Radio Proper Motions of the Energetic Pulsar PSR~J1813$-$1749

TL;DR

This study measures the radio proper motions of pulsar PSR J1813-1749 over 12 years, revealing it is not as fast as previously thought, and estimates its age to be around 1350 years, aligning with other age indicators.

Contribution

It provides refined radio proper motion measurements of PSR J1813-1749, challenging earlier claims of extremely high velocity and offering a more accurate pulsar age estimate.

Findings

Proper motion is much smaller than previous X-ray estimates.

Kinematic age of the pulsar is approximately 1350 years.

Results are consistent with the pulsar's characteristic age and supernova remnant age.

Abstract

PSR J1813--1749 has peculiarities that make it a very interesting object of study. It is one of the most energetic and the most scattered pulsar known. It is associated with HESS J1813--178, one of the brightest and most compact TeV sources in the sky. Recently, Ho et al. used archival X-ray Chandra observations separated by more than 10 years and determined that the total proper motion of PSR J1813--1749 is $\sim66$~mas~yr$^{-1}$, corresponding to a velocity of $\sim$1900 km s$^{-1}$ for a distance of 6.2 kpc. These results would imply that this pulsar is the fastest neutron star known in the Galaxy and, by estimating the angular separation with respect to the center of the associated supernova remnant, has an age of only $\sim300$ years, making it one of the youngest pulsars known. Using archival high-angular-resolution VLA observations taken over 12 years we have estimated the radio proper motions of PSR~J1813--1748 to be much smaller: ($\mu_{\alpha}\cdot\cos(\delta),\,\mu_\delta$)=($-5.0\pm3.7,\,-13.2\pm6.7$)~mas~yr$^{-1}$, or a total proper motion of $14.8\pm5.9$~mas~yr$^{-1}$. The positions referenced against quasars make our results reliable. We conclude that PSR J1813--1749 is not a very fast moving source. Its kinematic age using the new total proper motion is $\sim1350$~years. This age is consistent within a factor of a few with the characteristic age of the pulsar and with the age estimated from the broadband spectral energy distribution of HESS J1813--178, as well as the age of the associated SNR.