The very high X-ray polarization of accreting black hole IGR J17091−3624 in the hard state

ABSTRACT We report the first detection of the X-ray polarization of the transient black hole X-ray binary IGR J17091–3624 taken with the Imaging X-ray polarimetry Explorer (IXPE) in 2025 March, and present the results of an X-ray spectropolarimetric analysis. The polarization was measured in the 2–8 keV band with $5.2~\sigma$ statistical confidence. We report a polarization degree (PD) of $9.1\pm 1.6$ per cent and a polarization angle of $83^{\circ }\pm 5^{\circ }$ (errors are $1~\sigma$ confidence). There is a hint of a positive correlation of PD with energy that is not statistically significant. We report that the source is in the corona-dominated hard state, which is confirmed by a hard power-law-dominated spectrum with weak reflection features and the presence of a Type-C quasi-periodic oscillation at $\sim 0.2$ Hz. The orientation of the emitted radio jet is not known, and so we are unable to compare it with the direction of X-ray polarization, but we predict the two to be parallel if the geometry is similar to that in Cygnus X-1 and Swift J1727.8–1613, the two hard state black hole binaries previously observed by IXPE. In the Comptonization scenario, the high observed PD requires a very favourable geometry of the corona, a high inclination angle (supported by the presence of a dip in the light curve) and possibly a mildly relativistic outflow and/or scattering in an optically thick wind.

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Publication Details

Journal
Monthly Notices of the Royal Astronomical Society
Published
2025-05-27
DOI
https://doi.org/10.1093/mnras/staf859
Citations
9
Primary Topic
Astrophysical Phenomena and Observations
Type
article
Field-Weighted Citation Impact
10.39

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article

The very high X-ray polarization of accreting black hole IGR J17091−3624 in the hard state

F. Vincentelli, M. Shidatsu, Juri Poutanen, Michal Dovčiak et al.
9 citations
Monthly Notices of the Royal Astronomical Society
Astrophysical Phenomena and Observations
10.39
article

The very high X-ray polarization of accreting black hole IGR J17091−3624 in the hard state

F. Vincentelli, M. Shidatsu, Juri Poutanen, Michal Dovčiak, Oluwashina Adegoke, M. S. Ewing, Chuen Siang Kang, María Díaz Trigo, Javier A. García, Adam Ingram, Riley Connors, M. C. Baglio, Lorenzo Marra, Francesco Tombesi, Fiamma Capitanio, Maxime Parra, T D Russell, Elias Kammoun, Edward Nathan, Barbara De Marco, P. Gandhi, Guglielmo Mastroserio, Vladislav Loktev, James F. Steiner, Alexandra Veledina, S. Bianchi, Maitrayee Gupta, Giorgio Matt, Pierre-Olivier Petrucci
article en
9 citations

Abstract

ABSTRACT We report the first detection of the X-ray polarization of the transient black hole X-ray binary IGR J17091–3624 taken with the Imaging X-ray polarimetry Explorer (IXPE) in 2025 March, and present the results of an X-ray spectropolarimetric analysis. The polarization was measured in the 2–8 keV band with $5.2~\sigma$ statistical confidence. We report a polarization degree (PD) of $9.1\pm 1.6$ per cent and a polarization angle of $83^{\circ }\pm 5^{\circ }$ (errors are $1~\sigma$ confidence). There is a hint of a positive correlation of PD with energy that is not statistically significant. We report that the source is in the corona-dominated hard state, which is confirmed by a hard power-law-dominated spectrum with weak reflection features and the presence of a Type-C quasi-periodic oscillation at $\sim 0.2$ Hz. The orientation of the emitted radio jet is not known, and so we are unable to compare it with the direction of X-ray polarization, but we predict the two to be parallel if the geometry is similar to that in Cygnus X-1 and Swift J1727.8–1613, the two hard state black hole binaries previously observed by IXPE. In the Comptonization scenario, the high observed PD requires a very favourable geometry of the corona, a high inclination angle (supported by the presence of a dip in the light curve) and possibly a mildly relativistic outflow and/or scattering in an optically thick wind.

Monthly Notices of the Royal Astronomical SocietyVol. 541(2)
University of Rome Tor Vergata (IT), Roma Tre University (IT), California Institute of Technology (US), Centre National de la Recherche Scientifique (FR), Goddard Space Flight Center (US), European Southern Observatory (DE), University of Helsinki (FI), University of Turku (FI), University of Milan (IT), Helsinki Institute of Physics (FI), Astronomical Observatory of Rome (IT), Czech Academy of Sciences, Astronomical Institute (CZ), Brera Astronomical Observatory (IT), Institute for Space Astrophysics and Planetology (IT), Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano (IT), Istituto Nazionale di Fisica Nucleare, Roma Tor Vergata (IT), Center for Astrophysics Harvard & Smithsonian (US), Istituto di Astrofisica Spaziale e Fisica cosmica di Palermo (IT), Istituto Nazionale di Fisica Nucleare, Sezione di Roma I (IT), University of Southampton (GB), Ehime University (JP), Villanova University (US), Newcastle University (GB), KTH Royal Institute of Technology (SE), National Institute for Astrophysics (IT), Université Grenoble Alpes (FR), Universitat Politècnica de Catalunya (ES)
Royal Society, Grantová Agentura České Republiky, Generalitat de Catalunya, Centre National d’Etudes Spatiales, Agenzia Spaziale Italiana, NordForsk, Centre National de la Recherche Scientifique, College of Natural Resources and Sciences, Humboldt State University, Agència de Gestió d'Ajuts Universitaris i de Recerca
Openalex Percentile: Top 2%
Astrophysical Phenomena and Observations
10.39
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