Highlights from X-Ray Grating Spectroscopy

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HighlightsfromX-Ray Grating Spectroscopy

• Cambridge MA July 2007
• Ehud Behar
• Department of Physics, Technion, ISRAEL

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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

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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
  beyond-thermal flows rotation, turbulence,
  flare distribution?

(Chung et al. 2004)
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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 dayX-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
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Spatially Resolved Spectroscopy

• Giant elliptical galaxyNGC 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, constrainingvturb 30 km/s (or
  scattering would be quenched)
• order of magnitude better than instrumental
  resolution

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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)
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Where is the X-ray plasma?UV destruction of
forbidden lines

• UV flux depletes the long-lived 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
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Finding Unseen Companionswith UV Depletion Effect
? Lep B
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? Lep Astrometry
? Lep
? Lep B
radio
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Where is the X-Ray Absorber? Recombination/Ionizat
ion 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)
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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

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Type-2 AGN Discrete Emission from Photoionized
Plasma

• NGC 1068
• RGS

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Line Emission Sensitive to Column Density Effect

• Lines are driven by recombination (cascades) and
  by photoexcitation
• Resonance cross sections are much higher, but
• Resonance absorption saturates gt photoexcit.
  diminishes while recombination persists
• Consequently, resonance lines dominate low NH
  regions (base of ionization cone)
• Forbidden lines dominate high NH regions
• Can intermediate line ratios mimic collisional
  plasma?not at high S/N
• The resulting Seyfert 2 spectrum includes entire
  range gt use average in model

Absorption Emission
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Emission Line Ratios Sensitive to Column Density
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Not Only NGC 1068

• dozens of additional sources
• O VII column densities comparable to the Seyfert
  1 direct-absorption 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
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Recombination Spectra in Planetary Nebulae?
300 ks LETG observation of BD30 PI J. Kastner,
plot by R. Nordon, see talk by Young Sam Yu
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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

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Five Orders of Magnitude in Ionization Parameter
Ability to see the full ionization range reveals
exactly where thermal instability occurs
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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
• 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 gt
  associating Seyfert 1 absorber with Seyfert 2
  emitter
• Thermal instability in AGN outflows
• Of course, there are many other exciting examples

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Many thanks to my collaborators over the years
and to my students at the Technion
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THANK YOU FOR YOUR ATTENTION
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Cooling Curves
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