Pulsar Acceleration Mapper

Maps observed line-of-sight accelerations from TRAPUM 2026 spin-period derivatives against the maximum acceleration predicted by a central mass model. Tests whether a given IMBH mass is consistent with all 8 timed OC pulsars simultaneously.

IMBH Evidence Pulsar Timing TRAPUM 2026

Parameters

Central Mass 50,000 M☉
Mass Model
Max a from point mass: a_max = (2/3√3)·GM/r⊥²
Plummer scale radius rc 0.80 pc
OC Distance 5.49 kpc

Exclusion rule: the mass is excluded for a pulsar when amax < |aobs| (the model cannot supply the observed acceleration); amax well above aobs is the compatible case. Judged on the intrinsic-ᵢ̧-corrected aobs.
TRAPUM 90% CL: <10⁵ M☉ (formal likelihood analysis; more stringent than ratio-2 cutoff here).
Physics & citations

For a point mass M at the cluster centre, the maximum LOS acceleration at projected distance r⊥ occurs at line-of-sight depth z = r⊥/√2 and equals a_max = (2/3√3) × GM/r⊥² (the coefficient ≈ 0.3849).

The Plummer model softens the singularity by replacing r⊥² with (r⊥² + rc²), representing an extended dark cluster of scale radius rc.

The Hybrid model splits M equally between a point IMBH and a Plummer cluster, exploring the transition regime favoured by Bañares-Hernández et al. 2025.

Observed acceleration: a_obs = |ṗ / P| × c, where ṗ is the measured spin-period derivative (including intrinsic spin-down, cluster mean field, and IMBH contribution combined). Negative ṗ indicates the cluster is accelerating the pulsar toward the observer.

Verdict rule (fixed 2026-09-24, audit P0-11; the previous a_max/a_obs > 2 "tension" mapping was inverted): the mass is excluded for a pulsar when a_max < |a_obs| — the model cannot produce the observed line-of-sight acceleration even at the LOS maximum; a_max above the observation is the compatible case. Comparisons use the intrinsic-Ṗ-corrected a_obs: the measured ṗ is total (intrinsic + cluster + Shklovskii), the intrinsic term is unknown at ~10⁻²⁰ s/s, so a_obs_corr = max(|ṗ| − 10⁻²⁰, 0)/P × c. That unknown caps usable sensitivity at ~10⁻⁹–10⁻¹⁰ m/s² (Paper H pulsar-leg floor).

Data: Colom i Bernadich et al. 2026 (TRAPUM), arXiv:2603.21845
Pulsar timing: Chen et al. 2023, MNRAS 520:3847, doi:10.1093/mnras/stad029
IMBH upper limit: Bañares-Hernández et al. 2025, A&A 693:A104, doi:10.1051/0004-6361/202451763
Central mass
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Pulsars in tension
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Constraint
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amax model envelope vs. observed accelerations

Aggregate verdict
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Pulsar θ (′) P (ms) ṗ (10⁻²⁰ s/s) |a_obs| (nm/s²) a_max (nm/s²) Ratio Status
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