
ee (%
)
i = 75o
i = 60o
i = 45o
direct onlydirect+reflected
0.1 1.0 10.0E
obs (keV)
-100
-50
0
50
pola
rizat
ion
angl
e (d
eg)
i = 75o
i = 60o
i = 45o
direct onlydirect+reflected
JS & Krolik (2009a)
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Polarization in thermal state can be used to measure BHspin
M = 10M� i = 75◦ L = 0.1LEdd
0.1 1.0 10.0E
obs (keV)
0.1
1.0
10.0
pola
rizat
ion
degr
ee (%
)
a/M=0 0.5 0.9 0.99 0.998
0.1 1.0 10.0E
obs (keV)
-100
-50
0
50
pola
rizat
ion
angl
e (d
eg)
a/M=0 0.5 0.9 0.99 0.998
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Hard X-rays come from inverse-Compton scattering in ahot corona
0.1 1.0 10.0 100.0 1000.0E
obs (keV)
0.1
1.0
10.0
100.0
Inte
nsity
(νI ν) total
thermal
upscattered
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Scattering through optically thin corona rotates netpolarization angle
e.g. Sunyaev & Titarchuk (1985)
Haardt & Matt (1993)
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Corona scattering preferentially changes polarization angleof high-energy photons
M = 10M� a/M = 0.9 Lseed = 0.1LEdd
0.1 1.0 10.0E
obs (keV)
0.1
1.0
10.0
degr
ee (%
)
i = 75o
i = 60o
i = 45o
direct onlydirect+scattered
0.1 1.0 10.0E
obs (keV)
-100
-50
0
50
100
pola
rizat
ion
angl
e (d
eg)
i = 75o
i = 60o
i = 45o
direct onlydirect+scattered
JS & Krolik (2009b)
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Polarization as probe of coronal properties
M = 10M� i = 75◦ Lseed = 0.1LEdd
0.1 1.0 10.0E
obs (keV)
0.1
1.0
10.0
pola
rizat
ion
degr
ee (%
)
τes=2.0, Tcor
=50 keVτes=1.0, T
cor=100 keV
τes=0.5, Tcor
=200 keV
0.1 1.0 10.0E
obs (keV)
-100
-50
0
50
100
pola
rizat
ion
angl
e (d
eg)
τes=2.0, Tcor
=50 keVτes=1.0, T
cor=100 keV
τes=0.5, Tcor
=200 keV
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
clumpy coronas
0.1 1.0 10.0E
obs (keV)
0.1
1.0
10.0
pola
rizat
ion
degr
ee (%
)
ρclump/ρavg=1ρclump/ρavg=3ρclump/ρavg=10
0.1 1.0 10.0E
obs (keV)
-100
-50
0
50
100
pola
rizat
ion
angl
e (d
eg)
ρclump/ρavg=1ρclump/ρavg=3ρclump/ρavg=10
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Applications/Future Work
New polarization measurements will allow us toprobe plunging regionestimate coronal propertiesinfer emissivity profiles (Fe Kα lines)measure BH spinmeasure geometry of accretion flow in NS’s
3-D numerical MHD simulations (Noble, Krolik, & Hawley 2008)
develop realistic heating, cooling functionsdefine electron temperature everywhereself-consistently calculate inverse-Compton spectrum andpolarization
Fitting observationsGreen’s function-type transferorthogonal basis of fitting functions to minimize parameterdegeneracyfold through GEMS response function, develop XSPECpackages for data analysis
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Emissivity in the plunging region
Inside the ISCO, the gas follows geodesic trajectories determinedby E and ` at the ISCO, yet with (possibly) non-zero emissivity.
1 10 100R (M)
0.001
0.010
0.100
1.000
10.000
100.000
loca
l flu
x
NTα=-2
α=0
α=2HARM3D
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Emission inside ISCO reduces sensitivity on spin
“quasi-Newtonian” emissivity (I ∼ r−3 inside ISCO)
0.1 1.0 10.0E
obs (keV)
0.1
1.0
10.0
pola
rizat
ion
degr
ee (%
)
a/M=0 0.5 0.9 0.99 0.998
0.1 1.0 10.0E
obs (keV)
-100
-50
0
50
pola
rizat
ion
angl
e (d
eg)
a/M=0 0.5 0.9 0.99 0.998
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Degeneracy between spin and emission profile
“first-generation” polarimeter: δ ∼ 1%, ∆E/E ∼ 1(contours are 1σ confidence intervals)
0 0.9 0.99 0.999spin a/M
-Inf
-1.8
0.25
1.5
2.3
3.0
α X
0 0.9 0.99 0.999spin a/M
-Inf
-1.8
0.25
1.5
2.3
3.0
α
X
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
Spectropolarimeter on IXO could greatly improve spinmeasurements
“next-generation” polarimeter: δ ∼ 0.3%, ∆E/E ∼ 0.1
0 0.9 0.99 0.999spin a/M
-Inf
-1.8
0.25
1.5
2.3
3.0
α X
0 0.9 0.99 0.999spin a/M
-Inf
-1.8
0.25
1.5
2.3
3.0
α
X
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
Intro/Motivation Thermal State Hard State Applications Discussion
spherical coronas
0.1 1.0 10.0E
obs (keV)
0.1
1.0
10.0
pola
rizat
ion
degr
ee (%
)
Rin=5M
Rin=10M
Rin=15M
Rin=20M
0.1 1.0 10.0E
obs (keV)
-100
-50
0
50
100
pola
rizat
ion
angl
e (d
eg)
Rin=5M
Rin=10M
Rin=15M
Rin=20M
X-ray Polarization: The Dawn of a New Age in Black Hole Astrophysics Jeremy Schnittman
