The MPIfR-MeerKAT Galactic Plane Survey II. The eccentric double neutron star system PSR J1208-5936 and a neutron star merger rate update

The MMGPS-L is the most sensitive pulsar survey in the Southern Hemisphere. We present a follow-up study of one of these new discoveries, PSR J1208-5936, a 28.71-ms recycled pulsar in a double neutron star system with an orbital period of Pb=0.632 days and an eccentricity of e=0.348. Through timing of almost one year of observations, we detected the relativistic advance of periastron (0.918(1) deg/yr), resulting in a total system mass of Mt=2.586(5) Mo. We also achieved low-significance constraints on the amplitude of the Einstein delay and Shapiro delay, in turn yielding constraints on the pulsar mass (Mp=1.26(+0.13/-0.25) Mo), the companion mass (Mc=1.32(+0.25/-0.13) Mo, and the inclination angle (i=57(2) degrees). This system is highly eccentric compared to other Galactic field double neutron stars with similar periods, possibly hinting at a larger-than-usual supernova kick during the formation of the second-born neutron star. The binary will merge within 7.2(2) Gyr due to the emission of gravitational waves. With the improved sensitivity of the MMGPS-L, we updated the Milky Way neutron star merger rate to be 25(+19/-9) Myr$^{-1}$ within 90% credible intervals, which is lower than previous studies based on known Galactic binaries owing to the lack of further detections despite the highly sensitive nature of the survey. This implies a local cosmic neutron star merger rate of 293(+222/-103} Gpc/yr, consistent with LIGO and Virgo O3 observations. With this, we predict the observation of 10(+8/-4) neutron star merger events during the LIGO-Virgo-KAGRA O4 run. We predict the uncertainties on the component masses and the inclination angle will be reduced to 5x10$^{-3}$ Mo and 0.4 degrees after two decades of timing, and that in at least a decade from now the detection of the shift in Pb and the sky proper motion will serve to make an independent constraint of the distance to the system

The MPIfR-MeerKAT Galactic Plane Survey

The MPIfR-MeerKAT Galactic Plane survey at L-band (MMGPS-L) is the most sensitive pulsar survey in the Southern Hemisphere, providing 78 discoveries in an area of 900 sq. deg. Here, we present a follow-up study of one of these new discoveries, PSR J1208−5936, a 28.71-ms recycled pulsar in a double neutron star system with an orbital period of Pb = 0.632 days and an eccentricity of e = 0.348, merging within the Hubble time. Through timing of almost one year of observations, we detected the relativistic advance of periastron (ω̇ = 0.918(1) deg yr−1), resulting in a total system mass of Mt = 2.586(5) M⊙. We also achieved low-significance constraints on the amplitude of the Einstein delay and Shapiro delay, in turn yielding constraints on the pulsar mass ($M_{\mathrm{p}}=1.26^{+0.13}_{-0.25}\,M_\odot$), the companion mass ($M_{\mathrm{c}}=1.32^{+0.25}_{-0.13}\,M_\odot$), and the inclination angle (i = 57 ± 12°). This system is highly eccentric compared to other Galactic field double neutron stars with similar periods, possibly hinting at a larger-than-usual supernova kick during the formation of the second-born neutron star. The binary will merge within 7.2(2) Gyr due to the emission of gravitational waves, making it a progenitor of the neutron star merger events seen by ground-based gravitational wave observatories. With the improved sensitivity of the MMGPS-L, we updated the Milky Way neutron star merger rate to be $\mathcal{R}_{\mathrm{MW}}^{\mathrm{new}}=25^{+19}_{-9}$ Myr−1 within 90% credible intervals, which is lower than previous studies based on known Galactic binaries owing to the lack of further detections despite the highly sensitive nature of the survey. This implies a local cosmic neutron star merger rate of $\mathcal{R}_{\mathrm{local}}^{\mathrm{new}}=293^{+222}_{-103}$ Gpc−3 yr−1, which is consistent with LIGO and Virgo O3 observations. With this, we also predict the observation of $10^{+8}_{-4}$ neutron star merger events during the LIGO-Virgo-KAGRA O4 run. We predict the uncertainties on the component masses and the inclination angle will be reduced to 5 × 10−3 M⊙ and 0.4° after two decades of timing, and that in at least a decade from now the detection of Ṗb and the sky proper motion will serve to make an independent constraint of the distance to the system