Volume 617, September 2018
|Number of page(s)||5|
|Section||Letters to the Editor|
|Published online||01 October 2018|
Letter to the Editor
NuSTAR and NICER reveal IGR J17591–2342 as a new accreting millisecond X-ray pulsar
Dipartimento di Fisica, Università degli Studi di Cagliari, SP Monserrato-Sestu km 0.7, 09042 Monserrato, Italy
2 ISDC, Department of Astronomy, University of Geneva, Chemin d’Écogia 16, 1290 Versoix, Switzerland
3 Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352, USA
4 Institut für Astronomie und Astrophysik, Eberhard Karls Universität, Sand 1, 72076 Tübingen, Germany
5 National Space Institute, Technical University of Denmark, Elektrovej 327-328, 2800 Lyngby, Denmark
6 Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto, Kyoto 606-8502, Japan
7 The Hakubi Center for Advanced Research, Kyoto University, Yoshida-Ushinomiya-cho, Sakyo-ku, Kyoto 606-8302, Japan
8 Physics & Astronomy, University of Southampton, Southampton, Hampshire SO17 1BJ, UK
9 Università degli Studi di Palermo, Dipartimento di Fisica e Chimica, via Archirafi 36, 90123 Palermo, Italy
10 Astrophysics Science Division, NASA’s Goddard Space Flight Center, Greenbelt, MD 20771, USA
11 INAF, Osservatorio Astronomico di Roma, Via di Frascati 33, 00044 Monteporzio Catone (Roma), Italy
12 Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA
13 INAF/IASF Palermo, via Ugo La Malfa 153, 90146 Palermo, Italy
14 IRAP, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France
15 MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
16 CNRS, IRAP, 9 avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
17 Université de Toulouse, CNES, UPS-OMP, 31028 Toulouse, France
Accepted: 10 September 2018
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 M⊙ 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
© ESO 2018
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