2020MNRAS.498.4396H

PSR J1813-1749 is one of the most energetic rotation-powered pulsars known, producing a pulsar wind nebula (PWN) and gamma-ray and TeV emission, but whose spin period is only measurable in X-ray. We present analysis of two Chandra data sets that are separated by more than 10 yr and recent NICER data. The long baseline of the Chandra data allows us to derive a pulsar proper motion µ_ RA_=(-0.067±0.010) arcsecyr^–1 and µ_ Dec._=(-0.014±0.007) arcsecyr^–1 and velocity v_⊥~_900–1600km s^–1 (assuming a distance d = 3-5 kpc), although we cannot exclude a contribution to the change in measured pulsar position due to a change in brightness structure of the PWN very near the pulsar. We model the PWN and pulsar spectra using an absorbed power law and obtain best-fitting absorption N_ H_=(13.1±0.9)×10²² cm^–2, photon index Γ = 1.5 ± 0.1, and 0.3-10 keV luminosity L_ X_~5.4×10³⁴ erg s^–1(d/ 5 kpc)^2 for the PWN and Γ = 1.2 ± 0.1 and L_ X_~9.3×10³³ erg s^–1(d/ 5 kpc)^2 for PSR J1813-1749. These values do not change between the 2006 and 2016 observations. We use NICER observations from 2019 to obtain a timing model of PSR J1813-1749, with spin frequency ν = 22.35 Hz and spin frequency time derivative {dot}ν=(-6.428±0.003)×10^–11 Hz s^–1. We also fit ν measurements from 2009 to 2012 and our 2019 value and find a long-term spin-down rate {dot}ν=(-6.3445±0.0004)×10^–11 Hz s^–1. We speculate that the difference in spin-down rates is due to glitch activity or emission mode switching.