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 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 source dust grain oberserver

Scattering and Absorption 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

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= 2  a /

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 N H * 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-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

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

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

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

Halo Modelling For each compound / element :( Mg, Fe, Si, C, SiO 4, SiO 2, Mg 2 SiO 4, Fe 2 SiO 4 ) - 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 (N H ~ 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