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New Insights into the Millisecond Pulsar Binary PSR J1431−4715
Recent X-ray observations of the millisecond pulsar binary PSR J1431−4715, conducted by European astronomers using the European Space Agency (ESA) XMM-Newton satellite, have unveiled significant insights into this intriguing system. The findings of the research, led by astronomer Domitilla de Martino from the Astronomical Observatory of Capodimonte in Naples, have been detailed in a study published on September 3 on the pre-print server arXiv.
Pulsars, which are rapidly rotating neutron stars that emit beams of electromagnetic radiation, are classified based on their rotation periods. Millisecond pulsars (MSPs), like J1431, have exceptionally short spin periods of less than 30 milliseconds. Their formation is generally believed to occur in binary systems, where a more massive star evolves into a neutron star and subsequently gains angular momentum through the accretion of matter from its companion star.
Within the fascinating category of binary pulsars, those with semi-degenerate companion stars are referred to as “spider pulsars.” These spiders can be further categorized into “black widows,” which have very low-mass companions (under 0.1 solar masses), and “redbacks,” which feature companions of greater mass.
Situated between 5,250 and 8,400 light years away from Earth, PSR J1431−4715 is noted for its rapid spin period of just 2.01 milliseconds and a spin-down power measuring 68 decillion erg/s, making it one of the most dynamic and energetic pulsars known. Previous studies indicated that its radio emissions are significantly affected by strong eclipses that occur at the binary’s orbital period of approximately 10.8 hours. Also, the system was found to host a non-degenerate donor star with a minimum mass of 0.12 solar masses, which earned it the classification of a redback pulsar.
Despite its discovery in 2015, PSR J1431 has received limited attention in terms of observational studies. To rectify this, the research team aimed to conduct a thorough investigation focused on the X-ray emissions from J1431, utilizing data from both XMM-Newton and optical photometric observations from the European Southern Observatory’s 3.5m New Technology Telescope (NTT) in Chile.
The results of the observations showed that J1431’s X-ray spectrum appeared featureless and indicative of non-thermal emissions, with a power law photon index of 1.6 and minimal absorption. Notably, a thermal component was also identified, suggesting contributions from the heated polar cap within the softer X-ray spectrum.
Data analysis indicated that the companion star in the J1431 system is an early F-type star with a mass of approximately 0.2 solar masses, reinforcing its classification as a redback. However, the star’s temperatures were found to be higher than typical for redbacks, with dayside and nightside temperatures recorded at around 7,500 K and 7,400 K, respectively.
In terms of system orientation, the astronomers determined that PSR J1431 has a binary inclination of 59 degrees. Additionally, the system is positioned approximately 10,100 light years from Earth, further away than prior estimates suggested. The analysis also hints that the pulsar itself is relatively massive, with an estimated mass ranging between 1.8 and 2.2 solar masses.
More information: D. de Martino et al, X-ray and optical observations of the millisecond pulsar binary PSR J1431−4715, arXiv (2024). DOI: 10.48550/arxiv.2409.02075
Journal information: arXiv (arxiv.org)
Source
phys.org