A. Papitto, E. Bozzo, C. Ferrigno, T. M. Belloni, L. Burderi, T. Di Salvo, A. Riggio, A. D'Aì, R. Iaria
We report on the detection of a 400.99018734(1) Hz coherent signal in the
Rossi X-ray Timing Explorer light curves of the recently discovered X-ray
transient, IGR J17498-2921. By analysing the frequency modulation caused by the
orbital motion observed between August 13 and September 8, 2011, we derive an
orbital solution for the binary system with a period of 3.8432275(3) hr. The
measured mass function, f(M_2, M_1, i)=0.00203807(8) Msun, allows to set a
lower limit of 0.17 Msun on the mass of the companion star, while an upper
limit of 0.48 Msun is set by imposing that the companion star does not overfill
its Roche lobe. We observe a marginally significant evolution of the signal
frequency at an average rate of -(6.3 +/- 1.9)E-14 Hz/s. The low statistical
significance of this measurement and the possible presence of timing noise
hampers a firm detection of any evolution of the neutron star spin. We also
present an analysis of the spectral properties of IGR J17498-2921 based on the
observations performed by the Swift-X-ray Telescope and the RXTE-Proportional
Counter Array between August 12 and September 22, 2011. During most of the
outburst, the spectra are modeled by a power-law with an index Gamma~1.7-2,
while values of ~3 are observed as the source fades into quiescence.
View original:
http://arxiv.org/abs/1111.1976
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