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

¹ Dr. Karl Remeis-Observatory & ECAP, Universität Erlangen Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
e-mail: Sebastian.Mueller@sternwarte.uni-erlangen.de
² CEA Saclay, DSM/IRFU/SAp-UMR AIM (7158) CNRS/CEA/Université Paris 7, Diderot, 91191 Gif-sur-Yvette, France
³ CRESST and NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA and Center for Space Science and Technology, UMBC, Baltimore, MD 21250, USA
⁴ Department of Physics, Florida International University, Miami, FL 33199, USA
⁵ ISDC Data Center for Astrophysics, University of Geneva, 16 chemin d’Écogia, 1290 Versoix, Switzerland
⁶ Center for Astronomy and Space Sciences, University of California, San Diego, La Jolla, CA 92093, USA
⁷ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany

Received: 11 May 2012
Accepted: 29 August 2012

Abstract

We report on a series of outbursts of the high-mass X-ray binary XTE J1946+274 in 2010/2011 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 Kα fluorescence line at 6.4 keV, which are variable in flux and pulse phase. We find possible evidence for 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 that was 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.