Broadband X-ray spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498−2921 during the 2023 outburst
: Li, Z. S.; Kuiper, L.; Pan, Y. Y.; Falanga, M.; Poutanen, J.; Chen, Y. P.; Xu, R. X.; Ge, M. Y.; Huang, Y.; Song, L. M.; Zhang, S.; Lu, F. J.; Zhang, S. N.
Publisher: EDP Sciences
: 2024
: Astronomy and Astrophysics
: Astronomy & Astrophysics
: A92
: 691
: 0004-6361
: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202451260
: http://dx.doi.org/10.1051/0004-6361/202451260
: https://research.utu.fi/converis/portal/detail/Publication/470916126
: https://arxiv.org/abs/2408.12786
We report on the broadband spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498‑2921 during its April 2023 outburst. We used data from NICER (1–10 keV), NuSTAR (3–79 keV), Insight-HXMT (2–150 keV), and INTEGRAL (30–150 keV). We detected significant 401 Hz pulsations across the 0.5–150 keV band. The pulse fraction increases from ∼2% at 1 keV to ∼13% at 66 keV. We detected five type-I X-ray bursts, including three photospheric radius expansion bursts, with a rise time of ∼2 s and an exponential decay time of ∼5 s. The recurrence time is ∼9.1 h, which can be explained by unstable thermonuclear burning of hydrogen-deficient material on the neutron star surface. The quasi-simultaneous 1–150 keV broadband spectra from NICER, NuSTAR and INTEGRAL can be aptly fitted by an absorbed reflection model, relxillCp, and a Gaussian line of instrumental origin. The Comptonized emission from the hot corona is characterized by a photon index Γ of ∼1.8 and an electron temperature kTe of ∼40 keV. We obtained a low inclination angle i ∼ 34°. The accretion disk shows properties of strong ionization, log(ξ/erg cm s‑1)∼4.5, over-solar abundance, AFe ∼ 7.7, and high density, log(ne/cm‑3)∼19.5. However, a lower disk density with normal abundance and ionization could also be possible. Based on the inner disk radius of Rin = 1.67RISCO and the long-term spin-down rate of ‑3.1(2)×10‑15 Hz s‑1, we were able to constrain the magnetic field of IGR J17498‑2921 to the range of (0.9 ‑ 2.4)×108 G.
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This work was supported by the Major Science and Technology Program of Xinjiang Uygur Autonomous Region (No. 2022A03013-3), the National Natural Science Foundation of China (12103042, 12273030, 12173103, U1938107), and Minobrnauki grant 075-15-2024-647 (JP). This research has made use of data obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), provided by NASA’s Goddard Space Flight Center, and also from the HXMT mission, a project funded by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS).