Below are the full references, descriptions, and processing notes for each dataset.
The ATNF Pulsar Catalogue is the definitive global database of radio pulsars, maintained by the Australia Telescope National Facility. It is queried programmatically using the psrqpy Python library, which provides direct access to the catalogue's full parameter set.
Distances are primarily derived from pulsar dispersion measures (DM) combined with models of the Galactic free electron density. Objects without distance estimates, or with distances exceeding 20 kpc, or with |z| > 5 kpc above the Galactic plane, are excluded from the visualization.
ATNF distances are always kept as published. For most pulsars in the Magellanic Clouds ATNF lists the distance of the galaxy itself (49.7 kpc for the LMC and 59.7 kpc for the SMC), so those pulsars appear on a thin surface at that distance in the 3D view. The tilted-plane model used for the Magellanic Cloud X-ray pulsars below is not applied to ATNF objects.
TYPE = AXP), which comes from McGill instead; PSR J1846-0258, which McGill lists for its 2006 magnetar-like outburst; and the LMC X-ray pulsar 1A 0535-66, taken from the LMC HMXB catalogue.
The ATNF period and period derivative of the M7 and of those three CCOs are kept and attached to their entries.
The McGill Magnetar Catalogue is the primary reference for known and candidate magnetars. It is downloaded as a CSV from the official McGill URL and processed to extract positional and distance information.
Objects are classified as magnetar, candidate magnetar (marked with # in the catalogue), or pulsar with 2006 magnetar-like outburst (marked with ##). Two extragalactic magnetars (one in the LMC and one in the SMC) are identified by angular separation from the known centers of each galaxy.
The Magnificent Seven (M7) are seven nearby, thermally-emitting, radio-quiet isolated neutron stars discovered by ROSAT. Their precise equatorial coordinates were retrieved from the SIMBAD Astronomical Database.
Distances are taken from the compilation in Table 1 of Motch et al. (2007), which lists them in parsecs (converted to kpc by dividing by 1000). For RBS 1223 the midpoint of the reported 76 to 670 pc range is used, and for RX J1605.3+3249 and RX J0420.0-5022 the published upper limits (410 and 340 pc).
Spin period and period derivative come from the ATNF catalogue. RX J1605.3+3249 is left without a period: the 6.88 s candidate listed by ATNF was not confirmed by later observations (Pires et al. 2019; Malacaria et al. 2019).
Eight of the Central Compact Objects included in this project were identified from the list curated by Andrea De Luca. Two more were added later: XMMU J173203.3-344518 in HESS J1731-347 (2.5 kpc, Doroshenko et al. 2022) and CXOU J181852.0-150213 in G15.9+0.2 (8.5 kpc, Reynolds et al. 2006). CCO coordinates were retrieved from SIMBAD, and distances are adopted from their associated supernova remnants.
CCOs are young neutron stars found at the geometric centers of supernova remnants, characterized by purely thermal X-ray emission and anomalously weak magnetic fields. Their distances are typically derived from kinematic or association-based measurements of the host remnant, carrying uncertainties of 20 to 40%.
XRBcats lists the known high-mass (169) and low-mass (349) X-ray binaries in the Galaxy. Only systems with direct evidence of a neutron star are included here: X-ray pulsations or a measured spin period, type I X-ray bursts or burst oscillations, cyclotron resonance lines, Z or atoll behaviour, a quiescent neutron star spectrum, or a radio pulsar. Black hole candidates, systems with an unknown compact object, and γ Cas analogues without detected X-ray pulsations are left out.
Systems that are already in the project under another name are not repeated. These are radio pulsars listed by ATNF (PSR B1259-63, PSR J0635+0533, and the transitional millisecond pulsars PSR J1023+0038, XSS J12270-4859, 1FGL J1417.7-4407, PSR J1723-2837 and IGR J18245-2452) and SGR 0755-2933 from McGill. Objects closer than 20 kpc and within 5 kpc of the Galactic plane are placed in the 3D view; the rest, including those without a distance estimate, appear only in The Catalog.
Only high-mass X-ray binaries with a measured neutron star spin period are included. In the SMC catalogue (148 confirmed and candidate HMXBs) that gives 54 pulsars: periods the authors flag as uncertain are dropped, as are three pulsars known only from RXTE scans whose position is uncertain by about a degree, and SMC X-3, which is already listed as a ULX pulsar. Positions are those of the optical counterpart when it is confidently identified. The SMC catalogue has no name column, so names were matched once in SIMBAD (the SXP designation closest to the measured period).
The LMC catalogue comes from the first eROSITA all-sky survey (53 confirmed and candidate HMXBs) and gives 19 pulsars, with Gaia positions of the optical counterparts. Because it is flux limited, LMC pulsars that were faint during that survey are not included. The three likely Be/white dwarf systems in it have no spin period and are not included.
These systems have no individual distance measurements. Each one is placed where its line of sight crosses the tilted plane traced by the galaxy's young stars (Classical Cepheids), centred on the mean galaxy distance. For the LMC that plane is inclined by 25° with its north-eastern side closer to us (Inno et al. 2016; mean distance 49.59 kpc, Pietrzyński et al. 2019), which spreads the pulsars over about 2 kpc in depth. For the SMC it is inclined by 74°, again with the north-eastern side closer (Haschke et al. 2012; mean distance 62.44 kpc, Graczyk et al. 2020), which spreads them over about 13 kpc. The young population of the SMC is really an elongated structure rather than a thin disk (Ripepi et al. 2017), so for the SMC the plane is an approximation of its large depth along the line of sight. Individual distances can still be off by several kpc.
Ultraluminous X-ray (ULX) pulsars: M82 X-2, NGC 7793 P13, NGC 5907 ULX1, NGC 300 ULX1, NGC 1313 X-2 and M51 ULX-7, at 2 to 17 Mpc, appear only in The Catalog, since they are far outside the 3D view. SMC X-3 and RX J0209.6-7427 in the Small Magellanic Cloud are placed in the visualizer, using the same tilted-plane model of the SMC as the Magellanic Cloud X-ray pulsars above. The listed spin period is the one at discovery; these pulsars spin up quickly, so it changes between observations.
SN 1987A compact object: JWST spectra show emission lines ionised by a compact source at the centre of the remnant, most likely a neutron star (Fransson et al. 2024). It is marked as a candidate and placed in the Large Magellanic Cloud at the distance measured for SN 1987A itself (51.4 kpc), so it does not use the plane model.