Spectro-temporal and type I X-ray burst analysis of GX 3+1 using AstroSat observations

Abstract

ABSTRACT GX 3+1, an atoll type neutron star low-mass X-ray binary, was observed four times by Soft X-ray Telescope and The Large Area X-ray Proportional Counter on-board AstroSat between 2017 October 5 and 2018 August 9. The hardness-intensity-diagram of the source showed it to be in the soft spectral state during all the four observations. The spectra of the source could be adequately fit with a model consisting of blackbody ($\tt {bbody}$) and power--law ($\tt {powerlaw}$) components. This yielded the blackbody radius and mass accretion rate to be ∼8 km and ∼2 × 10−9 M⊙ y−1, respectively. In one of the observations, a type I X-ray burst having a rise and e-folding time of 0.6 and 5.6 s, respectively, was detected. Time-resolved spectral analysis of the burst showed that the source underwent a photospheric radius expansion. The radius of the emitting blackbody in GX 3+1 and its distance were estimated to be 9.19 $\substack{+0.97\\ -0.82}$ km and 10.17 $\substack{+0.07\\ -0.18}$ kpc, respectively. Temporal analysis of the burst yielded upper limits of the fractional root mean square amplitude of 7${{\ \rm per\ cent}}$, 5${{\ \rm per\ cent}}$, and 6${{\ \rm per\ cent}}$ during burst start, burst maximum, and right after the radius expansion phase, respectively.