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X-ray Absorption and Scattering by Interstellar Dust: the XMM view

X-ray Absorption and Scattering by Interstellar Dust: the XMM view

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X-ray Absorption and Scattering by Interstellar Dust: the XMM view

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  1. X-ray Absorption and Scattering by Interstellar Dust: the XMM view Elisa 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

  2. scattering in 4p • scattering dominant in Vis. Reddened stars  Extinction = Absorption + Scattering Both components of extinction CANNOT be separated Extinction from IR to Far-UV

  3. dust grain • small angle scattering • X-ray sources surrounded by haloes oberserver source Both components of extinction CAN be separated 40° Extinction in X-rays

  4. Scattering grain size distribution distribution along line of sight grain number density distance determination Absorption total column density (metals: C,O,Fe,Si...) Scattering + Absorption  physical state of grains chemistry of grains Scattering and Absorption

  5. ID Scattering theory a = grain size X= 2p a / l l = wavelenght of incident radiation Rayleigh-Gans approximation Differential Scattering cross section: Often violated in X-ray band ! Exact Mie Theory

  6. 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 XMM & Chandra

  7. 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

  8. XMM Observation of Cyg X-2 Imaging 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

  9. 0.5-2 keV 6-8 keV Cyg X-2 Spectral Analysis (1)

  10. Comparison with an halo free source: PKS 0558-504 Cyg X-2 PKS 0558-504 Cyg X-2 Spectral Analysis (2)

  11. The Scattered Radiation Comparison between Rayleigh Gans Approximation and exact Mie Theory (Smith & Dwek 1998)

  12. For 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 (Weingartner & Draine 2001) - Distributed according to MRN model and WD model - Best fit through c2minimization Costantini et al 2003 in prep Halo Modelling

  13. - 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) Extinction by ID

  14. 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