Spectral & Timing analysis of Be/X-ray binary EXO 2030+375 during its giant 2021 outburst

TL;DR

This paper presents a detailed spectral and timing analysis of the Be/X-ray binary EXO 2030+375 during its 2021 giant outburst, revealing evolving pulse profiles, spectral features, and physical insights into the system's behavior.

Contribution

It provides a comprehensive multi-instrument analysis of the source during a giant outburst, highlighting spectral features and pulse profile evolution not previously detailed.

Findings

Pulse profiles evolve with energy and time.

Iron emission line detected at 6-7 keV.

Absorption features observed during peak outburst.

Abstract

We report the X-ray spectral and timing analysis of the high mass X-ray binary EXO 2030+375 during the 2021 type II outburst. We have incorporated NuSTAR, NICER, \textit{Swift}/BAT \& \textit{Fermi}/GBM observations to carry out a comprehensive analysis of the source. Pulse profiles in different energy ranges and time intervals have been generated and analyzed. We have performed a brief comparison of the observations amidst the peak outburst condition and also during the decaying state of the outburst. Pulse profiles are found to evolve with time and energy. An iron emission line at (6-7) keV is observed in the X-ray continuum. Distinct absorption features were observed in the spectra corresponding to the peak outburst state while such features were not detected during the later decaying phase of the outburst. We have estimated the characteristic spin-up time scale to be $\backsim$ 60 years. The continuum flux of the system and the varying luminosities covering the entire outburst period have been used to interpret the characteristics of the source. We have summarized the variability of various parameters along with their underlying physical implications.