A1 Refereed original research article in a scientific journal
Polarization of reflected X-ray emission from the Sgr A molecular complex: Multiple flares, multiple sources?
Authors: Khabibullin, Ildar; Churazov, Eugene; Ferrazzoli, Riccardo; Kaaret, Philip; Kolodziejczak, Jeffery J.; Marin, Frédéric; Sunyaev, Rashid; Svoboda, Jiri; Vikhlinin, Alexey; Barnouin, Thibault; Chen, Chien-Ting; Costa, Enrico; Di Gesu, Laura; Di Marco, Alessandro; Ehlert, Steven R.; Forman, William; Kim, Dawoon E.; Kraft, Ralph; Peter, Maksym W.; Matt, Giorgio; Poutanen, Juri; Soffitta, Paolo; Swartz, Douglas A.; Agudo, Ivan; Angelo Antonelli, Lucio; Baldini, Luca; Baumgartner, Wayne H.; Bellazzini, Ronaldo; Bianchi, Stefano; Bongiorno, Stephen D.; Bonino, Raffaella; Brez, Alessandro; Bucciantini, Niccolo; Capitanio, Fiamma; Castellano, Simone; Cavazzuti, Elisabetta; Ciprini, Stefano; De Rosa, Alessandra; Del Monte, Ettore; Di Lalla, Niccolò; Donnarumma, Immacolata; Doroshenko, Victor; Dovciak, Michal; Enoto, Teruaki; Evangelista, Yuri; Fabiani, Sergio; Garcia, Javier A.; Gunji, Shuichi; Hayashida, Kiyoshi; Heyl, Jeremy; Iwakiri, Wataru; Jorstad, Svetlana G.; Karas, Vladimir; Kislat, Fabian; Kitaguchi, Takao; Krawczynski, Henric; La Monaca, Fabio; Latronico, Luca; Liodakis, Ioannis; Maldera, Simone; Manfreda, Alberto; Marscher, Alan P.; Marshall, Herman L.; Massaro, Francesco; Mitsuishi, Ikuyuki; Mizuno, Tsunefumi; Muleri, Fabio; Negro, Michela; Ng,, Chi-Yung; O’Dell, Stephen L.; Omodei, Nicola; Oppedisano, Chiara; Papitto, Alessandro; Pavlov, George G.; Peirson, Abel Lawrence; Pesce-Rollins, Melissa; Petrucci, Pierre-Olivier; Pilia, Maura; Possenti, Andrea; Puccetti, Simonetta; Ramsey, Brian D.; Rankin, John; Ratheesh, Ajay; Roberts, Oliver J.; Romani, Roger W.; Sgro, Carmelo; Slane, Patrick; Spandre, Gloria; Tamagawa, Toru; Tavecchio, Fabrizio; Taverna, Roberto; Tawara, Yuzuru; Tennant, Allyn F.; Thomas, Nicholas E.; Tombesi, Francesco; Trois, Alessio; Tsygankov, Sergey S.; Turolla, Roberto; Vink, Jacco; Weisskopf, Martin C.; Wu, Kinwah; Xie, Fei; Zane, Silvia
Publisher: EDP Sciences
Publication year: 2026
Journal: Astronomy and Astrophysics
Article number: A270
Volume: 707
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202556768
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Open Access publication channel
Web address : https://doi.org/10.1051/0004-6361/202556768
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/523439174
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
The extended X-ray emission observed in the direction of several molecular clouds in the central molecular zone (CMZ) of our Galaxy exhibits spectral and temporal properties consistent with the X-ray echo scenario. This concept postulates that the observed signal is a light-travel-time delayed reflection of a short (δt <1.5 yr) and bright (LX > 1039 erg s−1) flare that was most probably produced a few hundred years ago by Sgr A*. This scenario also predicts a distinct polarization signature for the reflected X-ray continuum, with the polarization vector being perpendicular to the direction toward the primary source and the polarization degree being determined by the scattering angle. We report the results of two deep observations of the currently brightest (in reflected emission) molecular complex Sgr A taken with the Imaging X-ray Polarimetry Explorer (IXPE) in 2022 and 2023. We confirm the previous polarization measurement for a large region encompassing the Sgr A complex with high significance. We also reveal an inconsistent polarization pattern for the brightest reflection region in its center. Specifically, the X-ray polarization from this region is almost perpendicular to the expected direction in the case of Sgr A* illumination, and it shows a smaller degree of polarization compared to the large region. Taken at face value, this could indicate the simultaneous propagation of several illumination fronts throughout the CMZ, with the origin of one of them not being Sgr A*. The primary source could be associated with the Arches stellar cluster or a currently unknown source located closer to the illuminated cloud, potentially lowering the required luminosity of the primary source. Although significantly deeper observations with IXPE would be required to unequivocally distinguish between the scenarios, a combination of high-resolution imaging and micro-calorimetric spectroscopy offers an additional promising path forward.
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Funding information in the publication:
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-2022-13-I.0, agreements ASI-INAF-2022-19-HH.0 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. IK acknowledges support by the COMPLEX project from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program grant agreement ERC-2019-AdG 882679. JS thanks GACR project 21-06825X. AV, RK, and WF acknowledge support from the Smithsonian Institution and the Chandra High Resolution Camera Project through NASA contract NAS8-03060. IL was funded by the European Union ERC-2022-STG – BOOTES – 101076343. RF, ECo, ADM, PSo, FLM, FMu, and SF are partially supported by MAECI with grant CN24GR08 “GRBAXP: Guangxi-Rome Bilateral Agreement for X-ray Polarimetry in Astrophysics”.
