Comprehensive analysis of the transient X-ray pulsar MAXI J1409 619

Abstract

We probe the properties of the transient X-ray pulsar MAXI J1409-619 through RXTE and Swift follow-up observations of the outburst in 2010. We are able to phase-connect the pulse arrival times for the 25 d episode during the outburst. We suggest that either an orbital model (with P-orb similar or equal to 14.7(4) d) or a noise process due to random torque fluctuations (with S-r approximate to 1.3 x 10(-18) Hz(2) S-2 Hz(-1)) is plausible to describe the residuals of the timing solution. The frequency derivatives indicate a positive torque-luminosity correlation, which implies temporary accretion disc formation during the outburst. We also discover several quasiperiodic oscillations in company with their harmonics whose centroid frequencies decrease as the source flux decays. The variation of the pulsed fraction and spectral power-law index of the source with X-ray flux is interpreted as the sign of transition from a critical to a subcritical accretion regime at the critical luminosity within the range of 6 x 10(37)-1.2 x 10(38) erg s(-1). Using pulse-phase-resolved spectroscopy, we show that the phases with higher flux tend to have lower photon indices, indicating that the polar regions produce spectrally harder emission.