0000000000243129
AUTHOR
R Iaria
MAXI J1957+032: a new accreting millisecond X-ray pulsar in an ultra-compact binary
The detection of coherent X-ray pulsations at ~314 Hz (3.2 ms) classifies MAXI J1957+032 as a fast-rotating, accreting neutron star. We present the temporal and spectral analysis performed using NICER observations collected during the latest outburst of the source. Doppler modulation of the X-ray pulsation revealed the ultra-compact nature of the binary system characterised by an orbital period of ~1 hour and a projected semi-major axis of 14 lt-ms. The neutron star binary mass function suggests a minimum donor mass of 1.7e-2 Msun, assuming a neutron star mass of 1.4 Msun and a binary inclination angle lower than 60 degrees. This assumption is supported by the lack of eclipses or dips in th…
On the peculiar long-term orbital evolution of the eclipsing accreting millisecond X-ray pulsar SWIFT J1749.4-2807
We present the pulsar timing analysis of the accreting millisecond X-ray pulsar SWIFT J1749.4-2807 monitored by NICER and XMM-Newton during its latest outburst after almost eleven years of quiescence. From the coherent timing analysis of the pulse profiles, we updated the orbital ephemerides of the system. Large phase jumps of the fundamental frequency phase of the signal are visible during the outburst, consistent with what was observed during the previous outburst. Moreover, we report on the marginally significant evidence for non-zero eccentricity ($e\simeq 4\times 10^{-5}$) obtained independently from the analysis of both the 2021 and 2010 outbursts and we discuss possible compatible sc…
Spectral analysis of the AMXP during its 2018 outburst
The Accreting Millisecond X-ray Pulsar IGR J17591-2342 is a Low Mass X-ray Binary (LMXB) system that went in outburst on 2018 August and it was monitored by the NICER observatory and partially by other facilities. We aim to study how the spectral emission of this source evolved during the outburst by exploiting the whole X-ray data repository of simultaneous observations. The continuum emission of the combined broad-band spectra is on average well described by an absorbed Comptonization component scattering blackbody-distributed photons peaking at (0.8 +/- 0.5) keV by a moderately optically thick corona (tau = 2.3 +/- 0.5) with temperature of (34 +/- 9) keV. A blackbody component with tempe…
Outflows and spectral evolution in the eclipsing AMXP SWIFT J1749.4–2807 with NICER, XMM-Newton, and NuSTAR
The neutron star low-mass X-ray binary SWIFT J1749.4–2807 is the only known eclipsing accreting millisecond X-ray pulsar. In this manuscript, we perform a spectral characterization of the system throughout its 2021, 2-week-long outburst, analysing 11 NICER observations and quasi-simultaneous XMM-Newton and NuSTAR single observations at the outburst peak. The broad-band spectrum is well-modelled with a blackbody component with a temperature of ∼0.6 keV, most likely consistent with a hotspot on the neutron star surface, and a Comptonization spectrum with power-law index Γ ∼ 1.9, arising from a hot corona at ∼12 keV. No direct emission from the disc was found, possibly due to it being too cool…