The first X-ray polarimetric observation of the black hole binary LMC X-1

Creators: Podgorný, J.; Marra, L.; Muleri, F.; Rodriguez Cavero, N.; Ratheesh, A.; Dovčiak, M.; Mikušincová, R.; Brigitte, M.; Steiner, J. F.; Veledina, A.; Bianchi, S.; Krawczynski, H.; Svoboda, J.; Kaaret, P.; Matt, G.; Garcia, J. A.¹; Petrucci, P.-O.; Lutovinov, A.; Semena, A.; Di Marco, A.; Negro, M.; Weisskopf, M. C.; Ingram, A.; Poutanen, J.; Beheshtipour, B.; Chun, S.; Hu, K.; Mizuno, T.; Sixuan, Z.; Tombesi, F.; Zane, S.; Agudo, I.; Antonelli, L. A.; Bachetti, M.; Baldini, L.; Baumgartner, W. H.; Bellazzini, R.; Bongiorno, S. D.; Bonino, R.; Brez, A.; Bucciantini, N.; Capitanio, F.; Castellano, S.; Cavazzuti, E.; Chen, C.; Ciprini, S.; Costa, E.; De Rosa, A.; Del Monte, E.; Di Gesu, L.; Di Lalla, N.; Donnarumma, I.; Doroshenko, V.; Ehlert, S. R.; Enoto, T.; Evangelista, Y.; Fabiani, S.; Ferrazzoli, R.; Gunji, S.; Hayashida, K.; Heyl, J.; Iwakiri, W.; Jorstad, S. G.; Karas, V.; Kislat, F.; Kitaguchi, T.; Kolodziejczak, J. J.; La Monaca, F.; Latronico, L.; Liodakis, I.; Maldera, S.; Manfreda, A.; Marin, F.; Marinucci, A.; Marscher, A. P.; Marshall, H. L.; Massaro, F.; Mitsuishi, I.; Ng, C.-Y.; O'Dell, S. L.; Omodei, N.; Oppedisano, C.; Papitto, A.; Pavlov, G. G.; Peirson, A. L.; Perri, M.; Pesce-Rollins, M.; Pilia, M.; Possenti, A.; Puccetti, S.; Ramsey, B. D.; Rankin, J.; Roberts, O. J.; Romani, R. W.; Sgrò, C.; Slane, P.; Soffitta, P.; Spandre, G.; Swartz, D. A.; Tamagawa, T.; Tavecchio, F.; Taverna, R.; Tawara, Y.; Tennant, A. F.; Thomas, N. E.; Trois, A.; Tsygankov, S. S.; Turolla, R.; Vink, J.; Wu, K.; Xie, F.

1. California Institute of Technology

Abstract

We report on an X-ray polarimetric observation of the high-mass X-ray binary LMC X-1 in the high/soft state, obtained by the Imaging X-ray Polarimetry Explorer (IXPE) in 2022 October. The measured polarization is below the minimum detectable polarization of 1.1 per cent (at the 99 per cent confidence level). Simultaneously, the source was observed with the Neutron Star Interior Composition Explorer (NICER), Nuclear Spectroscopic Telescope Array (NuSTAR), and Spectrum-Rontgen-Gamma (SRG)/Astronomical Roentgen Telescope – X-ray Concentrator (ART-XC) instruments, which enabled spectral decomposition into a dominant thermal component and a Comptonized one. The low 2–8 keV polarization of the source did not allow for strong constraints on the black hole spin and inclination of the accretion disc. However, if the orbital inclination of about 36° is assumed, then the upper limit is consistent with predictions for pure thermal emission from geometrically thin and optically thick discs. Assuming the polarization degree of the Comptonization component to be 0, 4, or 10 per cent, and oriented perpendicular to the polarization of the disc emission (in turn assumed to be perpendicular to the large-scale ionization cone orientation detected in the optical band), an upper limit to the polarization of the disc emission of 1.0, 0.9, or 0.9 per cent, respectively, is found (at the 99 per cent confidence level).

Copyright and License

© The Author(s) 2023. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

The Imaging X-ray Polarimetry Explorer (IXPE) is a joint US and Italian mission. The US contribution is supported by the National Aeronautics and Space Administration (NASA) and led and managed by its Marshall Space Flight Center (MSFC), with industry partner Ball Aerospace (contract NNM15AA18C). The Italian contribution is supported by the Italian Space Agency (Agenzia Spaziale Italiana, ASI) through contract ASI-OHBI-2017-12-I.0, agreements ASI-INAF-2017-12-H0 and ASI-INFN-2017.13-H0, and its Space Science Data Center (SSDC) with agreements ASI-INAF-2022-14-HH.0 and ASI-INFN 2021-43-HH.0, and by the Istituto Nazionale di Astrofisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) in Italy. This research used data products provided by the IXPE Team (MSFC, SSDC, INAF, and INFN) and distributed with additional software tools by the High-Energy Astrophysics Science Archive Research Center (HEASARC), at NASA Goddard Space Flight Center (GSFC).

The authors thank the referee, Andrzej Zdziarski, for very detailed and useful comments. JPod, MD, JS, and VK thank for the support from the GACR project 21–06825X and the institutional support from RVO:67985815. AV acknowledges support from the Academy of Finland grants 347003 and 355672. HK and NRC acknowledge NASA support under grants 80NSSC18K0264, 80NSSC22K1291, 80NSSC21K1817, and NNX16AC42G. P-OP acknowledges financial support from the French High Energy Program (PNHE/CNRS) and from the French Space Agency (CNES). AI acknowledges support from the Royal Society.

Data Availability

The IXPE data used in this paper are publicly available in the HEASARC data base (https://heasarc.gsfc.nasa.gov/docs/ixpe/archive/). The analysis and simulation software IXPEOBSSIM developed by IXPE collaboration and its documentation is available publicly through the webpage https://ixpeobssim.readthedocs.io/en/latest/?badge = latest.494. The NICER and NuSTAR data underlying this paper are publicly available from the NuSTAR (https://heasarc.gsfc.nasa.gov/docs/nustar/archive/nustar_archive.html) and NICER (https://heasarc.gsfc.nasa.gov/docs/nicer/nicer_archive.html) archives. The ART-XC data used in this paper publicly available at ftp://hea.iki.rssi.ru/public/SRG/ART-XC/data/LMC_X-1/lmc_x_1_barycen.fits.gz. The XSPEC software is publicly available in the HEASARC data base (https://heasarc.gsfc.nasa.gov/xanadu/xspec/). The corresponding XSPEC packages used for this work can be found in the references stated in this paper or shared on reasonable request.

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