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Astronomers have employed the Nuclear Spectroscopic Telescope Array (NuSTAR) and the Neutron Star Interior Composition Explorer (NICER) to observe the X-ray pulsar RX J0032.9-7348 in a broadband X-ray energy range. Results of the observational campaign, April 30 on the arXiv preprint server, yield important insights into the properties of this pulsar.

Pulsars are rapidly rotating neutron stars with strong magnetic fields that emit beams of electromagnetic radiation. While they are most commonly detected as brief bursts of radio waves, some pulsars can also be observed in optical, X-ray, and gamma-ray wavelengths.

Accretion-powered X-ray pulsars (XRPs) are magnetized neutron stars found in X-ray binary (XRB) systems. They produce X-rays by accreting mass from their companion star.

RX J0032.9-7348 was first identified as an X-ray transient source in the Small Magellanic Cloud (SMC) about 30 years ago. It experienced an X-ray brightening in October 2024 and recent observations have detected X-ray pulsation with a period of approximately 7.02 seconds, which allowed astronomers to classify this source as an XRP.

However, although RX J0032.9-7348 has been known for decades, very little is known regarding its properties and its optical counterpart has not been identified. Therefore, a team of astronomers led by Birendra Chhotaray of the Â鶹ÒùÔºical Research Laboratory (PRL) in Ahmedabad, India, decided to take a closer look at this pulsar with NuSTAR and NICER.

"Following the reported X-ray brightening of the source, we proposed a Target of Opportunity (ToO) observation with NuSTAR, which was carried out on November 17, 2024 for an exposure of ≈25 ks. We also monitored the source with NICER to investigate the timing and spectral properties of the source," the researchers wrote.

The observations conducted by Chhotaray's team confirmed the X-ray pulsation period of RX J0032.9-7348 and found that its pulse profile across a broad energy range is double-peaked, with moderate variations observed as a function of energy.

During the observations, the spin period of RX J0032.9-7348 increased at a rate of approximately -0.00033 seconds per day. This spin-up suggests that the pulsar gained angular momentum, likely due to accretion processes during the X-ray brightening phase. While the orbital period of the binary is still unknown, the astronomers estimated that it may be within the range of 20–30 days.

Furthermore, it turned out that the luminosity of the pulsar varied from 8.2 undecillion to 37 undecillion erg/s during the monitoring campaign. The researchers report that no evidence of iron emission line or cyclotron resonance scattering features was found in the energy spectrum of this source.

When it comes to the magnetic field of RX J0032.9-7348, the authors of the paper estimated that it should be between 0.14 and 3.2 trillion Gauss, assuming a limiting luminosity at a level of 0.01–5.0 undecillion erg/s.

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