PSR J2222−0137: I. Improved physical parameters for the system
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 more »
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NSF-PAR ID:
10321817
Journal Name:
Astronomy & Astrophysics
Volume:
654
ISSN:
0004-6361
1. ABSTRACT The Fermi Large Area Telescope gamma-ray source 3FGL J2039.6–5618 contains a periodic optical and X-ray source that was predicted to be a ‘redback’ millisecond pulsar (MSP) binary system. However, the conclusive identification required the detection of pulsations from the putative MSP. To better constrain the orbital parameters for a directed search for gamma-ray pulsations, we obtained new optical light curves in 2017 and 2018, which revealed long-term variability from the companion star. The resulting orbital parameter constraints were used to perform a targeted gamma-ray pulsation search using the Einstein@Home-distributed volunteer computing system. This search discovered pulsations with a period of 2.65 ms, confirming the source as a binary MSP now known as PSR J2039–5617. Optical light-curve modelling is complicated, and likely biased, by asymmetric heating on the companion star and long-term variability, but we find an inclination i ≳ 60°, for a low pulsar mass between $1.1\, \mathrm{M}_{\odot } \lt M_{\rm psr} \lt$ 1.6 M⊙, and a companion mass of 0.15–$0.22\, \mathrm{M}_{\odot }$, confirming the redback classification. Timing the gamma-ray pulsations also revealed significant variability in the orbital period, which we find to be consistent with quadrupole moment variations in the companion star, suggestive of convective activity. We also find thatmore »
5. ABSTRACT We report observed and derived timing parameters for three millisecond pulsars (MSPs) from observations collected with the Parkes 64-m telescope, Murriyang. The pulsars were found during reprocessing of archival survey data by Mickaliger et al. One of the new pulsars (PSR J1546–5925) has a spin period P = 7.8 ms and is isolated. The other two (PSR J0921–5202 with P = 9.7 ms and PSR J1146–6610 with P = 3.7 ms) are in binary systems around low-mass (${\gt}0.2\, {\rm M}_{\odot }$) companions. Their respective orbital periods are 38.2 and 62.8 d. While PSR J0921–5202 has a low orbital eccentricity e = 1.3 × 10−5, in keeping with many other Galactic MSPs, PSR J1146–6610 has a significantly larger eccentricity, e = 7.4 × 10−3. This makes it a likely member of a group of eccentric MSP–helium white dwarf binary systems in the Galactic disc whose formation is poorly understood. Two of the pulsars are co-located with previously unidentified point sources discovered with the Fermi satellite’s Large Area Telescope, but no γ-ray pulsations have been detected, likely due to their low spin-down powers. We also show that, particularly in terms of orbital diversity, the current sample of MSPs is far from complete and is subject to a number of selection biases.