NuSTAR and AstroSat observations of GX 9+1: spectral and temporal studies

Abstract

We have studied the spectro-temporal properties of the neutron star low mass X-ray binary GX 9+1 using data from NuSTAR/FPM and AstroSat/SXT and LAXPC. The hardness-intensity diagram of the source showed it to be in the soft spectral state during both observations. NuSTAR spectral analysis yielded an inclination angle (θ) = 29${^{+3}_{-4}}^{\circ }$ and inner disk radius (Rin) ≤ 19.01 km. Assuming that the accretion disk was truncated at the Alfvén radius during the observation, the upper limit of the magnetic dipole moment (μ) and the magnetic field strength (B) at the poles of the neutron star in GX 9+1 were calculated to be 1.45×1026 G cm3 and 2.08×108 G, respectively (for kA = 1). Flux resolved spectral analysis with AstroSat data showed the source to be in the soft spectral state (Fdisk/Ftotal ∼0.9) with a monotonic increase in mass accretion rate ($\dot{m}$) along the banana branch. The analysis also showed the presence of absorption edges at ∼1.9 and ∼2.4 keV, likely due to Si XIII and S XV, respectively. Temporal analysis with LAXPC-20 data in the 0.02 − 100 Hz range revealed the presence of noise components, which could be characterized with broad Lorentzian components.