Detection and timing of gamma-ray pulsations from the $707$ Hz pulsar J0952$-$0607

The Low-Frequency Array radio telescope discovered the $707$ Hz binary millisecond pulsar (MSP) J0952$-$0607 in a targeted radio pulsation search of an unidentified $\mathit{\text{Fermi}}$ gamma-ray source. This source shows a weak energy flux of $F_\gamma = 2.6 \times 10^{-12},$\text{erg}$,$\text{cm}$^{-2},$\text{s}$^{-1}$ in the energy range between $100\text{MeV}$ and $100\text{GeV}$. Here we report the detection of pulsed gamma-ray emission from PSR$$J0952$-$0607 in a very sensitive gamma-ray pulsation search. The pulsar’s rotational, binary, and astrometric properties are measured over seven years of $\mathit{\text{Fermi}}$-Large Area Telescope data. For this we take into account the uncertainty on the shape of the gamma-ray pulse profile. We present an updated radio-timing solution now spanning more than two years and show results from optical modeling of the black-widow-type companion based on new multi-band photometric data taken with HiPERCAM on the Gran Telescopio Canarias on La Palma and ULTRACAM on the New Technology Telescope at ESO La Silla. PSR$$J0952$-$0607 is now the fastest-spinning pulsar for which the intrinsic spin-down rate has been reliably constrained ($\dot{P}_$\text{int}$ \lesssim 4.6 \times 10^{-21},$\text{s}$,$\text{s}$^{-1}$). The inferred surface magnetic field strength of $B_{\text{surf}}\lesssim 8.2\times {10}^7\text{G}$ is among the ten lowest of all known pulsars. This discovery is another example of an extremely fast spinning black-widow pulsar hiding within an unidentified $$\mathit{\text{Fermi}}$ gamma-ray source. In the future such systems might help to pin down the maximum spin frequency and the minimum surface magnetic field strength of MSPs.