Probing thermonuclear bursts and X-ray reflection features in Aql X-1 during 2024 outburst

We report the broadband timing and spectral properties of the neutron star low-mass X-ray binary Aql X-1 during the 2024 outburst with NICER, NuSTAR, and Swift observatories. We detected six thermonuclear X-ray bursts during the NICER and NuSTAR observations, with the observed X-ray burst profiles exhibiting a strong energy dependence. The time-resolved burst spectra indicate the presence of soft excess during the burst, which can be modeled by using a variable persistent emission method ( f_a method) or the relxillNS reflection model. We found that the reflection model can contribute ∼20% of total emission as observed during the NICER burst. The reflection and blackbody component fluxes are strongly correlated, as observed during a burst. The excess emission is possible due to the enhanced mass accretion rate to the neutron star due to the Poynting-Rodertson drag, and a fraction of burst emission may be reflected from the disk. The bursts did not show photospheric radius expansion during the peak. Moreover, we examined the burst-free accretion emission in the broadband range with NuSTAR, NICER, and Swift at two epochs of the outburst. The persistent emission showed X-ray reflection features, which can be well modeled with the relativistic reflection model relxillCp. The inner disk radius (R_in) is found to be nearly 22 and 10 times R_g for two observations, respectively. Assuming that the inner disk is truncated at the magnetospheric radius, the magnetic field strength at the poles of the neutron star is estimated to be(0.6-1.9)x 10⁹ G.