Title:	Phase-dependent cyclotron line feature in XTE J1946 + 274: a NuSTAR view
Authors:	Devaraj, Ashwin Paul, Biswajit
Keywords:	stars: neutron pulsars binaries X-rays XTE J1946 + 274
Issue Date:	2-Dec-2022
Publisher:	Royal Astronomical Society
Citation:	Monthly Notices of the Royal Astronomical Society, 2022, Vol. 517, p2599
Abstract:	We report the results from a timing and spectral analysis of the Be/X-ray binary, XTE J1946 + 274 which underwent a Type II outburst in June 2018 and was observed with NuSTAR at a flux of ∼2.8 × 10−9 erg cm−2 s−1. The spectrum was described well with HighEC, NPEX, FDcut, and the CompTT models for the continuum. A cyclotron line is detected at ∼37.7 keV independent of the choice of the continuum model, confirming the previous detections. The pulse profile shows strong energy dependence with a double-peaked structure at low energies while evolving into a single-peaked structure at higher energies. Though the cyclotron line is detected in the phase-average spectra, from the phase-resolved analysis we find that it is unambiguously detected in only ∼50 per cent of the phases, where the second pulse peak disappears. In the remaining pulse phase, we find marginal evidence for the presence of a weak line at 36.5 keV. The cyclotron line centroid remains fairly constant with phase in the second peak but a significant variation of the Cyclotron Resonance Scattering Feature's depth with the pulse phase is evident. We compile the results from the previously published literature on this source and find that XTE J1946 + 274 has been observed over the flux range of ∼0.4–7.3 × 10−9 erg cm−2 s−1. Although there is no clear variation between the cyclotron line energy with luminosity, it is among a handful of the sources that have been observed over such a wide range of fluxes and may contain, within this range, the critical luminosity.
Description:	Restricted Access.
URI:	http://hdl.handle.net/2289/8003
ISSN:	0035-8711 1365-2966 (Online)
Alternative Location:	https://ui.adsabs.harvard.edu/abs/2022MNRAS.517.2599D/abstract https://doi.org/10.1093/mnras/stac2806
Copyright:	2022 The Authors(s)
Appears in Collections:	Research Papers (A&A)

Items in RRI Digital Repository are protected by copyright, with all rights reserved, unless otherwise indicated.