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

Krawczynski, H.; Muleri, F.; Dovciak, M.; Veledina, A.; Cavero, N. R.; Svoboda, J.; Ingram, A.; Matt, G.; Garcia, J. A.; Loktev, V.; Negro, M.; Poutanen, J.; Kitaguchi, T.; Podgorny, J.; Rankin, J.; Zhang, W.; Berdyugin, A.; Berdyugina, S. V.; Bianchi, S.; Blinov, D.; Capitanio, F.; Di Lalla, N.; Draghis, P.; Fabiani, S.; Kagitani, M.; Kravtsov, V.; Kiehlmann, S.; Latronico, L.; Lutovinov, A. A.; Mandarakas, N.; Marin, F.; Marinucci, A.; Miller, J. M.; Mizuno, T.; Molkov, S. V.; Omodei, N.; Petrucci, P. -O.; Ratheesh, A.; Sakanoi, T.; Semena, A. N.; Skalidis, R.; Soffitta, P.; Tennant, A. F.; Thalhammer, P.; Tombesi, F.; Weisskopf, M. C.; Wilms, J.; Zhang, S.; Agudo, I.; Antonelli, L. A.; Bachetti, M.; Baldini, L.; Baumgartner, W. H.; Bellazzini, R.; Bongiorno, S. D.; Bonino, R.; Brez, A.; Bucciantini, N.; Castellano, S.; Cavazzuti, E.; Ciprini, S.; Costa, E.; De Rosa, A.; Del Monte, E.; Di Gesu, L.; Di Marco, A.; Donnarumma, I.; Doroshenko, V.; Ehlert, S. R.; Enoto, T.; Evangelista, Y.; Ferrazzoli, R.; Gunji, S.; Hayashida, K.; Heyl, J.; Iwakiri, W.; Jorstad, S. G.; Karas, V.; Kolodziejczak, J. J.; La Monaca, F.; Liodakis, I.; Maldera, S.; Manfreda, A.; Marscher, A. P.; Marshall, H. L.; Mitsuishi, I.; C. -Y., Ng; O'Dell, S. L.; Oppedisano, C.; Papitto, A.; Pavlov, G. G.; Peirson, A. L.; Perri, M.; Pesce-Rollins, M.; Pilia, M.; Possenti, A.; Puccetti, S.; Ramsey, B. D.; Romani, R. W.; Sgro, C.; Slane, P.; Spandre, G.; Tamagawa, T.; Tavecchio, F.; Taverna, R.; Tawara, Y.; Thomas, N. E.; Trois, A.; Tsygankov, S.; Turolla, R.; Vink, J.; Wu, K.; Xie, F.; Zane, S.

doi:10.1126/science.add5399

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. These observations reveal that hot x-ray–emitting plasma is spatially extended in a plane perpendicular to, not parallel to, the jet axis.