New ‘black widow’ millisecond pulsar discovered

Multi-band radio pulse profiles of PSR J1555-2908. Credit: Ray et al., 2022.

An international team of astronomers reports the detection of a new millisecond pulsar (MSP) using the Green Bank Telescope (GBT). The newfound pulsar, designated PSR J1555−2908, turns out to be one of the so-called “black widow” MSPs. The finding is detailed in a paper published February 10 on arXiv.org.

A class of extreme binary pulsars with semi-degenerate companion stars is dubbed “spider pulsars.” These objects are further categorized as “black widows” if the companion has extremely low mass (less than 0.1 solar masses), while they are called “redbacks” if the secondary star is heavier.

GBT observations identified radio pulsations of PSR J1555−2908 with a 1.79 ms period. Afterward a 5-minute GBT observation at S-band confirmed the discovery and determined the pulse width at 559.4 Hz to be very narrow—about 3%. By analyzing the Fermi data, gamma-ray pulsations have been also detected from this source.

According to the study, PSR J1555−2908 is an interacting binary system with an orbital period of approximately 0.23 days. The neutron star’s mass is estimated to be some 1.4 solar masses, while the minimum mass of the companion star was calculated to be about 0.052 solar masses. These results indicate the “black widow” class of this MSP.

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