Highlights from x ray grating spectroscopy
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Highlights from X-Ray Grating Spectroscopy. Cambridge MA July 2007 Ehud Behar Department of Physics, Technion, ISRAEL. Outline. Choice of Topics things you might not have thought you could measure - a biased view Spectral line profiles gas kinematics beyond instrumental resolution

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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


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


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)


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


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


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)


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


Finding Unseen Companionswith UV Depletion Effect

 Lep B


 Lep Astrometry

 Lep

 Lep B

radio


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)


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


NGC 1068

RGS

Type-2 AGN: Discrete Emission from Photoionized Plasma


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 => 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 => use average in model

Absorption Emission


Emission Line Ratios Sensitive to Column Density


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


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


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


Five Orders of Magnitude in Ionization Parameter

Ability to see the full ionization

range reveals exactly where

thermal instability occurs


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 starsleading 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


Many thanks to my collaborators over the years and to my students at the Technion


THANK YOU FOR YOUR ATTENTION


Cooling Curves


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