Fermi data confirm gamma-ray pulsations from extreme millisecond pulsar PSR J0435+3233

Chinese astronomers analyzing NASA Fermi Large Area Telescope data have detected gamma-ray pulsations from millisecond pulsar PSR J0435+3233, establishing a gamma-ray counterpart for the source, Phys.org reported based on an arXiv paper. A team led by Mengqing Zhang of Yunnan University examined about 17.7 years of Fermi-LAT observations from 0.1 to 500 GeV. They identified gamma-ray source 4FGL J0435.5+3232 only 0.01 degrees from the pulsar's radio timing position and found pulsations at the spin period. PSR J0435+3233 was discovered in 2026 with China's FAST radio telescope. Phys.org said it is a binary millisecond pulsar about 3,900 light years away with a spin period of roughly 3.2 milliseconds, an exceptionally large period derivative, and spin-down luminosity of 58.9 undecillion erg/s, levels more often associated with young energetic pulsars. Gamma-ray emission was concentrated mainly in rotational phase 0.44 to 0.69, with no significant off-pulse detection. The team measured gamma-ray luminosity of 0.626 decillion erg/s and an inferred apparent gamma-ray efficiency of only 0.00001, alongside a surface dipole magnetic field around 12.6 billion Gauss. The authors wrote that the combination of high spin-down power and low apparent gamma-ray efficiency offers a probe of particle acceleration, radiation beaming, and viewing geometry in extreme millisecond pulsar magnetospheres. The preprint is listed as arXiv:2607.16119 with DOI 10.48550/arxiv.2607.16119.