Utilizing the Neutron star Inside Composition Explorer (NICER) onboard the Worldwide Area Station (ISS), European astronomers have carried out spectral evaluation of a low-mass X-ray binary referred to as XTE J1810–189. Outcomes of the research, out there in a analysis paper printed September 13 on the preprint server arXiv, shed extra mild on the spectral evolution of this technique.
X-ray binaries (XRBs) are composed of a traditional star or a white dwarf transferring mass onto a compact neutron star or a black gap. Based mostly on the mass of the companion star, astronomers divide them into low-mass X-ray binaries (LMXBs) and high-mass X-ray binaries (HMXBs).
XTE J1810–189 is a neutron star LMXB estimated to be situated between 11,400 and 28,400 mild years away. It’s a transient supply, which alternates between quiescent phases and durations of elevated X-ray emission as a result of accretion on the neutron star.
In September 2020, an X-ray outburst of XTE J1810–189 began and lasted about three months. A crew of astronomers led by Arianna Manca of the College of Cagliari in Italy, has noticed XTE J1810–189 throughout this outburst in an effort to higher perceive its spectral evolution.
“On this paper, we studied the spectral evolution of the NS LMXB XTE J1810–189 throughout its newest outburst. We analyzed NICER knowledge within the 1–10 keV power vary, modeling the emission with an absorbed, thermally Comptonized part, and with a special mannequin composed by a chilly, Comptonized disk and black physique,” the researchers wrote within the paper.
The astronomers managed to conduct 33 NICER observations of XTE J1810–189 through the 2020 outburst, and 23 of them had an publicity lengthy sufficient to offer enough statistics for spectral evaluation. The research discovered that 22 of those observations might be properly match by an absorbed, thermally Comptonized part whose photon index barely varies in time, reaching its highest worth in direction of the tip of the outburst.
The temperature of the Comptonized black physique was discovered to be about 0.6 keV, which, in accordance with the authors of the paper, can both be a scorching disk or the neutron star floor. Due to this fact, they famous that additional investigation is required to find out whether or not the seed photons for the Comptonization part are coming from the accretion disk or the neutron star.
Based mostly on the collected knowledge, the researchers concluded that XTE J1810–189 didn’t attain a full excessive/delicate state through the three-months lengthy outburst and its highest luminosity was measured to be about one undecillion erg/s. NICER observations additionally revealed the presence of thermonuclear bursts through the outburst part of XTE J1810–189. The astronomers famous that the length of those bursts means that the system incorporates a hydrogen-rich important sequence star.
Extra info:
A. Manca et al, Spectral Evaluation of the LMXB XTE J1810-189 with NICER Information, arXiv (2023). DOI: 10.48550/arxiv.2309.06831
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