The Accreting Pulsar XTE J1946+274: Further Indication for a Cyclotron Line from Suzaku?

Abstract

We present a timing and spectral analysis of the X-ray pulsar XTE J1946+274 observed with Suzaku towards the end of a weak outburst in 2010 October and compare it with previous results. XTE J1946+274 is an X-ray transient with a Be-type companion and a neutron star with a ∼15.8 s pulse period. For this analysis we used both XIS(0,1,3) and PIN data. From the latter we confirm the previously determined pulse period and create pulse profiles for several energy bands. Despite a difference in the 20-60 keV flux of more than about one order of magnitude, we observe a comparatively good match between the pulse profiles for Suzaku and RXTE/PCA, the latter obtained during a different, brighter outburst in 2010, for the 20-40 keV energy range (while small differences are present in the 10-20 keV range). The X-ray spectrum can be well described by a Fermi-Dirac cutoff power law model along with a narrow Fe Kα fluorescence line at 6.4 keV. The strength of the Fe line is consistent with the continuum vs. line flux correlation observed in different outbursts of the source. We also investigate the possible presence of a Cyclotron Resonance Scattering Feature (CRSF) at 35 keV, which was detected in data from a previous outburst in 1998, and find marginal evidence for it in the Suzaku data. From an earlier analysis of the brighter 2010 outburst, a possible CRSF residual at 25 keV was reported, which is not visible in the Suzaku data.