Proper motion, spectra, and timing of PSR J1813–1749 using Chandra and NICER

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 μRA=(−0.067±0.010)arcsecyr−1 and μDec.=(−0.014±0.007)arcsecyr−1 and velocity v⊥≈900−1600kms−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 NH=(13.1±0.9)×1022cm−2⁠, photon index Γ = 1.5 ± 0.1, and 0.3–10 keV luminosity LX≈5.4×1034ergs−1(d/ 5 kpc)2 for the PWN and Γ = 1.2 ± 0.1 and LX≈9.3×1033ergs−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 ν˙=(−6.428±0.003)×10−11Hzs−1⁠. We also fit ν measurements from 2009 to 2012 and our 2019 value and find a long-term spin-down rate ν˙=(−6.3445±0.0004)×10−11Hzs−1⁠. We speculate that the difference in spin-down rates is due to glitch activity or emission mode switching.