Broad-band X-ray spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498-2921 during the 2023 outburst

We report on the broadband spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498-2921 during its April 2023 outburst using data from NICER (1-10 keV), NuSTAR (3-79 keV), Insight-HXMT (2-150 keV), and INTEGRAL (30-150 keV). We detect 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. Five type-I X-ray bursts have been detected, 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 well 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 of 1. 8 and an electron temperature kT ₄ of 40 keV. We obtain a low inclination angle i34^. The accretion disk shows properties of strong ionization, (/ erg~cm~s^{-1}) 4. 5, over-solar abundance, A ₅₄ 7. 7, and high density, (n ₄/ cm^{-3}) 19. 5. However, a lower disk density with normal abundance and ionization could also be possible. From the inner disk radius R ₈₍=1. 67R ₈ₒ₂₎ and the long-term spin-down rate of -3. 1 (2) 10^-15~ Hz~s^{-1}, we constrain the magnetic field of IGR J17498-2921 in the range of (0. 9-2. 4) 10⁸ G.