Astronomy and Astrophysics, volume 598A, 34-34 (2017/2-1)
Discovery of a new accreting millisecond X-ray pulsar in the globular cluster NGC 2808.
SANNA A., PAPITTO A., BURDERI L., BOZZO E., RIGGIO A., DI SALVO T., FERRIGNO C., REA N. and IARIA R.
Abstract (from CDS):
We report on the discovery of coherent pulsations at a period of 2.9 ms from the X-ray transient MAXI J0911-655 in the globular cluster NGC 2808. We observed X-ray pulsations at a frequency of ∼339.97Hz in three different observations of the source performed with XMM-Newton and NuSTAR during the source outburst. This newly discovered accreting millisecond pulsar is part of an ultra-compact binary system characterised by an orbital period of 44.3-min and a projected semi-major axis of ∼17.6lt-ms. Based on the mass function, we estimate a minimum companion mass of 0.024M☉, which assumes a neutron star mass of 1.4M☉ and a maximum inclination angle of 75° (derived from the lack of eclipses and dips in the light-curve of the source). We find that the Roche-lobe of the companion star could either be filled by a hot (5x106K) pure helium white dwarf with a 0.028M☉ mass (implying i~=58°) or an old (>5Gyr) brown dwarf with metallicity abundances between solar/sub-solar and mass ranging in the interval 0.065 to 0.085 (16<i<21). During the outburst, the broad-band energy spectra are well described by a superposition of a weak black-body component (kT∼0.5keV) and a hard cut-off power-law with photon index Γ∼1.7 and cut-off at a temperature kTe∼130keV. Up until the latest Swift-XRT observation performed on 19th July, 2016, the source had been observed in outburst for almost 150 days, which makes MAXI J0911-655 the second accreting millisecond X-ray pulsar with outburst duration longer than 100 days.
© ESO, 2017
X-rays: binaries - pulsars: general - stars: neutron - accretion, accretion disks - binaries: general
PSR J0023+0038 misprint for PSR J1023+0038. XTE J0299-314 misprint for XTE J0929-314.
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