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Discovery of polarized X-ray emission from the accreting millisecond pulsar SRGA J144459.2–604207
Tekijät: Papitto, Alessandro; Di Marco, Alessandro; Poutanen, Juri; Salmi, Tuomo; Illiano, Giulia; La Monaca, Fabio; Ambrosino, Filippo; Bobrikova, Anna; Cristina Baglio, Maria; Ballocco, Caterina; Burderi, Luciano; Campana, Sergio; Coti Zelati, Francesco; Di Salvo, Tiziana; La Placa, Riccardo; Loktev, Vladislav; Long, Sinan; Malacaria, Christian; Miraval Zanon, Arianna; Ng, Mason; Pilia, Maura; Sanna, Andrea; Stella, Luigi; Strohmayer, Tod; Zane, Silvia
Kustantaja: EDP Sciences
Kustannuspaikka: LES ULIS CEDEX A
Julkaisuvuosi: 2025
Journal: Astronomy and Astrophysics
Tietokannassa oleva lehden nimi: Astronomy & Astrophysics
Lehden akronyymi: ASTRON ASTROPHYS
Artikkelin numero: A37
Vuosikerta: 694
Sivujen määrä: 9
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202451775
Verkko-osoite: https://doi.org/10.1051/0004-6361/202451775
Rinnakkaistallenteen osoite: https://research.utu.fi/converis/portal/detail/Publication/485101248
We report the discovery of polarized X-ray emission from an accreting millisecond pulsar. During a 10-day-long coverage of the February 2024 outburst of SRGA J144459.2-604207, the Imaging X-ray Polarimetry Explorer (IXPE) detected an average polarization degree of the 2-8 keV emission of 2.3%+/- 0.4% at an angle of 59 degrees +/- 6 degrees (east of north; the uncertainties quoted are at the 1 sigma confidence level). The polarized signal shows a significant energy dependence with a degree of 4.0%+/- 0.5% between 3 and 6 keV and < 1.5% (90% c.l.) in the 2-3 keV range. We used NICER, XMM-Newton, and NuSTAR observations to obtain an accurate pulse-timing solution and to perform a phase-resolved polarimetric analysis of IXPE data. We did not detect any significant variability in the Stokes parameters Q and U with the spin and orbital phases. We used the relativistic rotating-vector model to show that a moderately fan-beam emission from two point-like spots at low magnetic obliquity (similar or equal to 10 degrees) is compatible with the observed pulse profile and polarization properties. IXPE also detected 52 type I X-ray bursts whose recurrence time Delta t(rec) increased from 2 to 8 h as a function of the observed count rate C as Delta t(rec) proportional to C-0.8. We stacked the emission observed during all the bursts and obtained an upper limit on the polarization degree of 8.5% (90% c.l.).
Ladattava julkaisu This is an electronic reprint of the original article. |  |
Julkaisussa olevat rahoitustiedot:
We warmly thank the Directors and the Science Operations Team of IXPE, NICER, NuSTAR, and XMM for promptly scheduling the observations reported here and Bas Dorsman, Matteo Bachetti and Anna Watts for useful discussions. 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-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. 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). NICER is a 0.2–12 keV X-ray telescope operating on the International Space Station, funded by NASA. The NuSTAR mission is a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. Data analysis was performed using the NuSTAR Data Analysis Software (NuSTARDAS), jointly developed by the ASI Science Data Center (SSDC, Italy) and the California Institute of Technology (USA). XMM-Newton is an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. MN and this work were supported by NASA under grant 80NSSC24K1175. AP, GI, FA, RLP, CM and LS are supported by INAF Research Grant FANS and the Italian Ministry of University and Research PRIN 2020 Grant 2020BRP57Z (GEMS). AP acknowledges support from the Fondazione Cariplo/CDP, grant no. 2023-2560. JP thanks the Ministry of Science and Higher Education grant 075-15-2024-647 for support. AB acknowledges support from the Finnish Cultural Foundation grant 00240328. MCB acknowledges support from the INAF-Astrofit fellowship. FCZ is supported by a Ramón y Cajal fellowship (grant agreement RYC2021-030888-I). TS acknowledges support from ERC Consolidator Grant No. 865768 AEONS (PI: Watts).
