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Insights into Transitional Millisecond Pulsar PSR J1023+0038
A team of astronomers from Italy and Spain has made significant advancements in the study of the transitional millisecond pulsar PSR J1023+0038 using the Gran Telescopio Canarias (GTC). Their findings, published on September 19 in research made available on arXiv, offer valuable insights into the characteristics and behavior of this intriguing celestial object.
Pulsars, which are highly magnetized neutron stars, emit beams of electromagnetic radiation while rotating. Among them, millisecond pulsars (MSPs)—those with rotation periods under 30 milliseconds—are particularly notable for their rapid spins. The current understanding suggests that MSPs form in binary systems when a massive star evolves into a neutron star and subsequently gains rotational speed through the accretion of matter from a companion star.
Transitional millisecond pulsars (tMSPs) are a rare subclass of pulsars that alternate between a rotation-powered state, characterized by radio emissions, and a disk state featuring X-ray pulsations accompanied by distinct optical spectral traits. To date, only three such pulsars have been identified, including J1023, which was first discovered approximately twenty years ago. This pulsar boasts a spin period of 1.69 milliseconds and orbits a late-type star, classified as G5, with an orbital period of about 4.75 hours.
Previously, J1023 has shown that it can transition between X-ray states and those governed by rotational radio emissions. In their recent study, led by Marco Messa from the University of Milan, the researchers utilized the OSIRIS (Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy) instrument at GTC to delve deeper into the properties of this pulsar.
The new observations revealed significant short-term flux variability across all wavelengths in J1023, with changes manifesting over seconds. Additionally, the study discovered notable variability in the properties of emission lines, such as equivalent width and full width at half maximum, occurring over minutes. This marks an important first in the study of tMSPs, as previous data had not documented such rapid changes in spectral line properties.
The variations in the observed continuum and spectral line features appeared random and did not demonstrate correlation, leaving researchers puzzled regarding their underlying mechanisms. Furthermore, the Balmer and helium series emission lines exhibited double-horned profiles, suggesting the presence of an accretion disk, which implies that J1023 was likely in its disk state during the observation period.
In conclusion, the authors recommend further multi-wavelength observations to explore potential correlations between the variability of emission line characteristics and the switching behaviors inherent in J1023. Such investigations could deepen the understanding of the dynamic processes at play in transitional millisecond pulsars.
More information: M. M. Messa et al, High-temporal-resolution optical spectroscopic observations of the transitional millisecond pulsar PSR J1023+0038, arXiv (2024). DOI: 10.48550/arxiv.2409.12893
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phys.org