Highlights
from
X-Ray Grating Spectroscopy
Cambridge MA July 2007
Ehud Behar
Department of Physics, Technion, ISRAEL
1
Outline
•
Choice of Topics
– things you might not have thought you could measure - a biased view
•
Spectral line profiles
– gas kinematics
– beyond instrumental resolution
•
Where is the X-ray plasma?
– distances from UV sources
– spectral variability
•
Measuring column density with emission lines
– in AGN
– in PN
•
•
Observing thermal instabilities from inner-shell phenomena
Concluding Remarks
2
Exploiting the
High Spectral Resolution
• Algol: (eclipsing) stellar
binary B8 V + K2 IV
•
“Where is the X-ray stuff ?“
• Doppler shifts accurate to
±50 km/s reveal the X-ray
source: Algol B
– B8 not X-ray source
• Excessive Doppler widths
(125 km/s) reveal beyondthermal flows:
rotation, turbulence, flare
distribution?
(Chung et al. 2004)
3
X-Ray Flows in  Carinae?
•
•
•
•
•
Massive LBV
Steady X-rays consistent with
a colliding-winds binary with a
5.54 yr orbit (Corcoran et al. 2001)
Not so the intriguing ~70 day
X-ray shut down (minimum)
around periastron passage,
nor the preceding bright
flares
Gratings: Velocity shifts and
broadening during flares as
system approaches periastron
Can not be accounted for by
continuous wind collision and
orientation effects
(but see poster by M. Corcoran)
Wind-wind model profiles
by Henley et al. 2003
4
Spatially Resolved Spectroscopy
•
•
•
•
•
Giant elliptical galaxy
NGC 4636
Cross-dispersion
line-ratio variation
Resonant scattering reduces
Fe XVII f / r line ratio away
from center
MC fit (by J. Peterson)
follows photons as they
scatter, constraining
vturb ≤ 30 km/s (or scattering
would be quenched)
… order of magnitude better
than instrumental resolution
5
Opposite Effect?
• NGC 253 with RGS
• forbidden line
enhanced away from
center
• Hard to explain, but
demonstrates again
the performance of
the gratings
Bauer et al. (2007)
6
Where is the X-ray plasma?
UV destruction of forbidden lines
• UV flux depletes the longlived upper levels of
forbidden lines
(e.g., He-like triplets)
• Hence, f / i ratios
sensitively probe distance
from UV source
• Applied to O star winds
(e.g.,  Pup) - see talk by
A. Pollock and poster by
M. Leutenegger
• Easily confused with
density effect
Kahn et al. 2001
r
i
f
7
Finding Unseen Companions
with UV Depletion Effect
 Lep B
8
 Lep Astrometry
 Lep
 Lep B
radio
9
Where is the X-Ray Absorber?
Recombination/Ionization Time Scales
•
•
•
Reaction of absorber to
increase/decrease of ionizing
flux is sensitive to
ionization/ recombination
times
Ionization/recombination
times yield distance/density
(=L/nr2) of absorber from
ionization source
Current grating
spectrometers allow for
detection of variations on
t ≥ days, even for the
brightest sources
t ~ days
t ~ months (Krongold et al. 2005)
10
Outline
•
Choice of Topics
–
•
Spectral line profiles
–
–
•
distances from UV sources
spectral variability
Measuring column density with emission lines
–
–
•
•
gas kinematics
beyond instrumental resolution
Where is the X-ray plasma?
–
–
•
things you might not have thought you could measure - a biased view
in AGN
in PN
Observing thermal instabilities from inner-shell phenomena
Concluding Remarks
11
Type-2 AGN: Discrete Emission from
Photoionized Plasma
NGC 1068
RGS
12
Line Emission Sensitive to
Column Density Effect
•
•
•
•
•
•
•
Lines are driven by recombination
(cascades) and by photoexcitation
Absorption
Emission
Resonance cross sections are
much higher, but …
Resonance absorption saturates
=> photoexcit. diminishes while average flux along cone
recombination persists
 E 
  E 
Consequently, resonance lines
1
1
e
dominate low NH regions
F E 
F0e t dt  F0
(base of ionization cone)
E 0
E
Forbidden lines dominate
high NH regions
Can intermediate line ratios mimic
collisional plasma?
not at high S/N
 2 spectrum
The resulting Seyfert
includes entire range =>
use average in model
 
 

 
13
Emission Line Ratios
Sensitive to Column Density
f/r
10
e
H e / r
H e / r
f
H e / r
1
H e / r
rrc
rrc / r
i
f
H e

0.1
NGC 1068:
Flux ratio (relative to r)
collisional:
O +6 at kT =5eV
i/r
0.01
10 1 5
10 1 6
10 1 7
10 1 8
10 1 9
10 2 0
10 2 1
i
H e


10 2 2
Ionic Colum n D ensity (cm -2 )
Behar, K inkhabw ala, Sako, et al. 2001
14
Not Only NGC 1068
• ~ dozens of additional
sources
• O VII column densities
comparable to the
Seyfert 1 directabsorption measurements
• Supports AGN unified
scheme:
X-ray narrow line region
• Interesting question: What
makes all the sources lie on
such a tight correlation ?
Guainazzi & Bianchi 2007
15
Recombination Spectra in
Planetary Nebulae?
300 ks LETG observation of BD+30
PI J. Kastner, plot by R. Nordon, see talk by Young Sam Yu
16
Outline
•
Choice of Topics
–
•
Spectral line profiles
–
–
•
distances from UV sources
spectral variability
Measuring column density with emission lines
–
–
•
•
gas kinematics
beyond instrumental resolution
Where is the X-ray plasma?
–
–
•
things you might not have thought you could measure - a biased view
in AGN
in PN
Observing thermal instabilities from inner-shell phenomena
Concluding Remarks
17
Five Orders of Magnitude in
Ionization Parameter
Ability to see the full ionization
range reveals exactly where
thermal instability occurs
18
CONCLUDING REMARKS
•
•
•
•
•
•
Spectroscopy is where the physics is!
Grating spectroscopy has boosted X-Ray Astronomy to level with other
branches of astronomy and contributed to all fields of astrophysics
The high spectral resolution has provided unprecedented plasma diagnostics
In the future we should aim at better time- and space- resolved spectra
A “highlight” talk does not provide the full picture but …
Nevertheless, some less conventional diagnostics with gratings:
–
–
–
–
•
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Kinematics: Discerning binary and non-thermal motion,
including turbulence width better than spectral resolution
UV sensitive X-ray lines: Distance from OB stars
leading to the discovery of B star companions
Distinguishing between AGN and starburst line emission
Measuring column densities in emission =>
associating Seyfert 1 absorber with Seyfert 2 emitter
Thermal instability in AGN outflows
Of course, there are many other exciting examples
19
Many thanks to my collaborators over
the years and to my students at the
Technion
20
THANK YOU
FOR YOUR ATTENTION
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22
Cooling Curves
n 2  net  n 2  rad  n 2  IC  nPI

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