ar X iv : a st ro - p h / 98 05 35 4 v 1 2 8 M ay 1 99 8 Discovery of a New 89 Second X – ray Pulsar XTE J 1906 + 09
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چکیده
Received ; accepted – 2 – ABSTRACT We report on the discovery of a new pulsating X–ray source during Rossi X–ray Timing Explorer observations of a low galactic latitude field centered at RA (J2000) = 19 hr 05 m 43 s and Dec (J2000)= +08 • 58 ′ 48 ′′. Significant pulsations were detected by both the PCA and HEXTE instruments aboard RXTE at a fundamental period of 89.17 ± 0.02 seconds, with higher harmonics also visible in the 2 − 10 keV power spectrum. The folded lightcurve from the source is multiply peaked at lower energies, and changes to single peaked morphology above ∼ 20 keV. The phase averaged spectrum from the source is well fit by strongly absorbed power law or thermal bremsstrahlung spectral models of photon index 1.9 ± 0.1 or temperature 19.5 ± 4.6 keV, respectively. The mean neutral hydrogen column density is N H ≈ 10 23 cm −2 , suggesting a distance of > 10 kpc to the source and a minimum 2 − 10 keV X–ray luminosity of 2 × 10 35 ergs s −1. By comparison with other pulsars with similar periods and luminosities, we suggest that XTE J1906+09 has a supergiant companion with an underfilled Roche lobe. We speculate further that one of the M stars in a peculiar M star binary system may be the companion.
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