We report the discovery of 1.97 ms period gamma-ray pulsations from the 75 minute orbital-period binary pulsar now named PSR J1653−0158. The associated Fermi Large Area Telescope gamma-ray source 4FGL J1653.6−0158 has long been expected to harbor a binary millisecond pulsar. Despite the pulsar-like gamma-ray spectrum and candidate optical/X-ray associations—whose periodic brightness modulations suggested an orbit—no radio pulsations had been found in many searches. The pulsar was discovered by directly searching the gamma-ray data using the GPU-accelerated Einstein@Home distributed volunteer computing system. The multidimensional parameter space was bounded by positional and orbital constraints obtained from the optical counterpart. More sensitive analyses of archival and new radio data using knowledge of the pulsar timing solution yield very stringent upper limits on radio emission. Any radio emission is thus either exceptionally weak, or eclipsed for a large fraction of the time. The pulsar has one of the three lowest inferred surface magnetic-field strengths of any known pulsar with B surf ≈ 4 × 107 G. The resulting mass function, combined with models of the companion star’s optical light curve and spectra, suggests a pulsar mass ≳2 M ⊙. The companion is lightweight with mass ∼0.01 M ⊙, and the orbital period is the shortest known for any rotation-powered binary pulsar. This discovery demonstrates the Fermi Large Area Telescope's potential to discover extreme pulsars that would otherwise remain undetected.

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BES data on J/ψ → γ(K + K − π + π − ) are presented. The K * K * contribution peaks strongly near threshold. It is fitted with a broad 0 −+ resonance with mass M = 1800 ± 100 MeV, width Γ = 500 ± 200 MeV. A broad 2 ++ resonance peaking at 2020 MeV is also required with width ∼ 500 MeV. There is further evidence for a 2 −+ component peaking at 2.55 GeV. The non-K * K * contribution is close to phase space; it peaks at 2.6 GeV and is very different from K * K * .PACS numbers: 14.40. Cs, 12.39.Mk, 13.25.Jx, 13.40.Hq Typeset using REVT E X [4]. There, we also find a broad 2 The analysis in this paper uses 7.8 × 10 6 J/ψ triggers collected by the Beijing Spectrometer(BES). This detector has been described in detail in Ref [12]. Here we describe briefly those detector elements crucial to this measurement. Tracking is provided by a 10 superlayer main drift chamber (MDC). Each superlayer contains four layers of sense wires measuring both the position and the ionization energy loss (dE/dx) of charged particles.The momentum resolution is σ P /P = 1.7% A positive identification of at least one K ± and one π ± is required using time of flight and/or dE/dx. If two tracks are ambiguous, both alternative identifications are tried. Events are fitted kinematically to the 4C hypothesis J/ψ → γ(, requiring a confidence level > 5%. If there is more than one photon, the fit is repeated using all permutations.Events with two or more photons are also fitted to J/ψ → γγKThose giving a better fit than to γ(K + K − π + π − ) are rejected, as are events fitting the final stateNext, we require | U miss |=| E miss − P miss |< 0.12 GeV/c 2 , so as to reject the events with multi-photons or more or less than two charged kaons; here, E miss and P miss are, respectively, the missing energy and missing momentum of all charged particles; they are calculated by assuming the charged particles are(GeV/c) 2 is required in order to remove the background J/ψ → π 0