X-ray Scattering Halos from the Galactic Center: Implications for Diffuse Emission Around SgrA*

Abstract

We consider the absorption and scattering of X-rays observed from the Galactic center. One objective is to characterize the intrinsic X-ray emission from the central black hole, SgrA*, in its quiescent and flaring states. We correct the fluxes observed by the Chandra and XMM telescopes for absorption and scattering, using realistic models for the dust grain size distribution, gas and dust abundances and spatial distributions. However, there are still large uncertainties. Since much of the intervening dust is close to SgrA*, the scattered halo of X-ray photons is very concentrated: its intensity can dominate the Chandra PSF inside 1", and so affects estimates of the point source flux. It also broadens the radial intensity profiles of Galactic center sources - observations of this effect can help constrain models of the spatial distribution of the dust. We estimate that the combined scattering halos from observed Galactic center sources within 10" of SgrA* contribute up to ~10% of the observed diffuse emission in this region. Dust-scattered photons suffer a time delay relative to the photons that arrive directly. For dust that is 100 pc towards us from the Galactic center, this delay is about 1000 s at angles of 1", and 100 ks at 10". We illustrate how the evolution of the scattering halo following X-ray flares from SgrA* or other sources can also help to constrain the dust's line of sight distribution. We discuss the implications of X-ray scattering halos for the intensity of diffuse emission that has been reported within a few arcseconds of SgrA*: in the most extreme, yet viable, model we consider, ~1/3 of it is due to dust scattering of an unresolved source. The remainder results from an extended source of emission.

arXiv comment24 pages, including 10 figures, ApJ accepted

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• The Spectra and Variability of X-ray Sources in a Deep Chandra Observation of the Galactic Center
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• A Remarkable Low-Mass X-ray Binary within 0.1 pc of the Galactic Center
• A Persistent High-Energy Flux from the Heart of the Milky Way : Integral's view of the Galactic Center
• A Search for New Galactic Magnetars in Archival Chandra and XMM-Newton Observations
• Star-forming accretion flows and the low luminosity nuclei of giant elliptical galaxies
• Sgr A* in context: daily flares as a probe of the fundamental X-ray emission process in accreting black holes
• Probing the Interstellar Dust towards the Galactic Centre: Dust Scattering Halo around AX J1745.6-2901
• Probing the Spatial Distribution of the Interstellar Dust Medium by High Angular Resolution X-ray Halos of Point Sources
• Spectral properties of Three-dimensional Magneto-hydrodynamical Accretion Flows
• Ray-tracing simulations and spectral models of X-ray radiation in dusty media
• The 2013 outburst of a transient very faint X-ray binary, 23" from Sgr A*
• Near-infrared counterparts of Chandra X-ray sources toward the Galactic Center
• Our Supermassive Black Hole Rivaled the Sun in the Ancient X-ray Sky