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Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
Abstract:
Redbacks are millisecond pulsar binaries with low mass, irradiated
companions. These systems have a rich phenomenology that can be used to probe
binary evolution models, pulsar wind physics, and the neutron star mass
distribution. A number of high-confidence redback candidates have been
identified through searches for variable optical and X-ray sources within the
localisation regions of unidentified but pulsar-like Fermi-LAT gamma-ray
sources. However, these candidates remain unconfirmed until pulsations are
detected. As part of the TRAPUM project, we searched for radio pulsations from
six of these redback candidates with MeerKAT. We discovered three new radio
millisecond pulsars, PSRs J0838$-$2527, J0955$-$3947 and J2333$-$5526,
confirming their redback nature. PSR J0838$-$2827 remained undetected for two
years after our discovery despite repeated observations, likely due to
evaporated material absorbing the radio emission for long periods of time.
While, to our knowledge, this system has not undergone a transition to an
accreting state, the disappearance, likely caused by extreme eclipses,
illustrates the transient nature of spider pulsars and the heavy selection bias
in uncovering their radio population. Radio timing enabled the detection of
gamma-ray pulsations from all three pulsars, from which we obtained 15-year
timing solutions. All of these sources exhibit complex orbital period
variations consistent with gravitational quadrupole moment variations in the
companion stars. These timing solutions also constrain the binary mass ratios,
allowing us to narrow down the pulsar masses. We find that PSR J2333$-$5526 may
have a neutron star mass in excess of 2 M$_{\odot}$.
