Spectral and type I X-ray burst studies of 4U 1702−429 using AstroSat observations

Abstract

4U 1702−429, an atoll-type neutron star low-mass X-ray binary, was observed twice by AstroSat/Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counters (LAXPC-20) on 2018 April 27 and 2019 August 8. Persistent emission spectra of the source were well fitted with model combination - $\mathtt {constant \times tbabs (thcomp \times diskbb+powerlaw)}$. The parameters obtained from spectral analysis revealed the source to be in hard spectral state during the observations. Time-resolved spectral analyses were performed on the three type I X-ray bursts detected from the source. Burst analysis showed that the source underwent a photospheric radius expansion. Consequently, radius of the neutron star and distance to the source (with isotropic and anisotropic burst emission) were obtained to be 12.65 $^{+0.90}_{-0.86}$ km, and 6.92 $^{+0.16}_{-0.09}$ and 8.43 $^{+0.20}_{-0.10}$ kpc, respectively.