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

TL;DR

Towards resolving the GC pulsar census, the paper presents one of the deepest high-frequency pulsar searches toward the GC to date using the GBT in the X-band. The authors apply Fourier-domain periodicity searches with constant and linearly changing acceleration to reach L_min ≈ 0.14 mJy kpc^2 for CPs and L_min ≈ 0.26 mJy kpc^2 for MSPs, enabling sensitivity to the most luminous GC pulsars. They identify a promising MSP candidate with P = 8.19 ms and DM = 2775 pc cm^-3, detected at S_min ≈ 0.007 mJy and persisting across a 1-hr scan, but not confirmed in follow-up. To robustly assess significance, they introduce a novel data-randomization framework incorporating Kolmogorov–Smirnov tests and flux–DM behavior. The lack of a definitive detection strengthens the GC pulsar missing population problem and supports the view that extreme scattering and/or tight orbital dynamics obscure GC pulsars, informing future observing strategies and follow-up efforts.

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.

Figures (1)

• Figure 1: Pointings at GBT X-band ($1\hbox{$.\mkern-4mu^\prime$}4$ beam width) for the BL--GC survey with an overlaid 1.28 GHz MeerKAT total intensity mosaic of the GC Heywood_2022. The central pointing, labeled as A00, indicates the deep pointing of the GC ($l=0$°, $b=0$°). The black diamond represents the location of the known GC magnetar, J1745$-$2900, near the SMBH Sgr A*. The black cross shows the centroid of the 4FGL J1745.6$-$2859 GC source from the fourth Fermi--LAT catalog, with the dashed blue circle showing its 95% positional uncertainty (a radius of of 37 $^{\prime\prime}$). The rest of the 36 pointings fully sample the wider $\sim 8 \hbox{$^\prime$}$ diameter of the GC bulge region and represent our short 5-min pointings. The gray-shaded pointings show two separate pairs for our ON-OFF observations; A00--D01 and A00--D10. Due to our odd numbered pointings, A00 is the only pointing which is repeated in a pair. The black points in the center of the beams show the beam centers.