Microarcsecond VLBI Pulsar Astrometry with PSRπ II. Parallax Distances for 57 Pulsars

Abstract

We present the results of PSRπ, a large astrometric project targeting radio pulsars using the Very Long Baseline Array (VLBA). From our astrometric database of 60 pulsars, we have obtained parallaxbased distance measurements for all but 3, with a parallax precision that is typically ∼45 µas and approaches 10 µas in the best cases. Our full sample doubles the number of radio pulsars with a reliable ( 5σ) model-independent distance constraint. Importantly, many of the newly measured pulsars are well outside the solar neighborhood, and so PSRπ brings a near-tenfold increase in the number of pulsars with a reliable model-independent distance at d > 2 kpc. Our results show that both widelyused Galactic electron density distribution models contain significant shortcomings, particularly at high Galactic latitudes. When comparing our results to pulsar timing, two of the four millisecond pulsars in our sample exhibit significant discrepancies in their proper motion estimates. With additional VLBI observations that extend our sample and improve the absolute positional accuracy of our reference sources, we will be able to additionally compare pulsar absolute reference positions between VLBI and timing, which will provide a much more sensitive test of the correctness of the solar system ephemerides used for pulsar timing. Finally, we use our large sample to estimate the typical accuracy attainable for differential VLBA astrometry of pulsars, showing that for sufficiently bright targets observed 8 times over 18 months, a parallax uncertainty of 4 µas per arcminute of separation between the pulsar and calibrator can be expected.

The observed velocity distribution of young pulsars – II. Analysis of complete PSRπ

“…Despite the corrections for motion of LSR being small as it is seen from Figure 1 (red lines), we take them into account by adopting a flat Galaxy rotation curve with speed v R = 220 km s −1 and distance of the Sun from the Galactic center R = 8.5 kpc. Pulsars in the catalogue by Deller et al (2019) have smaller parallaxes in comparison to previous measurements, see left panel of Figure 2.…”

“…In this research, we combine new measurements presented by Deller et al (2019) with older reliable VLBI measurements of parallaxes and proper motions previously collected by . Table 1 shows the list of literature sources; all the measurements are compiled in the master list Table A.…”

“…In general our master list includes nearly all objects from Deller et al (2019) with exception of four millisecond (recycled) radio pulsars (J2010-1323, J2145-0750, J2317+1439 and J1022+1001). We also exclude NSWD system J0823+0159.…”

“…The total number of previous measurements of good quality is 24, while the number of new good quality measurements is 45. We do not extend our sample further to include pulsars with distances based on dispersion measure and an electron density model of the Galaxy as it was shown by Deller et al (2019) these distances could differ 3-5 times from parallax measurements both for NE2001 (Cordes & Lazio 2002) and YMW16 (Yao et al 2017) models.…”

“…The primary reason for this new study is a recent publication of a large sample of precise interferometric measurements by Deller et al (2019). This sample contains measurements for 57 radio pulsars; most parallaxes are measured for the first time.…”