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

Abstract We report the 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 at X band (8–12 GHz) using data from the Breakthrough Listen initiative. In total, we collected 9.5 hr of data covering the wider <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mn>8</mml:mn> <mml:mo accent="false">′</mml:mo> <mml:mtext/> <mml:mspace width="0.1em"/> <mml:mtext/> <mml:mspace width="0.1em"/> </mml:math> diameter of the GC bulge, and 11 hr on the inner 1 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>′</mml:mi> </mml:mrow> </mml:mover> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">min</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.14</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">mJy</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">kpc</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> for CPs and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">min</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.26</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">mJy</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">kpc</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> for MSPs—sensitive enough to detect the most luminous pulsars expected in the GC. Among 5282 signal candidates, we identify an interesting 8.19 ms MSP candidate (dispersion measure (DM) of 2775 pc cm −3 ), persistent in time and frequency across a 1 hr scan at a flux density of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">min</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.007</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">mJy</mml:mi> </mml:math> . We introduce a novel randomization test for evaluating candidate significance against noise fluctuations, including signal persistence via Kolmogorov–Smirnov tests and flux-versus-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 nondetection 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.