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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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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
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
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