X-ray Absorption and Scattering by Interstellar Dust: the XMM view Elisa Costantini Max Planck...
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Transcript of X-ray Absorption and Scattering by Interstellar Dust: the XMM view Elisa Costantini Max Planck...
X-ray Absorption and Scattering by Interstellar Dust:
the XMM viewElisa Costantini
Max Planck Institute for extraterrestrial Physics (MPE)
P. Predehl, J. Trümper, G. Hasinger, M.Freyberg, N. Schulz (MIT)
XMM-EPIC consortium meeting Palermo 14-16 Sept 2003
Extinction from IR to Far-UV
Reddened stars Extinction = Absorption + Scattering
• scattering in 4• scattering dominant in Vis.
Both components of extinction CANNOT be separated
Extinction in X-rays
40°
• small angle scattering• X-ray sources surrounded by haloes
Both components of extinction CAN be separated
sca
x
source
dust grain
oberserver
Scattering and Absorption
Scattering grain size distributiondistribution along line of sightgrain number densitydistance determination
Absorption total column density (metals: C,O,Fe,Si...)
Scattering + Absorption physical state of grains chemistry of grains
ID Scattering theory
a = grain size
= wavelenght of incident radiation
Rayleigh-Gans approximation
Differential Scattering cross section:
Often violated in X-ray band !
Exact Mie Theory
X= 2a /
XMM & Chandra•high resolution imaging (0.5'') + broad band spectroscopy Chandra-ACIS-S:
energy dependence of the halo shape constraints on the grain models distance determination
* high sensitivity imaging + spectroscopy XMM-Newton
fainter haloes, lower energies, lower NH
* high resolution spectroscopy Chandra-HETGS, (LETGS) ID composition and abundances
Technical Limitations
Bright fluxes imply strong PILE UP:
• Distortion of surface brightness profiles hampering in flight calibration of PSF & loss of information on the scattering halo • Incorrect determination of the flux additional errors in the comparison halo-PSF
XMM Observation of Cyg X-2Imaging technical details:- vignetting corrected- exposure corrected - annuli of ~0.6' ranging from 0.8' to 4' - central region avoided because of pileup- RAWY > 180 to use only Y9 response matrix- trailed events cut out
Spectral analysis:- cut on the Out of Time events to avoid pile up in the central column
- Information on the Flux lost- Recovered Cyg X-2 spectrum
Cyg X-2 Spectral Analysis (2)
Comparison with an halo free source: PKS 0558-504
PKS 0558-504 Cyg X-2
The Scattered RadiationComparison between Rayleigh Gans Approximation and exact Mie Theory
(Smith & Dwek 1998)
Halo ModellingFor each compound / element:(Mg, Fe, Si, C, SiO4, SiO2, Mg2SiO4, Fe2SiO4)
- Density- Energy dependent refractive index- Calculated scattered intensity for each Energy and grain size using the complete Mie theory
- Distributed according to MRN model and WD model - Best fit through minimization
Costantini et al 2003 in prep
(Weingartner & Draine 2001)
Extinction by ID
- There is no evidence of Mg and Si in the absorbed spectrum of Cyg X-2
(NH~2 1021 cm-2)
(Draine et al 2003)
Summary- XMM spectral resolution is suitable for the study of scattering features- Successful detection in Cyg X-2!
- Oxigen, Magnesium, Silicon clearly detected- Standard grain size distribution models satisfactorily fit the data, in first approximation.
Future:- Identification of the scattering compounds- Constraints on grain size distribution- Chemistry of ID towards different line of sights in the Milky Way