Reflection nebulae in the Galactic Center: the case for soft X-ray imaging polarimetry

Abstract

The origin of irradiation and fluorescence of the 6.4 keV bright giant molecular clouds surrounding Sgr A*, the central supermassive black hole of our Galaxy, remains enigmatic. Testing the theory of a past active period of Sgr A* requires X-ray polarimetry. In this paper, we show how modern imaging polarimeters could revolutionize our understanding of the Galactic Center. Through Monte Carlo modeling, we produce a 4-8 keV polarization map of the Galactic Center, focusing on the polarimetric signature produced by Sgr B1, Sgr B2, G0.11-0.11, Bridge E, Bridge D, Bridge B2, MC2, MC1, Sgr C3, Sgr C2, and Sgr C1. We estimate the resulting polarization, include polarized flux dilution by the diffuse plasma emission detected toward the GC, and simulate the polarization map that modern polarimetric detectors would obtain assuming the performances of a mission prototype. The eleven reflection nebulae investigated in this paper present a variety of polarization signatures, ranging from nearly unpolarized to highly polarized (about 77%) fluxes. A major improvement in our simulation is the addition of a diffuse, unpolarized plasma emission that strongly impacts soft X-ray polarized fluxes. The dilution factor is in the range 50% - 70%, making the observation of the Bridge structure unlikely even in the context of modern polarimetry. The best targets are the Sgr B and Sgr C complexes, and the G0.11-0.11 cloud. An exploratory observation of a few hundred kilo-seconds of the Sgr B complex would allow a significant detection of the polarization and be sufficient to derive hints on the primary source of radiation. A more ambitious program (few Ms) of mapping the giant molecular clouds could then be carried out to probe with great precision the turbulent history of Sgr A*, and place important constraints on the composition and three-dimensional position of the surrounding gas.

arXiv comment7 pages, 3 figures, 2 tables, accepted for publication in A&A

References in corpus (37)

• Measuring Distance and Properties of the Milky Way's Central Supermassive Black Hole with Stellar Orbits
• Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre
• A 100-parsec elliptical and twisted ring of cold and dense molecular clouds revealed by Herschel around the Galactic Center
• An efficient photoelectric X-ray Polarimeter for the study of Black Holes and Neutron Stars
• The disc instability model for X-ray transients: evidence for truncation and irradiation
• What controls star formation in the central 500 pc of the Galaxy?
• The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline
• Discrete sources as the origin of the Galactic X-ray ridge emission
• XMM-Newton observation of the brightest X-ray flare detected so far from SgrA*
• Discovery of a superluminal Fe K echo at the Galactic Center: The glorious past of Sgr A* preserved by molecular clouds
• An Overabundance of Transient X-ray Binaries within 1 pc of the Galactic Center
• Iron and Nickel Line Diagnostics for the Galactic Center Diffuse Emission
• Chandra-HETGS Observations of the Brightest Flare Seen from Sgr A*
• 9.7 um Silicate Features in AGNs: New Insights into Unification Models
• Modeling optical and UV polarization of AGNs I. Imprints of individual scattering regions
• X-ray hiccups from SgrA* observed by XMM-Newton. The second brightest flare and three moderate flares caught in half a day
• Equivalent width, shape and proper motion of the iron fluorescent line emission from the molecular clouds as an indicator of the illuminating source X-ray flux history
• Echoes of multiple outbursts of Sagittarius A* revealed by Chandra
• On the Origin of the Iron K Line in the Spectrum of the Galactic X-ray Background
• Modeling optical and UV polarization of AGNs II. Polarization imaging and complex reprocessing
• Chandra Observations of Diffuse X-Rays from the Sagittarius B2 Cloud
• The Origin of X-ray Emission from a Galactic Center Molecular Cloud: Low Energy Cosmic Ray Electrons
• Light bending scenario for accreting black holes in X-ray polarimetry
• X-ray Echo from the Sagittarius C Complex and 500-year Activity History of Sagittarius A*
• Gas Pixel Detectors for X-ray Polarimetry applications
• The X-ray lightcurve of Sgr A* over the past 150 years inferred from Fe-Ka line reverberation in Galactic Centre molecular clouds
• ASCA Discovery of Diffuse 6.4 keV Emission Near the Sgr C Complex: A New X-ray Reflection Nebula
• Polarization of X-ray emission from the Sgr B2 cloud
• An X-Ray Face-on View of the Sgr B Molecular Clouds Observed with Suzaku
• The imaging properties of the Gas Pixel Detector as a focal plane polarimeter
• Spectral and polarimetric characterization of the Gas Pixel Detector filled with dimethyl ether
• Fe Ka line emission from the Arches cluster region - evidence for ongoing particle bombardment?
• Broad iron emission lines in Seyfert Galaxies - re-condensation of gas onto an inner disk below the ADAF
• X-ray Polarimetry: a new window on the high energy sky
• Prospects of 3D mapping of the Galactic Centre clouds with X-ray polarimetry
• The Galactic Center: Not an Active Galactic Nucleus
• X-ray polarization fluctuations induced by cloud eclipses in active galactic nuclei

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• Prospects for IXPE and eXTP polarimetric archaeology of the reflection nebulae in the Galactic center
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