BeppoSAX observations of XTE J1946+274

Abstract

We report on the BeppoSAX monitoring of a giant outburst of the transient X-ray pulsar XTE J1946+274 in 1998. The source was detected with a flux of ~ 4 x 10^(-9) erg cm^(-2) s^(-1) (in 0.1 - 120 keV range). The broadband spectrum, typical for accreting pulsars, is well described by a cutoff power law with a cyclotron resonance scattering feature (CRSF) at ~ 38 keV. This value is consistent with earlier reports based on the observations with Suzaku at factor of ten lower luminosity, which implies that the feature is formed close to the neutron star surface rather than in the accretion column. Pulsations with P ~ 15.82 s were observed up to ~ 70 keV. The pulse profile strongly depends on energy and is characterised by a "soft" and a "hard" peaks shifted by half period, which suggests a strong phase dependence of the spectrum, and that two components with roughly orthogonal beam patterns are responsible for the observed pulse shape. This conclusion is supported by the fact that the CRSF, despite its relatively high energy, is only detected in the spectrum of the soft peak of the pulse profile. Along with the absence of correlation of the line energy with luminosity, this could be explained in the framework of the recently proposed "reflection" model for CRSF formation. However more detailed modelling of both line and continuum formation are required to confirm this interpretation.

References in corpus (13)

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• A reflection model for the cyclotron lines in the spectra of X-ray pulsars
• Study of the accreting pulsar 4U 0115+634 with a bulk and thermal Comptonization model
• XTE J1946+274 = GRO J1944+26: An Enigmatic Be/X-ray Binary
• The BeppoSAX 0.1 - 100 keV Spectrum of the X-ray Pulsar 4U 1538-52
• A double-peaked outburst of A 0535+26 observed with INTEGRAL, RXTE, and Suzaku
• Discovery of a Cyclotron Resonance Scattering Feature in the X-ray Spectrum of XTE J1946+274
• Formation of phase lags at the cyclotron energies in the pulse profiles of magnetized, accreting neutron stars
• Measurements of Cyclotron Features and Pulse Periods in the High-Mass X-Ray Binaries 4U 1538-522 and 4U 1907+09 with INTEGRAL
• 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
• The identification of the optical/IR counterpart of the 15.8-s transient X-ray pulsar XTE J1946+274
• The reawakening of the sleeping X-ray pulsar XTE J1946+274
• The Transient Accereting X-Ray Pulsar XTE J1946+274: Stability of the X-Ray Properties at Low Flux and Updated Orbital Solution

Cited by in corpus (8)

• The Ups & Downs of Accreting X-Ray Pulsars: Decade-long observations with the Fermi Gamma-Ray Burst Monitor
• RX J0440.9+4431: another supercritical X-ray pulsar
• XMM-Newton spectroscopy of the accreting magnetar candidate 4U0114+65
• Discovery of a pulse-phase-transient cyclotron line in the X-ray pulsar Swift J1808.4-1754 and identification of an optical companion
• AstroSat observations of the Be/X-ray binary XTE J1946+274 during 2018 and 2021 outbursts
• Study of the X-ray Pulsar XTE J1946+274 with NuSTAR
• Spectral analysis of ultraluminous X-ray pulsars with models of X-ray pulsars
• Constraints on the magnetic field structure in accreting compact objects from aperiodic variability