Gamma pulses detected by pulsar PSR J1835−3259B

Using NASA’s Fermi space telescope, Chinese astronomers have explored a recently discovered millisecond pulsar known as PSR J1835−3259B. As a result, they identified gamma-ray pulsations from that source. The finding is reported in an article published on June 27 on the arXiv print server.

Pulsars are highly magnetized, rotating neutron stars emitting a beam of electromagnetic radiation. The fastest rotating pulsars, with rotational periods below 30 milliseconds, are known as millisecond pulsars (MSPs). Astronomers assume that they are formed in binary systems when the initially more massive component becomes a neutron star which is then spun up due to accumulation of matter from the secondary star.

PSR J1835−3259B is a newly discovered MSP in the globular mass NGC 6652. It has a spin period of about 1.83 milliseconds and is in an almost circular orbit of about 28.7 hours within the cluster. The distance to the pulsar is estimated to be about 32,600 light-years.

Considering that NGC 6652 exhibits a detectable gamma-ray emission, a team of astronomers led by Pengfei Zhang of Yunnan University in Kunming, China, inspected PSR J1835−3259B, hoping to discover such an emission from this pulsar as well. For this purpose, they analyzed the data from Fermi’s Large Area Telescope (LAT).

“We performed a temporal analysis of the LAT data based on the PSE radioactivity J1835-3259B (Gautam et al. 2022) to look for possible gamma-ray pulsations,” the researchers wrote in the paper.

Based on the Fermi-LAT data collected for NGC 6652 over a period of approximately 14 years, Zhang’s team was able to detect a gamma-ray pulsation of PSR J1835−3259B. The results indicate a high similarity of the gamma-ray pulse profile of this MSP with the radio.

Astronomers assume that the observed gamma-ray emission at NGC 6652 originates mostly from PSR J1835−3259B. Given that there is no obvious extrapulse phase interval in the pulse profile and also the gamma-ray emission is weak, the scientists could not determine whether there is a probable emission of other MSPs in NGC 6652.

Therefore, according to the authors of the paper, this would be a similar case to globular clusters NGC 6624 and NGC 6626, as in these GCs one exceptionally bright MSP contributes predominantly to the observed gamma-ray emission. The researchers noted that if this scenario is true, PSR J1835−3259B would have a gamma-ray luminosity at a level of 50 decillion erg / s and a gamma-ray efficiency of approximately 0.12.

“Based on different studies of the sources in the GC, the observed γ-ray emission of the GC could primarily arise from this MSP, as in the previous two cases the GCs NGC 6624 and NGC 6626,” the astronomers concluded.

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