The Orbital-decay Test of General Relativity to the 2% Level with 6 yr VLBA Astrometry of the Double Neutron Star PSR J1537+1155
Hao Ding, Adam T. Deller, Emmanuel Fonseca, Ingrid H. Stairs, Benjamin Stappers, Andrew Lyne
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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">b</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.94</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> kpc. This is the most tightly constrained model-independent distance achieved for a DNS to date. After obtaining <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">b</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>Gal</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> (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.