AC1 - Spectral and Temporal properties of Black Holes and neutron stars and the theoretical models |
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Speaker |
Taverna, Roberto |
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Coauthors |
Taverna, Roberto; Dovciak, Michal; Matt, Giorgio; Zhang, Wenda |
| Talk Title |
Polarization Of Emission From Black Holes Accretion Disk: Including Returning Radiation |
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Abstract |
Accretion disks around stellar-mass black holes (BHs) are observed to emit radiation peaking in the X-rays (at about 1 keV) when the source is in the thermal state. This emission is expected to be polarized, because of electron scattering in the disk, with a linear polarization fraction up to 12 percents, depending on the inclination angle (Chandrasekhar, 1960). Photons will experience a rotation of the polarization plane due to General Relativity effects (Connors & Stark, 1977, Stark & Connors, 1977, Ishihara et al., 1988). X-ray polarization measurements can be then crucial in assessing strong gravity effects around accreting stellar-mass BHs, providing independent constraints on their spin. Such kind of measurements should be within reach of the new-generation X-ray polarimeters like IXPE (recently approved by NASA and scheduled to be launched in 2021) and eXTP (approved by Chinese Academy of Sciences). In this work, we present a model for simulating the spectral and polarization properties of X-ray radiation emitted by the accretion disk. Starting from the model developed by Dovciak et al. (2008), we incorporate the contribution of returning radiation, i.e. of photons that are deflected back to the disk before they eventually reach the observer. We develop a specific code to calculate the change in polarization angle for photons traveling between two different locations in the disk, accounting for absorption by the disk material. |
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