Understanding the spectral and timing behavior of a newly discovered transient X-ray pulsar Swift J0243.6+6124

TL;DR

This study analyzes the timing and spectral properties of the newly discovered X-ray pulsar Swift J0243.6+6124, revealing energy-dependent pulse profiles and spectral features, but no cyclotron line, using NuSTAR data.

Contribution

First detailed timing and spectral analysis of Swift J0243.6+6124, including pulse profile evolution and spectral modeling without cyclotron line detection.

Findings

Detected pulsations at ~9.85 s

Energy-dependent pulse profiles from broad to double-peaked

Spectral continuum well fitted with cutoff power-law plus blackbody

Abstract

We present the results obtained from timing and spectral studies of the newly discovered accreting X-ray binary pulsar Swift J0243.6+6124 using a NuSTAR observation in 2017 October at a flux level of ~280 mCrab. Pulsations at 9.85423(5) s were detected in the X-ray light curves of the pulsar. Pulse profiles of the pulsar were found to be strongly energy dependent. A broad profile at lower energies was found to evolve into a double peaked profile in $\ge$30keV. The 3-79 keV continuum spectrum of the pulsar was well described with a negative and positive exponential cutoff or high energy cutoff power law models modified with a hot blackbody at $\sim$3 keV. An iron emission line was also detected at 6.4 keV in the source spectrum. We did not find any signature of cyclotron absorption line in our study. Results obtained from phase-resolved and time-resolved spectroscopy are discussed in the paper.