The reawakening of the sleeping X-ray pulsar XTE J1946+274

TL;DR

This paper studies the 2010/2011 outbursts of the X-ray pulsar XTE J1946+274, revealing variable cyclotron features and spectral properties, and discusses mechanisms behind its unusual outburst behavior.

Contribution

It presents new observational evidence of cyclotron line variability and spectral features in XTE J1946+274, enhancing understanding of its accretion and magnetic field properties.

Findings

Possible cyclotron line at 25 keV with 93% confidence

Exclusion of previously observed 35 keV cyclotron line

Spectral features vary with flux and pulse phase

Abstract

We report on a series of outbursts of the high mass X-ray binary XTE J1946+274 in 2010/2011 as observed with INTEGRAL, RXTE, and Swift. We discuss possible mechanisms resulting in the extraordinary outburst behavior of this source. The X-ray spectra can be described by standard phenomenological models, enhanced by an absorption feature of unknown origin at about 10 keV and a narrow iron K alpha fluorescence line at 6.4 keV, which are variable in flux and pulse phase. We find possible evidence for the presence of a cyclotron resonance scattering feature at about 25 keV at the 93% level. The presence of a strong cyclotron line at 35 keV seen in data from the source's 1998 outburst and confirmed by a reanalysis of these data can be excluded. This result indicates that the cyclotron line feature in XTE J1946+274 is variable between individual outbursts.