Timing and Spectral properties of Be/X-ray pulsar EXO 2030+375 during a Type I outburst

TL;DR

This study analyzes the timing and spectral properties of the Be/X-ray pulsar EXO 2030+375 during a Type I outburst, revealing energy-dependent pulse profiles, spectral features, and absorption characteristics.

Contribution

It provides the first detailed broadband timing and spectral analysis of EXO 2030+375 during a Type I outburst, including pulse-phase-resolved spectroscopy and absorption modeling.

Findings

Detection of pulsations up to ~100 keV with energy-dependent profiles.

Presence of high-energy dips in pulse profiles up to ~70 keV.

Spectral analysis shows no cyclotron features and suggests variable absorption during dips.

Abstract

We present results from a study of broadband timing and spectral properties of EXO 2030+375 using a Suzaku observation. Pulsations with a period of 41.41 s and strong energy dependent pulse profiles were clearly detected up to ~100 keV. Narrow dips are seen in the profiles up to ~70 keV. Presence of prominent dips at several phases in the profiles up to such high energy ranges were not seen before. At higher energies, these dips gradually disappeared and the profile appeared single-peaked. The 1.0-200.0 keV broad-band spectrum is found to be well described by a partial covering high energy cut-off power-law model. Several low energy emission lines are also detected in the pulsar spectrum. We fitted the spectrum using neutral as well as partially ionized absorbers along with above continuum model yielding similar parameter values. The partial covering with partially ionized absorber resulted into marginally better fit. The spectral fitting did not require any cyclotron feature in the best fit model. To investigate the changes in spectral parameters at dips, we carried out pulse-phase-resolved spectroscopy. During the dips, the value of additional column density was estimated to be high compared to other pulse phases. While using partially ionized absorber, the value of ionization parameter is also higher at the dips. This may be the reason for the presence of dips up to higher energies. No other spectral parameters show any systematic variation with pulse phases of the pulsar.