Team identifies how interstellar medium impacts pulsar signals

Team identifies how interstellar medium impacts pulsar signals
by Clarence Oxford
Los Angeles CA (SPX) Nov 27, 2024

A new study led by Sofia Sheikh of the SETI Institute has revealed how pulsar signals - emissions from the spinning remnants of massive stars - are distorted as they traverse the interstellar medium (ISM). The findings, published in The Astrophysical Journal, were developed through contributions from undergraduate researchers in Penn State's Pulsar Search Collaboratory, a student program originally founded by Maura McLaughlin of West Virginia University. McLaughlin, a prominent physics and astronomy professor, facilitated access to archival data from the Arecibo Observatory, which served as the backbone for the research.

The team measured scintillation bandwidths for 23 pulsars, with six being previously unexamined, providing new data on how signals are affected by the ISM's charged particles, gas, and dust. Their analysis showed that in nearly all cases, the observed bandwidths exceeded predictions from existing galactic models, underscoring the need for refined ISM density maps.

"This work demonstrates the value of large, archived datasets," explained Dr. Sheikh. "Even years after the Arecibo Observatory's collapse, its data continues to unlock critical information that can advance our understanding of the galaxy and enhance our ability to study phenomena like gravitational waves."

The distortion phenomenon, known as diffractive interstellar scintillation (DISS), results from the same principles of light refraction that cause stars to twinkle or patterns to form on the bottom of a swimming pool. In this case, the "twinkling" occurs due to clouds of charged particles in the ISM. Understanding and accounting for these distortions is vital for precise pulsar timing, a critical component in efforts like NANOGrav's research into the gravitational wave background and its implications for early Universe phenomena.

The study highlighted that galactic models incorporating structures like spiral arms align better with observed DISS data. However, these models performed less accurately for newly discovered pulsars, emphasizing the need for continued updates.

This research, part of the AO327 survey from Arecibo, provides a foundation for ongoing studies. The team plans to analyze data from additional pulsars in the AO327 dataset to refine ISM density models further. Such advancements are expected to support collaborations like NANOGrav, enhancing the precision of pulsar timing array measurements.

This collaborative effort involved contributors from the SETI Institute, Penn State, and the NANOGrav Group at West Virginia University, including Michael Lam of the SETI Institute and former SETI researcher Grayce Brown.

Research Report:Scintillation Bandwidth Measurements from 23 Pulsars from the AO327 Survey