Giant outburst of EXO 2030+375: pulse-phase resolved analysis of INTEGRAL data

TL;DR

This study analyzes the pulse-phase resolved X-ray spectra of the Be/X-ray binary EXO 2030+375 during a giant outburst, revealing spectral variability, emission geometry changes, and potential cyclotron features.

Contribution

First pulse-phase resolved spectral analysis of EXO 2030+375 during a giant outburst using INTEGRAL data, showing emission geometry evolution and cyclotron line evidence.

Findings

Spectral variability with pulse phase observed.

Emission geometry shifts from fan-beam to combined pencil and fan-beam.

Possible cyclotron absorption line detected at 63 keV.

Abstract

In June-September 2006 the Be/X-ray binary EXO 2030+375 experienced the second giant outburst since its discovery. The source was shown to have a complicated pulse-averaged X-ray spectral continuum with possible evidence of cyclotron absorption features. In this paper we present the first pulse-phase resolved analysis of the broad band X-ray spectra of EXO 2030+375 obtained with the INTEGRAL observatory close to the maximum and during the decay phase of the giant outburst. We report a strong variability of the spectrum with pulse phase. Alternative spectral continuum models are discussed. The dependence of the spectral parameters on pulse phase during the maximum of the outburst and the evolution of the pulse profiles with time are qualitatively consistent with the pulsar's emission diagram changing from the fan-beam geometry close to the maximum of the outburst to a combination of pencil and fan beams (of comparable intesities) at the end of the decay phase. Evidence of a cyclotron absorption line around 63 keV at the pulse phase interval preceeding the main peak of the pulse profile is present in the spectrum obtained close to the maximum of the outburst.