340 MHz VLITE image of GLIMPSE-C01 from February 27, 2021. Credit: McCarver et al., 2023.
Using Karl G. Jansky’s Very Large Array (VLA), astronomers discovered a millisecond pulsar in the globular cluster GLIMPSE-C01 as part of the VLA Ionosphere and Low-Band Transient Experiment (VLITE). This is the first pulsar ever detected in this cluster. The discovery was reported in a paper published Dec. 18 on the preprint server. arXiv.
Pulsars are highly magnetized rotating neutron stars that emit a beam of electromagnetic radiation from their poles, most often in the form of radio waves. The fastest rotating pulsars, with rotation periods less than 30 milliseconds, are called millisecond pulsars (MSP). Astronomers assume that they form in binary systems when the initially more massive component transforms into a neutron star that then rotates due to accretion of material from the secondary star.
Due to their large stellar densities, globular clusters (GCs) are seen as excellent locations for the formation of MSPs. Their stellar densities are so large that many neutron stars can acquire a companion via binary exchanges.
That’s why a team of astronomers led by Amaris V. McCarver of Texas Tech University in Lubbock, Texas, decided to conduct a radio imaging search to detect pulsars in nearly a hundred GCs. To this end, they analyzed images from VLITE and the VLITE Commensal Sky Survey (VCSS).
“In this paper, we present an extensive search for pulsar candidates in globular clusters using low-frequency radio continuum images,” the researchers wrote.
In total, the team identified 10 sources for the sample of 97 globular clusters. Then, they performed a weighted adjustment using archival and new flux density measurements to determine the spectral index of each source.
The strongest pulsar candidate turned out to be the source of GLIMPSE-C01, a dense and massive intermediate-age GC located about 10,760 light-years from Earth. The source has an extremely steep spectrum and analysis of additional radio, X-ray and infrared data confirmed its pulsar nature.
The new pulsar, designated GLIMPSE-C01A, has a rotation period of 19.78 milliseconds and a dispersion measurement of 491.1 pc/cm3. It appears that this pulsar has a higher hard X-ray luminosity (2 to 10 keV) than most globular cluster MSPs, while also having a slower rotation period. This suggests a high magnetic field, at a level of 1 billion Gauss. The characteristic age of this pulsar is estimated at 100 million years.
Summarizing the results, the researchers note that it is necessary to perform regular synchronization and establish an orbital and temporal solution for GLIMPSE-C01A in order to obtain more properties of this pulsar. They added that their discovery highlights the effectiveness of spectral index searches for pulsars.
More information:
Amaris V. McCarver et al, A VLITE search for millisecond pulsars in globular clusters: discovery of a pulsar in GLIMPSE-C01, arXiv (2023). DOI: 10.48550/arxiv.2312.11694
Journal information:
arXiv
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Quote: First pulsar detected in the globular cluster GLIMPSE-C01 (December 30, 2023) recovered on January 2, 2024 on
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