Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1

H. Krawczynski, Fabio Muleri, Michal Dovčiak, Alexandra Veledina, Nicole Rodriguez Cavero, Jiří Svoboda, Adam Ingram, G. Matt, Javier A. García, Vladislav Loktev

Abstract

A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto a black hole, which heats the gas sufficiently to emit x-rays. We report a polarimetric observation of the XRB Cygnus X-1 using the Imaging x-ray Polarimetry Explorer. The electric field position angle aligns with the outflowing jet, indicating that the jet is launched from the inner x-ray emitting region. The polarization degree is (4.01+-0.20)% at 2 to 8 kiloelectronvolts, implying that the accretion disk is viewed closer to edge-on than the binary orbit. The observations reveal that hot x-ray emitting plasma is spatially extended in a plane perpendicular to the jet axis, not parallel to the jet.

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