Pulse phase dependent variations of the cyclotron absorption features of the accreting pulsars A 0535+26, XTE J1946+274 and 4U 1907+09 with Suzaku

TL;DR

This study performs pulse phase resolved spectral analysis of cyclotron resonant scattering features in three accreting pulsars, revealing strong phase-dependent variations that inform about magnetic field geometry and accretion environment.

Contribution

It provides the first detailed phase-resolved analysis of CRSFs in these pulsars using Suzaku data, highlighting magnetic field deviations and local environmental effects.

Findings

CRSF parameters vary strongly with pulse phase

Variation patterns are consistent across different spectral models

Absorption features correlate with pulse profile dips

Abstract

We have performed a detailed pulse phase resolved spectral analysis of the cyclotron resonant scattering features (CRSF) of the two Be/X-ray pulsars A0535+26 and XTE J1946+274 and the wind accreting HMXB pulsar 4U 1907+09 using Suzaku observations. The CRSF parameters vary strongly over the pulse phase and can be used to map the magnetic field and a possible deviation form the dipole geometry in these sources. It also reflects the conditions at the accretion column and the local environment over the changing viewing angles. The pattern of variation with pulse phase are obtained with more than one continuum spectral models for each source, all of which give consistent results. Care is also taken to perform the analysis over a stretch of data having constant spectral characteristics and luminosity to ensure that the results reflect the variations due to the changing viewing angle alone. For A0535+26 and XTE J1946+274 which show energy dependent dips in their pulse profiles, a partial covering absorber is added in the continuum spectral models to take into account an additional absorption at those phases by the accretion stream/column blocking our line of sight.