Vlbi Astrometry of PSR J2222-0137: A Pulsar Distance Measured to 0.4% Accuracy

Abstract

The binary pulsar J2222−0137 is an enigmatic system containing a partially recycled millisecond pulsar and a companion of unknown nature. While the low eccentricity of the system favors a white dwarf companion, an unusual double neutron star system is also a possibility, and optical observations will be able to distinguish between these possibilities. In order to allow the absolute luminosity (or upper limit) of the companion object to be properly calibrated, we undertook astrometric observations with the Very Long Baseline Array to constrain the system distance via a measurement of annual geometric parallax. With these observations, we measure the parallax of the PSR J2222-0137 system to be 3.742 . Fixing these parameters in the pulsar timing model made it possible to obtain a measurement of Shapiro delay and hence the system inclination, which shows that the system is nearly edge-on (sin i = 0.9985 ± 0.0005). Furthermore, we were able to detect the orbital motion of PSR J2222-0137 in our very long baseline interferometry (VLBI) observations and measure the longitude of ascending node Ω. The VLBI astrometry yields the most accurate distance obtained for a radio pulsar to date, and is furthermore the most accurate parallax for any radio source obtained at "low" radio frequencies (below ∼5 GHz, where the ionosphere dominates the error budget). Using the astrometric results, we show that the companion to PSR J2222-0137 will be easily detectable in deep optical observations if it is a white dwarf. Finally, we discuss the implications of this measurement for future ultra-high-precision astrometry, in particular in support of pulsar timing arrays.

MICROARCSECOND VLBI PULSAR ASTROMETRY WITH PSRπ. I. TWO BINARY MILLISECOND PULSARS WITH WHITE DWARF COMPANIONS

“…For both PSR J1022+1001 and PSR J2145-0750, a short observation (duration ∼15 minutes) was made in 2011 May to identify nearby compact radio sources that could be used as in-beam phase calibrators. The observation setup was identical to that described for the calibrator identification program in Deller et al (2013), with several short scans on pointing centers distributed around the target pulsar. From each pointing, ∼25 correlated data sets were produced centered on known radio sources located within the VLBA primary beam, using the multi-field capability of the DiFX software correlator (Deller et al 2011b).…”

“…The data reduction used was very similar to that presented in Deller et al (2013) and will be described in detail in a forthcoming p PSR catalog paper (A. T. Deller et al 2016, in preparation); we summarize it briefly here. We made use of the ParselTongue (Kettenis et al 2006) Python interface to the AIPS package (Greisen 2003, p. 109).…”

“…25; this greatly increases the precision of the differential measurements (e.g., Chatterjee et al 2009), but systematic errors often still dominate the error budget. Nevertheless, with parallax accuracy at the ∼20 μas level (Deller et al 2012(Deller et al , 2013, it is feasible to measure distances with an accuracy approaching or exceeding 1%, and in some cases it is even possible to detect the miniscule (typically 100 μas) orbital reflex motion of binary pulsars in the plane of the sky. p PSR has the goal of tripling the number of pulsars with precise, model-independent distance measurements and has now observed 60 pulsars with a wide variety of characteristics (Deller et al 2011a).…”

Radio emissions from pulsar companions: a refutable explanation for galactic transients and fast radio bursts

“…Another interesting target is the binary pulsar PSR J2222-0137, which contains a millisecond pulsar orbited by a companion of unknown nature (Deller et al 2013). As the system is seen nearly edge-on (sin i = 0.9985 ± 0.0005) and its orbital parameters are known, it is possible to observe it in search for the companion-induced signal around the transit time of the companion between the pulsar and Earth, or even to search for this signal in existing data.…”

Astrometry of OH/IR Stars Using 1612 MHz Hydroxyl Masers. I. Annual Parallaxes of WX Psc and OH138.0+7.2

“…For the systematic errors, so far, there have been two main ionospheric calibration strategies for L-band continuum astrometry: measure and remove the dispersive component of the ionospheric delays by using wide-spread bands to detect its frequency-dependent curva-ture (Brisken et al 2000(Brisken et al , 2002; or use in-beam astrometry to almost completely remove dynamic (random) and mitigate static (systematic) error terms (Chatterjee et al 2001(Chatterjee et al , 2009). Deller et al (2013Deller et al ( , 2016 demonstrated that by using in-beam calibrators with careful scheduling and data reduction, it is possible to measure parallaxes at a ∼10 µas-level precision despite the low frequency.…”