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

• Main Authors: Sanna, A. (Author), Ferrigno, C. (Author), Ray, P. S. (Author), Ducci, L. (Author), Jaisawal, G. K. (Author), Enoto, T. (Author), Bozzo, E. (Author), Altamirano, D. (Author), Di Salvo, T. (Author), Strohmayer, T. E. (Author), Papitto, A. (Author), Riggio, A. (Author), Burderi, L. (Author), Bult, P. M. (Author), Bogdanov, S. (Author), Gambino, A. F. (Author), Marino, A. (Author), Iaria, R. (Author), Arzoumanian, Z. (Author), Gendreau, K. C. (Author), Guillot, S. (Author), Markwardt, C. (Author), Wolff, M. T. (Author), Chakrabarty, Deepto (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Physics (Contributor)
• Format: Article
• Language: English
• Published: EDP Sciences, 2019-03-18T14:42:41Z.
• Subjects: Article
• Online Access: Get fulltext

We report 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. Coherent X-ray pulsations around 527.4 Hz (1.9 ms) with a clear Doppler modulation were detected. This implies an orbital period of ∼8.8 h and a projected semi-major axis of ∼1.23 lt-s. With the binary mass function, we estimate a minimum companion mass of 0.42 M, obtained assuming a neutron star mass of 1.4[subscript ⊙] and an inclination angle lower than 60°, as suggested by the absence of eclipses or dips in the light curve of the source. The broad-band energy spectrum, obtained by combining NuSTAR, swift and INTEGRAL observations, 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 that is compatible with an emission region of a few kilometers and a temperature compatible with the seed source of Comptonisation. A weak Gaussian line centred on the iron Kα complex can be interpreted as a signature of disc reflection. A similar spectrum characterises the NICER spectra, which was measured when the outburst faded. Key words: accretion, accretion disks / stars: low-mass / pulsars: general / stars: neutron / X-rays: binaries
United States. National Aeronautics and Space Administration