TY - JOUR

T1 - An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing

AU - Steiner, James F.

AU - Nathan, Edward

AU - Hu, Kun

AU - Krawczynski, Henric

AU - Dovčiak, Michal

AU - Veledina, Alexandra

AU - Muleri, Fabio

AU - Svoboda, Jiri

AU - Alabarta, Kevin

AU - Parra, Maxime

AU - Bhargava, Yash

AU - Matt, Giorgio

AU - Poutanen, Juri

AU - Petrucci, Pierre-Olivier

AU - Tennant, Allyn F.

AU - Baglio, M. Cristina

AU - Baldini, Luca

AU - Barnier, Samuel

AU - Bhattacharyya, Sudip

AU - Bianchi, Stefano

AU - Brigitte, Maimouna

AU - Cabezas, Mauricio

AU - Cangemi, Floriane

AU - Capitanio, Fiamma

AU - Casey, Jacob

AU - Rodriguez Cavero, Nicole

AU - Castellano, Simone

AU - Cavazzuti, Elisabetta

AU - Chun, Sohee

AU - Churazov, Eugene

AU - Costa, Enrico

AU - Di Lalla, Niccolò

AU - Di Marco, Alessandro

AU - Egron, Elise

AU - Ewing, Melissa

AU - Fabiani, Sergio

AU - García, Javier A.

AU - Green, David A.

AU - Grinberg, Victoria

AU - Hadrava, Petr

AU - Ingram, Adam

AU - Kaaret, Philip

AU - Kislat, Fabian

AU - Kitaguchi, Takao

AU - Kravtsov, Vadim

AU - Kubátová, Brankica

AU - La Monaca, Fabio

AU - Latronico, Luca

AU - Loktev, Vladislav

AU - Malacaria, Christian

AU - Marin, Frédéric

AU - Marinucci, Andrea

AU - Maryeva, Olga

AU - Mastroserio, Guglielmo

AU - Mizuno, Tsunefumi

AU - Negro, Michela

AU - Omodei, Nicola

AU - Podgorný, Jakub

AU - Rankin, John

AU - Ratheesh, Ajay

AU - Rhodes, Lauren

AU - Russell, David M.

AU - Šlechta, Miroslav

AU - Soffitta, Paolo

AU - Spooner, Sean

AU - Suleimanov, Valery

AU - Tombesi, Francesco

AU - Trushkin, Sergei A.

AU - Weisskopf, Martin C.

AU - Zane, Silvia

AU - Zdziarski, Andrzej A.

AU - Zhang, Sixuan

AU - Zhang, Wenda

AU - Zhou, Menglei

AU - Agudo, Iván

AU - Antonelli, Lucio A.

AU - Bachetti, Matteo

AU - Baumgartner, Wayne H.

AU - Bellazzini, Ronaldo

AU - Bongiorno, Stephen D.

AU - Bonino, Raffaella

AU - Brez, Alessandro

AU - Bucciantini, Niccolò

AU - Chen, Chien-Ting

AU - Ciprini, Stefano

AU - De Rosa, Alessandra

AU - Del Monte, Ettore

AU - Di Gesu, Laura

AU - Donnarumma, Immacolata

AU - Doroshenko, Victor

AU - Ehlert, Steven R.

AU - Enoto, Teruaki

AU - Evangelista, Yuri

AU - Ferrazzoli, Riccardo

AU - Gunji, Shuichi

AU - Hayashida, Kiyoshi

AU - Heyl, Jeremy

AU - Iwakiri, Wataru

AU - Jorstad, Svetlana G.

AU - Karas, Vladimir

AU - Kolodziejczak, Jeffery J.

AU - Liodakis, Ioannis

AU - Maldera, Simone

AU - Manfreda, Alberto

AU - Marscher, Alan P.

AU - Marshall, Herman L.

AU - Massaro, Francesco

AU - Mitsuishi, Ikuyuki

AU - Ng, Chi-Yung

AU - O'Dell, Stephen L.

AU - Oppedisano, Chiara

AU - Papitto, Alessandro

AU - Pavlov, George G.

AU - Peirson, Abel L.

AU - Perri, Matteo

AU - Pesce-Rollins, Melissa

AU - Pilia, Maura

AU - Possenti, Andrea

AU - Puccetti, Simonetta

AU - Ramsey, Brian D.

AU - Roberts, Oliver J.

AU - Romani, Roger W.

AU - Sgrò, Carmelo

AU - Slane, Patrick

AU - Spandre, Gloria

AU - Swartz, Douglas A.

AU - Tamagawa, Toru

AU - Tavecchio, Fabrizio

AU - Taverna, Roberto

AU - Tawara, Yuzuru

AU - Thomas, Nicholas E.

AU - Trois, Alessio

AU - Tsygankov, Sergey S.

AU - Turolla, Roberto

AU - Vink, Jacco

AU - Wu, Kinwah

AU - Xie, Fei

PY - 2024/7/1

Y1 - 2024/7/1

N2 - We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer's (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = ‑25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1's au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1's spin is likely high (a * ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE's bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole.

AB - We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer's (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = ‑25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1's au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1's spin is likely high (a * ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE's bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole.

KW - Accretion

KW - Polarimetry

KW - X-ray astronomy

KW - Stellar mass black holes

KW - 14

KW - 1278

KW - 1810

KW - 1611

KW - Astrophysics - High Energy Astrophysical Phenomena

UR - https://www.mendeley.com/catalogue/b3a9b8c2-e50b-31e1-8d5c-e2ae13023068/

U2 - 10.3847/2041-8213/ad58e4

DO - 10.3847/2041-8213/ad58e4

M3 - Article

VL - 969

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - L30

ER -