A multi-wavelength study of nearby millisecond pulsar PSR J1400\(-\)1431: improved astrometry & an optical detection of its cool white dwarf companion

In 2012, five high school students involved in the Pulsar Search Collaboratory discovered the millisecond pulsar PSR J1400\(-\)1431 and initial timing parameters were published in Rosen et al. (2013) a year later. Since then, we have obtained a phase-connected timing solution spanning five years, resolving a significant position discrepancy and measuring \(\dot{P}\), proper motion, parallax, and a monotonic slope in dispersion measure over time. Due to PSR J1400\(-\)1431's proximity and significant proper motion, we use the Shklovskii effect and other priors to determine a 95% confidence interval for PSR J1400\(-\)1431's distance, \(d=270^{+130}_{-80}\) pc. With an improved timing position, we present the first detection of the pulsar's low-mass white dwarf (WD) companion using the Goodman Spectrograph on the 4.1-m SOAR telescope. Deeper imaging suggests that it is a cool DA-type WD with \(T_{\rm eff}=3000\pm100\) K and \(R/R_\odot=(2.19\pm0.03)\times10^{-2}\,(d/270\,{\rm pc})\). We show a convincing association between PSR J1400\(-\)1431 and a \(\gamma\)-ray point source, 3FGL J1400.5\(-\)1437, but only weak (3.3-\(\sigma\)) evidence of pulsations after folding \(\gamma\)-ray photons using our radio timing model. We detect an X-ray counterpart with XMM-Newton but the measured X-ray luminosity (\(1\times10^{29}\) ergs s\(^{-1}\)) makes PSR J1400\(-\)1431 the least X-ray luminous rotation-powered millisecond pulsar (MSP) detected to date. Together, our findings present a consistent picture of a nearby (\(d\approx230\) pc) MSP in a 9.5-day orbit around a cool, \(\sim\)0.3 M\(_\odot\) WD companion, with orbital inclination, \(i\gtrsim60^\circ\).