Phase-resolved spectroscopy of the accreting millisecond X-ray pulsar SAX J1808.4-3658 during the 2008 outburst
Cornelisse, R., D’Avanzo, P., Muñoz-Darias, T., Campana, S., Casares, J., Charles, Philip A., Steeghs, D., Israel, G. L. and Stella, L.. (2009) Phase-resolved spectroscopy of the accreting millisecond X-ray pulsar SAX J1808.4-3658 during the 2008 outburst. Astronomy & Astrophysics, Vol.495 (No.1). L1-L4. ISSN 0004-6361
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Official URL: http://dx.doi.org/10.1051/0004-6361:200811396
Aims. We obtained phase-resolved spectroscopy of the accreting millisecond X-ray pulsar SAX J1808.4-3658 during its outburst in 2008 to find a signature of the donor star, constrain its radial velocity semi-amplitude (K2), and derive estimates for the pulsar mass.
Methods. Using Doppler images of the Bowen region, we find a significant (≥8σ) compact spot at a position where the donor star is expected. If this is a signature of the donor star, we measure Kem = 248 ± 20 km s−1 (1σ confidence), which represents a strict lower limit to K2. Also, the Doppler map of He II λ4686 shows the characteristic signature of the accretion disc, and there is a hint of
enhanced emission that may be a result of tidal distortions in the accretion disc that are expected in very low mass-ratio interacting binaries.
Results. The lower limit on K2 leads to a lower limit on the mass function of f (M1) ≥ 0.10 M. Applying the maximum K-correction gives 228 < K2 < 322 km s−1 and a mass ratio of 0.051 < q < 0.072.
Conclusions. Despite the limited S/N of the data, we were able to detect a signature of the donor star in SAXJ1808.4−3658, although future observations during a new outburst are still needed to confirm this. If the derived Kem is correct, the largest uncertainty in determining of the mass of the neutron star in SAXJ1808.4-3658 using dynamical studies lies with the poorly known inclination.
|Item Type:||Journal Article|
|Subjects:||Q Science > QB Astronomy|
|Divisions:||Faculty of Science > Physics|
|Library of Congress Subject Headings (LCSH):||Pulsars, X-ray sources, Galactic -- Accretion, Double stars -- Motion in line of sight, Double stars -- Masses|
|Journal or Publication Title:||Astronomy & Astrophysics|
|Official Date:||February 2009|
|Access rights to Published version:||Open Access|
|Funder:||Spain. Ministerio de Ciencia e Innovación (MICINN), Science and Technology Facilities Council (Great Britain) (STFC), Spain. Ministerio de Ciencia y Tecnología (MCT), Spain. Ministerio de Educación y Ciencia (MEC)|
|Grant number:||RYC-2007-01046 (Ramon y Cajal), AYA2007-66887 (MCT), CSD2006-00070 (MEC)|
Bildsten, L., & Chakrabarty, D. 2001, ApJ, 557, 292
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