Nustar-FPMA Image of all observations used, in the energy range 3 to 50 Kev. The location of the source, SXP 138, is indicated by a circular region. Credit: arxiv (2025). DOI: 10.48550 / Arxiv. 2004.07219
Using the NASA nuclear nuclear spectroscopic telescope network (NUSAR), Indian astronomers have observed a binary XP 138 X -ray system. Results of Nustar observations, published on March 26 onarxiv Pre-printed server, give important information regarding the behavior of this system.
The X -ray binary are made up of a normal star or a white dwarf transferring the mass to a compact neutron star or a black hole. Based on the mass of the companion star, astronomers divide them into low -mass x -ray binary (LMXB) and high -mass ray binary (HMXB).
BITIES BE / RAY (BE / XRBS) are the largest subgroup of HMXBS. These systems consist of BE stars and, generally, neutron stars, including pulsars. Observations have revealed that most of these systems have a low persistent X -ray emission which is interrupted by explosions that last several weeks.
SXP 138 is a BE / XRB in the small Magellanic (SMC) cloud containing a pulsar with a 138 -second rotation period. The orbital period of the system proved to be around 125 days. In addition, previous observations have noted that SXP 138 also displays a superorbital period of around 1,000 days, which could be caused by stochastic changes in the accretion disk.
A team of astronomers led by Soham Pravin Sanyashiv of the Indian Institute of Science Education and Research Kolkata, more closely examined SXP 138 and its frequency using telescopes on nustar – FPMA and FPMB.
The observations have enabled the Sanyashiv team to better understand the evolution of the spin, the nature of the pulse profile and the spectral characteristics of SXP 138.
By analyzing the light curve of SXP 138, it turned out that the pulsar spin period increased from 140.69 to 140.85 seconds between August 2016 and August 2017. This suggests that the source is in the propeller regime in which the magnetospheric radius exceeds the radius of carrotation, preventing effective accretion on the surface of the neutrron star.
The SXP 138 pulse profile has a complex structure. In most observations, two high peaks with positive peaks and two secondary peaks with a negative normalized intensity are distinguished.
Astronomers explain that high peaks point to the pencil beam from asymmetrical hot spots, while the two secondary peaks indicate a complex radiative transfer.
The spectral analysis of SXP 138 revealed that it requires both the black body and the power law components.
“With improved accretion, the black body temperature increases and the power law index decreases, probably due to the heating of the internal disc and the formation of accretion columns,” conclude the authors of the article.
Scientists add that future observations of SXP 138 and similar binaries should focus on monitoring long -term spin variations and the study of spectral state transitions. This could advance our knowledge of accretion processes in such systems.
More information:
Soham Pravin Sanyashiv et al, be binary radiography pulsar sxp 138: non -linear characteristics, impulses and spectral characteristics, arxiv (2025). DOI: 10.48550 / Arxiv. 2004.07219
Newspaper information:
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