New measurements of the cyclotron line energy in Cen X-3

TL;DR

This study measures the cyclotron line energy in Cen X-3 using Suzaku and NuSTAR, finding consistent values over different luminosities and comparing with previous measurements to understand magnetic field properties.

Contribution

First simultaneous broadband measurements of the cyclotron line energy in Cen X-3 with Suzaku and NuSTAR, confirming its stability across luminosities.

Findings

Cyclotron line energies are approximately 30 keV in both observations.

No significant dependence of CRSF on source luminosity.

CRSF measurements are consistent with previous data, indicating a stable magnetic field.

Abstract

We report results from the analysis of data from two observations of the accreting binary X-ray pulsar Cen X-3 carried out with the broadband X-ray observatories Suzaku and NuSTAR. The pulse profile is dominated by a broad single peak and show some energy dependence with two additional weak pulse peaks at energies below 15 and 25 keV respectively. The broadband X-ray spectrum for 0.8-60.0 keV for Suzaku and 3.0-60.0 keV for NuSTAR is fitted well with high energy cut-off power-law model along with soft-excess, multiple iron emission lines and a cyclotron absorption. The cyclotron line energy is found to be $30.29^{+0.68}_{-0.61}$ keV and $29.22^{+0.28}_{-0.27}$ keV respectively in the Suzaku and NuSTAR spectra. We make a comparison of these two measurements with four previous measurements of CRSF in Cen X-3 obtained with Ginga, BeppoSAX and RXTE. We find no evidence for a dependence of the CRSF on luminosity. Except for one CRSF measurement with BeppoSAX, the remaining measurements are consistent with a CRSF energy in the range of 29.5 - 30.0 keV over a luminosity range of 1.1-5.4 $\times 10^{37}$ ergs s$^{-1}$ different from several other sources that show considerable CRSF variation in the same luminosity range.