RXTE and SWIFT Observations of SWIFT J1729.9-3437

TL;DR

This study analyzes RXTE and Swift observations of SWIFT J1729.9-3437, revealing its spin behavior, orbital parameters, pulse profile changes, spectral features, and phase-dependent spectral variations during its 2010 outburst.

Contribution

It provides detailed timing and spectral analysis of SWIFT J1729.9-3437, including spin, orbital, and pulse profile characteristics, with insights into spectral features and phase-dependent properties.

Findings

Spin frequency and derivative measured precisely.

Orbital period estimated at 15.3 days with a possible torque noise explanation.

Pulse profile switches from double to single peak as flux decreases.

Abstract

We analyze \emph{RXTE} and \emph{Swift} observations of SWIFT J1729.9$-$3437 after its outburst from 2010 July 20 to 2010 August 12. We calculate a spin frequency and spin frequency derivative of $1.8734(8) \times 10^{-3}$ Hz and $6.42(6) \times 10^{-12}$ Hz/s respectively from the quadratic fit of pulse arrival times. The quadratic fit residuals fit well to a circular orbital model with a period of $15.3(2)$ days and a mass function of about $1.3M_{\odot}$, but they can also be explained by a torque noise strength of $6.8 \times 10^{-18}$ Hz sec$^{-2}$. Pulse profiles switches from double-peaked to single-peaked as the source flux continues to decrease. We find that the pulse shape generally shows no strong energy dependence. The hardness ratios reveal that the source becomes softer with decreasing flux. We construct a single spectrum from all the available RXTE and Swift observations. We find that adding an \emph{Fe} line complex feature around 6.51 keV slightly improves the spectral fit and that this feature is more likely to originate from the source rather than the Galactic ridge. From the pulse phase spectral analysis, it is shown that that photon index and folding energy of the high energy cut-off vary with varying pulse phase.