Detection of Low-Frequency QPO From X-ray Pulsar XTE J1858+034 During Outburst in 2019 with NuSTAR

TL;DR

This paper reports the detection of a low-frequency QPO at 196 mHz from the X-ray pulsar XTE J1858+034 during its 2019 outburst, using NuSTAR and Swift data, and discusses its energy dependence and theoretical models.

Contribution

It presents the first detection and analysis of a low-frequency QPO in XTE J1858+034 during an outburst, with insights into its origin and energy behavior.

Findings

Detected a 196 mHz QPO with 6% RMS variability.

QPO strength is higher at high energies.

Both beat frequency and Keplerian models can explain the QPO.

Abstract

We study the timing properties of XTE J1858+034 using the Nuclear Spectroscopic Telescope Array (NuSTAR) and Burst Alert Telescope onboard Swift during the outburst in October--November 2019. We have investigated for Quasi-Periodic Oscillation (QPO) during the outburst and detected a low-frequency QPO at $\sim$196 mHz with $\sim$6% RMS variability from the NuSTAR observation. The QPO is fitted and explained with the model - power law and a Lorentzian component. We have also studied the variation of QPO frequency with energy. The beat frequency model and Keplerian frequency model both are suitable to explain the origin of the QPOs for the source. Regular pulsations and QPOs are found to be stronger in high energy which suits the beat frequency model. The variation of the hardness ratio is studied over the outburst which does not show any significant variation.