A1 Refereed original research article in a scientific journal
Exploring MAXI J1744-294: IXPE Insights into a Galactic Center X-Ray Transient
Authors: Marra, Lorenzo; Mikusincova, Romana; Vincentelli, Federico M.; Capitanio, Fiamma; Del Santo, Melania; Fabiani, Sergio; Mandel, Shifra; Muleri, Fabio; Parra, Maxime; Soffitta, Paolo; Tarana, Antonella; Baglio, M. Cristina; Bianchi, Stefano; Corbel, Stephane; Costa, Enrico; D'Ai, Antonino; De Marco, Barbara; Dovciak, Michal; Gianolli, Vittoria Elvezia; Gnarini, Andrea; Gupta, Maitrayee; Ingram, Adam; Mastroserio, Guglielmo; Matt, Giorgio; Mori, Kaya; Petrucci, Pierre-Olivier; Podgorny, Jakub; Poutanen, Juri; Steiner, James F.; Svoboda, Jiri; Taverna, Roberto; Tombesi, Francesco; Ravi, Swati; Rodriguez, Jerome; Russell, Thomas D.; Veledina, Alexandra; Zhang, Shuo
Publication year: 2026
Journal: Astrophysical Journal
Article number: 178
Volume: 1001
Issue: 2
ISSN: 0004-637X
eISSN: 1538-4357
DOI: https://doi.org/10.3847/1538-4357/ae5488
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Open Access publication channel
Web address : https://iopscience.iop.org/article/10.3847/1538-4357/ae5488
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/523311623
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
We present the first IXPE spectro-polarimetric observation of the black hole candidate MAXI J1744−294, a transient X-ray source observed during a bright 2025 outburst in the Galactic center region. The source has recently been identified as most likely a repeat outburst of the 2016 transient Swift J174540.2−290037. During the ∼150 ks observation, the source was detected in the soft state, and its spectrum was well described by an absorbed multicolor disk with a minor high-energy tail. We did not detect any significant polarization from the source, and hence we derived a 3σ upper limit on the polarization degree of 1.3% in the 2–8 keV energy band. This result is consistent with previous findings for soft-state black hole binaries observed at low to intermediate inclination angles. By comparing the polarization degree upper limit with theoretical predictions for standard accretion disk emission, we constrain the disk inclination to i ≲ 38°–72°, depending on the black hole spin and the disk atmosphere albedo, consistent with inclination estimates obtained during the 2016 outburst of Swift J174540.2−290037.
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Funding information in the publication:
L.M., F.M., P.S., G.Matt, and R.T. acknowledge support from the project PRIN 2022–2022LWPEXW, “An X-Ray View of Compact Objects in Polarized Light,” European Union funding, Next Generation EU, Mission 4, Component 1, CUP C53D23001180006. F.M.V. is supported by the European Union’s Horizon Europe research and innovation program through the Marie Skłodowska-Curie grant agreement No. 101149685. F.C. and A.T. acknowledge financial support from the Istituto Nazionale di Astrofisica (INAF) grant No. 1.05.23.05.06, “Spin and Geometry in Accreting X-Ray Binaries: The First Multi-frequency Spectro-polarimetric Campaign.” M.D.S. and A.D. acknowledge ASI-INAF program I/004/11/6 (Swift) and funding from the European Union, Next Generation EU, Mission 4, Component 1, CUP C53D23001330006 (PRIN MUR 2022 SEAWIND project No. 2022Y2T94C). S.F. acknowledges financial support from the Istituto Nazionale di Astrofisica (INAF) grant No. 1.05.24.02.04: “A Multi-frequency Spectro-polarimetric Campaign to Explore Spin and Geometry in Low Mass X-Ray Binaries.” M.D., M.G., J.Pod., and J.S. thank GACR project 21-06825X for the support and institutional support from RVO:67985815. V.E.G. acknowledges funding under NASA contract 80NSSC24K1403. A.I. acknowledges support from the Royal Society. P.O.P. acknowledges financial support from the CNRS, “Action Thématique Processus Extrêmes et Multimessagers,” and from the CNES, the French Space Agency. A.V. acknowledges support from the Academy of Finland grant No. 355672. Nordita is supported in part by NordForsk. A.G. was supported by an appointment to the NASA Postdoctoral Program at the Marshall Space Flight Center (MSFC), administered by Oak Ridge Associated Universities under contract with NASA.
