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Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
Abstract:
We report the discovery of 1.97ms-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 multi-dimensional 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 $B_{\rm surf} \approx 4
\times 10^{7}\,$G. The resulting mass function, combined with models of the
companion star's optical light curve and spectra, suggest a pulsar mass
$\gtrsim 2\,M_{\odot}$. The companion is light-weight with mass $\sim
0.01\,M_{\odot}$, 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.
