A Census of Pulsars in Possible Association with Galactic Open Clusters

TL;DR

This work leverages Gaia DR3 to perform a census of pulsars in Galactic open clusters, cross-matching 164 pulsars with 3530 clusters to identify present-day associations and tracing backward orbits to reveal potential birthplaces. By combining independent pulsar distances, cluster kinematics, and Galactic potential integration, the study finds 4 pulsars likely residing in open clusters (notably PSR J1302$-$6350 with UBC 525) and 19 pulsars likely born in open clusters, providing constraints on progenitor environments and natal kicks. The methodology relies on angular proximity thresholds, distance overlaps, and Monte Carlo-based probabilities, with results suggesting that a subset of pulsars originated in clusters prior to cluster dissolution or dispersion. The findings underscore the scientific potential of targeted pulsar searches in open clusters (e.g., with FAST, MeerKAT, SKA) to refine pulsar birth environments and population synthesis models.

Abstract

Among the $\sim 4000$ known pulsars in our Galaxy, $\lesssim 10\%$ are found in globular clusters, but none has been confirmed in any open clusters yet, although they outnumber globular clusters by about 20 times. In this work, we make use of the Gaia DR3 catalog of Galactic open clusters and conduct a pulsar census, in order to identify pulsars that are either 1) current members of open clusters, or 2) escaped from open clusters to the field. Among 164 pulsars with independent distance measurements and 3530 open clusters, we find that 4 pulsars are likely residing in open clusters. In particular, we find compelling evidence that the binary pulsar J1302$-$6350 (B1259$-$63) is a member of the open cluster UBC~525; based on Gaia data, we update its distance to be $2.26\pm 0.07$~kpc and measure the mass of its companion Be star LS 2883 to be $16.8 M_\odot$. For 145 pulsars with both distance and proper motion measurements and 2967 open clusters with full kinematic parameters, we trace the past trajectories of both pulsars and open clusters in the Galactic gravitational potential, and find pulsars that were within 3 times the radius of a cluster. This results in 19 pulsars that were likely born in open clusters. We discuss implications for the formation history of PSR J1302$-$6350 and highlight the scientific potential of searching for pulsars in open clusters.

Figures (8)

• Figure 1: Distance and proper motion distributions for candidate pulsar-open cluster associations. Left panel: Each row represents a pulsar-cluster pair, with open cluster distances shown as blue error bars ($\pm5 \sigma_{\text{oc}}$, where $\sigma_{\text{oc}}$ is the cluster distance uncertainty) and pulsar distances marked by red ($\pm3 \sigma_{\text{psr}}$) and light-red ($\pm5 \sigma_{\text{psr}}$) error bars with $\sigma_{\text{psr}}$ being the pulsar distance uncertainty. Right panel: Proper motion vectors for open clusters (blue arrows) and pulsars (red arrows). Each row corresponds to the pair in the left panel, while segment lengths indicate proper motion magnitudes, and arrows show directions.
• Figure 2: Past trajectories of PSR J0630$-$2834 and its potential birth open clusters -- Collinder 132 and CWNU 45. The '+' symbol marks a 0.5 Myr interval along the paths. Blue (black) lines trace the past trajectories of the clusters, while magenta and green dots indicate the past positions of member stars in Collinder 132 and CWNU 45, respectively. Assuming a radial velocity of $-151~\mathrm{km~s^{-1}}$, the pulsar's trajectory (red line) crossed CWNU 45 about 0.86 Myr ago (solid line) and reached the region of Collinder 132 about 1.17 Myr ago (dashed line). The black dashed circle shows the $3r_{50}$ extent of CWNU 45.
• Figure 3: Distributions of minimum separations $\Delta_{\text{min}}$ and corresponding encounter times $\tau$ for PSR J0630$-$2834 and Collinder 132, with an encounter time of $1.6^{+0.4}_{-0.3}$ Myr. The solid red curve is the theoretically expected distribution of $\Delta_{\text{min}}$ (\ref{['eq:2']}), while the color bar indicates the probability of each pixel.
• Figure 4: The sky location of PSR J1302$-$6350, two open clusters (UBC 525 and HSC 2546), the stellar association Cen OB1 and their member stars. The magenta and green dashed ellipses mark the $3r_{50}$ regions of UBC 525 and HSC 2546, respectively, with their member stars shown as dots. The gray dashed ellipse indicates the region of Cen OB1 with a radius of $3^\circ$, and the gray triangles denote its member stars CO13.
• Figure 5: Properties of the member stars of UBC 525 and the binary system PSR J1302$-$6350/LS 2883. In all panels, the color of the dot points indicates the probability of cluster membership (as defined in the colorbar); the black (red) star marks PSR J1302$-$6350 (LS 2883). In the upper-right panel, the pulsar proper motion was measured in MDS+18. The lower-left panel shows parallax versus G magnitude, with the black and red stars indicating the parallax ranges of LS 2883 using Gaia DR2 JKC+18 and DR3, respectively. The lower-right panel shows the color-magnitude diagram using Gaia DR3's photometric bands. All data are taken from Gaia DR3 unless otherwise specified.