The Orbital-decay Test of General Relativity to the 2% Level with 6 yr VLBA Astrometry of the Double Neutron Star PSR J1537+1155

Abstract

Abstract PSR J1537+1155, also known as PSR B1534+12, is the second discovered double neutron star (DNS) binary. More than 20 yr of timing observations of PSR J1537+1155 have offered some of the most precise tests of general relativity (GR) in the strong-field regime. As one of these tests, the gravitational-wave emission predicted by GR has been probed with the significant orbital decay ( P ̇ b ) of PSR J1537+1155. However, compared to most GR tests provided with the post-Keplerian parameters, the orbital-decay test was lagging behind in terms of both precision and consistency with GR, limited by the uncertain distance of PSR J1537+1155. With an astrometric campaign spanning 6 yr using the Very Long Baseline Array, we measured an annual geometric parallax of 1.063 ± 0.075 mas for PSR J1537+1155, corresponding to a distance of 0.94 − 0.06 + 0.07 kpc. This is the most tightly constrained model-independent distance achieved for a DNS to date. After obtaining P ̇ b Gal (i.e., the orbital decay caused by Galactic gravitational potential) with a combination of four Galactic mass distribution models, we updated the ratio of the observed intrinsic orbital decay to the GR prediction to 0.977 ± 0.020, three times more precise than the previous orbital-decay test (0.91 ± 0.06) made with PSR J1537+1155.