On the Deepest Search for Galactic Center Pulsars and an Examination of an Intriguing Millisecond Pulsar Candidate

TL;DR

This study conducted an ultra-sensitive pulsar survey of the Galactic Center using the GBT, detecting an intriguing millisecond pulsar candidate but ultimately not confirming it, highlighting ongoing challenges in detecting pulsars in this region.

Contribution

It presents the deepest search to date for Galactic Center pulsars, introduces a novel candidate significance test, and discusses implications for pulsar detection challenges in the GC.

Findings

Detected an 8.19 ms MSP candidate with high significance.

No definitive pulsar detections confirmed in follow-up observations.

Reinforces the difficulty of detecting pulsars in the GC due to scattering and orbital effects.

Abstract

We report results of one of the most sensitive pulsar surveys to date targeting the innermost region of the Galactic Center (GC) using the Robert C. Byrd Green Bank Telescope (GBT) at X-band (8--12GHz) using data from the Breakthrough Listen initiative. In total, we collected 9.5 hr of data covering the wider $\sim 8'$ diameter of the GC bulge, and 11 hr on the inner $1.4'$ region between 2021 May and 2023 December. We conducted a comprehensive Fourier-domain periodicity search targeting both canonical pulsars (CPs) and millisecond pulsars (MSPs), using constant and linearly changing acceleration searches to improve sensitivity to compact binaries. Assuming weak scattering, our searches reached luminosity limits of $L_{\rm min} \approx 0.14~{\rm mJy~kpc^{2}}$ for CPs and $L_{\rm min} \approx 0.26~{\rm mJy~kpc^{2}}$ for MSPs -- sensitive enough to detect the most luminous pulsars expected in the GC. Among 5,282 signal candidates, we identify an interesting 8.19 ms MSP candidate (DM of 2775 pc cm$^{-3}$), persistent in time and frequency across a 1-hr scan at a flux density of $S_{\rm min} \approx 0.007~{\rm mJy}$. We introduce a novel randomization test for evaluating candidate significance against noise fluctuations, including signal persistence via Kolmogorov-Smirnov tests and flux-vs-DM behavior. We are unable to make a definitive claim about the candidate due to a mixed degree of confidence from these tests and, more broadly, its non-detection in subsequent observations. This deepens the ongoing missing pulsar problem in the GC, reinforcing the idea that strong scattering and/or extreme orbital dynamics may obscure pulsar signals in this region.