Relativistic X-ray reflection from the accreting millisecond X-ray pulsar IGR~J17498-2921

The accreting millisecond X-ray pulsar IGR~J17498-2921 went into X-ray outburst on April 13-15, 2023, for the first time since its discovery on August 11, 2011. Here, we report on the first follow-up {} observation of the source, performed on April 23, 2023, around ten days after the peak of the outburst. The {} spectrum of the persistent emission ($3-60$ {} band) is well described by an absorbed blackbody with a temperature of kTbb=1.61± 0.04{}, most likely arising from the NS surface and a Comptonization component with power-law index Γ=1.79±0.02, arising from a hot corona at kTₑ=16± 2 keV. The X-ray spectrum of the source shows robust reflection features which have not been observed before. We use a couple of self-consistent reflection models, { relxill} and { relxillCp}, to fit the reflection features. We find an upper limit to the inner disc radius of 6\: RISCO and 9\: RISCO from { relxill} and { relxillCp} model, respectively. The inclination of the system is estimated to be 40 from both reflection models. Assuming magnetic truncation of the accretion disc, the upper limit of magnetic field strength at the pole of the NS is found to be B 1.8× 10⁸ G. Furthermore, the {} observation revealed two type I X-ray bursts and the burst spectroscopy confirms the thermonuclear nature of the burst. The blackbody temperature reaches nearly $2.2$ keV at the peak of the burst.