Multi-messenger observations of double neutron stars in Galactic disk with gravitational and radio waves

We evaluate the prospects for radio follow-up of double neutron stars (DNSs) in the Galactic disk that are detectable by future space-borne gravitational-wave (GW) detectors. Using a DNS population synthesized from the LIGO-inferred merger rate and inspiral waveforms for eccentric binaries, we find the average numbers of DNSs detectable by TianQin (TQ), LISA, and a joint TQ+LISA network are 217, 368, and 429, respectively, for 4-year observations and SNR ≥ 7. Fisher-matrix forecasts for joint TQ+LISA detections show parameter accuracies reaching ΔPb/Pb ~ 10−6, sky localization ΔΩ ~ 100 deg2 (improving to ~1 deg2 at SNR ~100), Δe/e ~ 0.3, and ΔṖb/Ṗb ~ 0.02; these accuracies follow power-law scalings with SNR. We then simulate radio pulse emission for possible pulsars in these DNSs using pulsar beam geometry and empirical spin-period and luminosity distributions. For TQ+LISA-detectable DNSs, the average numbers detectable by Parkes, FAST, SKA1-Mid, and SKA-Mid are 8, 10, 43, and 87, respectively. Depending on the radio facility, the average distances of GW-detectable pulsar binaries range from ~1 to ~7 kpc. Considering radiometer and phase-jitter noise, the best timing precision can be as low as ~70 ns for MSPs, with the most probable TOA uncertainty around ~100 μs.