System mass constraints for the accreting millisecond pulsar XTE J1814-338 using Bowen fluorescence

Wang, L.; Steeghs, D.; Casares, J.; Charles, P.A.; Muñoz-Darias, T.; Marsh, T.R.; Hynes, R.I.; O'Brien, K.

Abstract

We present phase-resolved spectroscopy of the millisecond X-ray pulsar XTE J1814-338 obtained during its 2003 outburst. The spectra are dominated by high-excitation emission lines of He II λ4686, Hβ, and the Bowen blend C III/N III 4630–50 Å. We exploit the proven Bowen fluorescence technique to establish a complete set of dynamical system parameter constraints using bootstrap Doppler tomography, a first for an accreting millisecond X-ray pulsar binary. The reconstructed Doppler map of the N III λ4640 Bowen transition exhibits a statistically significant (>4σ) spot feature at the expected position of the companion star. If this feature is driven by irradiation of the surface of the Roche lobe filling companion, we derive a strict lower limit to the true radial velocity semi-amplitude K2. Combining our donor constraint with the well-constrained orbit of the neutron star leads to a determination of the binary mass ratio: q = 0.123+0.012−0.010 . The component masses are not tightly constrained given our lack of knowledge of the binary inclination. We cannot rule out a canonical neutron star mass of 1.4 M⊙ (1.1 M⊙ < M1 < 3.1 M⊙; 95 per cent). The 68/95 per cent confidence limits of M2 are consistent with the companion being a significantly bloated, M-type main-sequence star. Our findings, combined with results from studies of the quiescent optical counterpart of XTE J1814-338, suggest the presence of a rotation-powered millisecond pulsar in XTE J1814-338 during an X-ray quiescent state. The companion mass is typical of the so-called redback pulsar binary systems (M2 ∼ 0.2 M⊙).

Citation

Wang, L., Steeghs, D., Casares, J., Charles, P., Muñoz-Darias, T., Marsh, T., …O'Brien, K. (2017). System mass constraints for the accreting millisecond pulsar XTE J1814-338 using Bowen fluorescence. Monthly Notices of the Royal Astronomical Society, 466(2), 2261-2271. https://doi.org/10.1093/mnras/stw3312

• Journal Article Type: Article
• Acceptance Date: Dec 15, 2016
• Online Publication Date: Apr 11, 2017
• Publication Date: Apr 11, 2017
• Deposit Date: Apr 9, 2018
• Publicly Available Date: Apr 18, 2018
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 466
• Issue: 2
• Pages: 2261-2271
• DOI: https://doi.org/10.1093/mnras/stw3312