Broad-band X-ray spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498$-$2921 during the 2023 outburst
Zhaosheng Li, L. Kuiper, Y. Y. Pan, M. Falanga, J. Poutanen, Y. P. Chen, R. X. Xu, M. Y. Ge, Y. Huang, L. M. Song, S. Zhang, F. J. Lu, S. N. Zhang
arXiv:2408.12786v1 Announce Type: new
Abstract: We report on the broadband spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498$-$2921 during its April 2023 outburst using data from NICER (1$-$10 keV), NuSTAR (3$-$79 keV), Insight-HXMT (2$-$150 keV), and INTEGRAL (30$-$150 keV). We detect significant 401 Hz pulsations across the 0.5$-$150 keV band. The pulse fraction increases from $sim$2% at 1 keV to $sim$13% at 66 keV. Five type-I X-ray bursts have been detected, including three photospheric radius expansion bursts, with a rise time of $sim$2 s and an exponential decay time of $sim$5 s. The recurrence time is $sim$9.1 h, which can be explained by unstable thermonuclear burning of hydrogen-deficient material on the neutron star surface. The quasi-simultaneous 1$-$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 $Gamma$ of $sim$1.8 and an electron temperature $kT_{rm e}$ of $sim$40 keV. We obtain a low inclination angle $isim34^{circ}$. The accretion disk shows properties of strong ionization, $log(xi/{rm erg~cm~s^{-1}})sim4.5$, over-solar abundance, $A_{rm Fe}sim 7.7$, and high density, $log(n_{rm e}/{rm cm^{-3}})sim 19.5$. However, a lower disk density with normal abundance and ionization could also be possible. From the inner disk radius $R_{rm in}=1.67R_{rm ISCO}$ and the long-term spin-down rate of $-3.1(2)times10^{-15}~{rm Hz~s^{-1}}$, we constrain the magnetic field of IGR J17498$-$2921 in the range of $(0.9-2.4)times10^8$ G.arXiv:2408.12786v1 Announce Type: new
Abstract: 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 $sim$2% at 1 keV to $sim$13% at 66 keV. Five type-I X-ray bursts have been detected, including three photospheric radius expansion bursts, with a rise time of $sim$2 s and an exponential decay time of $sim$5 s. The recurrence time is $sim$9.1 h, which can be explained by unstable thermonuclear burning of hydrogen-deficient material on the neutron star surface. The quasi-simultaneous 1$-$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 $Gamma$ of $sim$1.8 and an electron temperature $kT_{rm e}$ of $sim$40 keV. We obtain a low inclination angle $isim34^{circ}$. The accretion disk shows properties of strong ionization, $log(xi/{rm erg~cm~s^{-1}})sim4.5$, over-solar abundance, $A_{rm Fe}sim 7.7$, and high density, $log(n_{rm e}/{rm cm^{-3}})sim 19.5$. However, a lower disk density with normal abundance and ionization could also be possible. From the inner disk radius $R_{rm in}=1.67R_{rm ISCO}$ and the long-term spin-down rate of $-3.1(2)times10^{-15}~{rm Hz~s^{-1}}$, we constrain the magnetic field of IGR J17498$-$2921 in the range of $(0.9-2.4)times10^8$ G.