NuSTAR and NICER reveal IGR J17591-2342 as a new accreting millisecond X-ray pulsar

A. Sanna; C. Ferrigno; P. S. Ray; L. Ducci; G. K. Jaisawal; T. Enoto; E. Bozzo; D. Altamirano; T. Di Salvo; T. E. Strohmayer; A. Papitto; A. Riggio; L. Burderi; P. M. Bult; S. Bogdanov; A. F. Gambino; A. Marino; R. Iaria; Z. Arzoumanian; D. Chakrabarty; K. C. Gendreau; S. Guillot; C. B. Markwardt; M. T. Wolff

doi:10.1051/0004-6361/201834160

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arXiv · 1808.10195

NuSTAR and NICER reveal IGR J17591-2342 as a new accreting millisecond X-ray pulsar

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Abstract

We report on the discovery by the Nuclear Spectroscopic Telescope Array (NuSTAR) and the Neutron Star Interior Composition Explorer (NICER) of the accreting millisecond X-ray pulsar IGR J17591-2342, detecting coherent X-ray pulsations around 527.4 Hz (1.9 ms) with a clear Doppler modulation. This implies an orbital period of ~8.8 hours and a projected semi-major axis of ~1.23 lt-s. From the binary mass function, we estimate a minimum companion mass of 0.42 solar masses, obtained assuming a neutron star mass of 1.4 solar masses and an inclination angle lower than 60 degrees, as suggested by the absence of eclipses or dips in the light-curve of the source. The broad-band energy spectrum is dominated by Comptonisation of soft thermal seed photons with a temperature of ~0.7 keV by electrons heated to 21 keV. We also detect black-body-like thermal direct emission compatible with an emission region of a few kilometers and temperature compatible with the seed source of Comptonisation. A weak Gaussian line centered on the iron K-alpha; complex can be interpreted as a signature of disc reflection. A similar spectrum characterises the NICER spectra, measured during the outburst fading.

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A. Sanna, C. Ferrigno, P. S. Ray, L. Ducci, G. K. Jaisawal, T. Enoto, E. Bozzo, D. Altamirano, T. Di Salvo, T. E. Strohmayer, A. Papitto, A. Riggio, L. Burderi, P. M. Bult, S. Bogdanov, A. F. Gambino, A. Marino, R. Iaria, Z. Arzoumanian, D. Chakrabarty, K. C. Gendreau, S. Guillot, C. B. Markwardt, M. T. Wolff. 2018-08-30. NuSTAR and NICER reveal IGR J17591-2342 as a new accreting millisecond X-ray pulsar. https://doi.org/10.1051/0004-6361%2F201834160

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