Impact of intrinsic polarisation of Sgr A* historical flares on (polarisation) properties of their X-ray echoes

Abstract

Reflection of X-ray emission on molecular clouds in the inner $\sim$ 100 pc of our Galaxy reveals that, despite being extremely quiet at the moment, our supermassive black hole Sgr A* should have experienced bright flares of X-ray emission in the recent past. Thanks to the improving characterisation of the reflection signal, we are able to infer parameters of the most recent flare(s) (age, duration and luminosity) and relative line-of-sight disposition of the brightest individual molecular complexes. We show that combining these data with measurements of polarisation in the reflected X-ray continuum will not only justify Sgr A* as the primary source but also allow deriving intrinsic polarisation properties of the flare emission. This will help to identify radiation mechanisms and underlying astrophysical phenomena behind them. For the currently brightest reflecting molecular complex, Sgr A, the required level of sensitivity might be already accessible with upcoming X-ray polarimeters.

7 pages, 4 figures, updated to correspond to the accepted version

References in corpus (13)

• Polarimetry of near-infrared flares from Sagittarius A*
• Variable accretion and emission from the stellar winds in the Galactic centre
• Thermal disc emission from a rotating black hole: X-ray polarization signatures
• Time Dependent Models of Flares from Sagittarius A*
• Discovery of Variable Iron Fluorescence from Reflection Nebulae in the Galactic Center
• Chandra Spectral and Timing Analysis of Sgr A*'s Brightest X-ray Flares
• Polarized light from Sgr A* in the near-infrared $K_s$-band
• Not that long time ago in the nearest galaxy: 3D slice of molecular gas revealed by a 110 years old flare of Sgr A*
• An X-ray survey of the central molecular zone: variability of the Fe Ka emission line
• Prospects of 3D mapping of the Galactic Centre clouds with X-ray polarimetry
• "Failed" tidal disruption events and X-ray flares from the Galactic Center
• Reflection nebulae in the Galactic Center: the case for soft X-ray imaging polarimetry
• ESA Voyage 2050 white paper: A Polarized View of the Hot and Violent Universe

Cited by in corpus (5)

• X-ray polarization evidence for a 200 years-old flare of Sgr A${}^{\ast }$
• SRG/eROSITA view of X-ray reflection in the Central Molecular Zone: a snapshot in September-October 2019
• Prospects for the polarimetric mapping of the Sgr A molecular cloud complex with IXPE
• Radiative energy from a reconnection region around massive black hole
• High Energy Emission from the Galactic Center