Abstract

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 mu(RA) = (-0.067 +/- 0.010) arcsec yr-1 and mu(Dec). = (-0.014 +/- 0.007) arcsec yr(-1) and velocity v(perpendicular to) approximate to 900-1600 km 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 thePWNvery near the pulsar. We model the PWNand pulsar spectra using an absorbed power law and obtain best-fitting absorption N-H = (13.1 +/- 0.9) x 10(22) cm(-2), photon index = 1.5 +/- 0.1, and 0.310 keV luminosity L-X approximate to 5.4 x 10(34) erg s(-1)( d/ 5 kpc)(2) for the PWN and Gamma = 1.2 +/- 0.1 and L-X approximate to 9.3 x 10(33) 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 nu = 22.35 Hz and spin frequency time derivative.. = (-6.428 +/- 0.003) x 10-11 Hz s-1. We also fit. measurements from 2009 to 2012 and our 2019 value and find a long-term spin-down rate (nu)over dot = (-6.3445 +/- 0.0004) x 10-11 Hz s(-1). We speculate that the difference in spin-down rates is due to glitch activity or emission mode switching.