2026/07/17 by Mengqing Zhang, Shengbin Pei, Pengfei Zhang
#astro-ph.HE
Motivated by the recent discovery of PSR~J0435+3233, a millisecond pulsar with an exceptionally large period derivative of P=4.9×10-17 \rm s s-1 and a high spin-down luminosity of E=5.89×1037 \rm erg s-1, we analyze ∼17~yr of observations obtained with the Fermi Large Area Telescope for the pulsar. We identify the cataloged source 4FGL~J0435.5+3232, located only 0.01∘ from the radio timing position, as the γ-ray counterpart of PSR~J0435+3233. Using γ-ray events collected within the validity interval of the radio timing ephemeris, we detect its γ-ray pulsations at a ∼6.8σ confidence level. In this interval, the phase-resolved analysis shows that the pulsed emission is concentrated predominantly within the rotational-phase of ϕ∼0.44--0.69. We also derive its γ-ray luminosity of Lγ=6.26×1032 \rm erg s-1, assuming a distance of 1.2~kpc and isotropic emission. This luminosity corresponds to an apparent γ-ray efficiency of ηγ∼1.1×10-5, revealing an exceptionally low γ-ray output despite the pulsar's young-pulsar-like rotational-energy budget. Our detection establishes PSR~J0435+3233 as a γ-ray MSP, and the striking combination of its high spin-down power and low apparent γ-ray efficiency provides a new probe of particle acceleration, radiation beaming, and viewing geometry in the magnetospheres of millisecond pulsars with extreme rotational properties.