Why the distance of PSR J0218+4232 does not challenge pulsar emission theories

Abstract

Recent very long baseline interferometry (VLBI) measurements of the astrometric parameters of the millisecond pulsar J0218+4232 by Du et al. have suggested that this pulsar is as distant as 6.3 kpc. At such a large distance, the large γ -ray flux observed from this pulsar would make it the most luminous γ -ray pulsar known. This luminosity would exceed what can be explained by the outer gap and slot-gap pulsar emission models, potentially placing important and otherwise elusive constraints on the pulsar emission mechanism. We show that the VLBI parallax measurement is dominated by the Lutz-Kelker bias. When this bias is corrected for, the most likely distance for this pulsar is 3.15+0.85-0.60 kpc. This revised distance places the luminosity of PSR J0218+4232 into a range where it does not challenge any of the standard theories of the pulsar emission mechanism.