Abstract
Context. The PSR J2222−0137 binary system has a set of features that make it a unique laboratory for tests of gravity theories. Aims. To fully exploit the system’s potential for these tests, we aim to improve the measurements of its physical parameters, spin and orbital orientation, and post-Keplerian parameters, which quantify the observed relativistic effects. Methods. We describe an improved analysis of archival very long baseline interferometry (VLBI) data, which uses a coordinate convention in full agreement with that used in timing. We have also obtained much improved polarimetry of the pulsar with the Five hundred meter Aperture Spherical Telescope (FAST). We provide an improved analysis of significantly extended timing datasets taken with the Effelsberg, Nançay, and Lovell radio telescopes; this also includes previous timing data from the Green Bank Telescope. Results. From the VLBI analysis, we have obtained a new estimate of the position angle of the ascending node, Ω = 189−18+19 deg (all uncertainties are 68% confidence limits), and a new reference position for the pulsar with an improved and more conservative uncertainty estimate. The FAST polarimetric results, and in particular the detection of an interpulse, yield much improved estimates for the spin geometry of the pulsar, in particular an inclination of the spin axis of the pulsar of ∼84 deg. From the timing, we obtain a new ∼1% test of general relativity (GR) from the agreement of the Shapiro delay parameters and the rate of advance of periastron. Assuming GR in a self-consistent analysis of all effects, we obtain much improved masses: 1.831(10) M⊙ for the pulsar and 1.319(4) M⊙ for the white dwarf companion; the total mass, 3.150(14) M⊙, confirms this as the most massive double degenerate binary known in the Galaxy. This analysis also yields the orbital orientation; in particular, the orbital inclination is 85.27(4) deg – indicating a close alignment between the spin of the pulsar and the orbital angular momentum – and Ω = 187.7(5.7) deg, which matches our new VLBI estimate. Finally, the timing also yields a precise measurement of the variation in the orbital period, Ṗb = 0.251(8) × 10−12 ss−1; this is consistent with the expected variation in the Doppler factor plus the orbital decay caused by the emission of gravitational waves predicted by GR. This agreement introduces stringent constraints on the emission of dipolar gravitational waves.
Highlights
PSR J2222−0137 is a pulsar with a spin period (P) of 32.8 ms, which was discovered in the Green Bank Telescope (GBT) 350 MHz drift-scan pulsar survey (Boyles et al 2013)
As we describe later in the paper, there are dispersion measure (DM) variations on relatively short timescales, which are not captured by any simple model with a few DM derivatives and are large enough to influence our measurements of parameters that have long-term time signatures, like the spin period, its derivative, the position and especially the proper motion
In this paper we present the results of a 12-year timing of PSR J2222−0137, combining data from the Effelsberg, Nançay, and Lovell radio telescopes with early GBT data
Summary
PSR J2222−0137 is a pulsar with a spin period (P) of 32.8 ms, which was discovered in the Green Bank Telescope (GBT) 350 MHz drift-scan pulsar survey (Boyles et al 2013). The edge-on orbit, the good timing precision, and the large mass of the companion allow a highly significant detection of the Shapiro delay, which was originally detected by Kaplan et al (2014) From this effect, Cognard et al (2017) obtained mp = 1.76(6) M and mc = 1.293(25) M , where M represents the solar mass parameter and the numbers in parentheses represent, as in the remainder of the work, the 68% uncertainties in the last digit. The addition of these ToAs significantly extends our timing baseline into the past, which starts on June 23, 2009, and has a length of almost 12 years This improves the precision of the measurements of proper motion, the rate of advance of periastron (ω ), and, especially, the derivative of the orbital period, Pb. we have observed the pulsar with the central beam of the 19-beam receiver of the Five hundred meter Aperture Spherical Telescope (FAST, Yao et al 2021). We can see that, for i < 90 deg, the line of sight (LOS) component of the orbital angular momentum would point towards the Earth
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