Chandra Monitoring of the J1809-1917 Pulsar Wind Nebula and Its Field

TL;DR

This study uses extensive Chandra X-ray observations to analyze the morphology, variability, and environment of the pulsar PSR J1809-1917 and its nebula, confirming its association with the nearby TeV source HESS J1809-193.

Contribution

It provides new detailed X-ray imaging and analysis of the PWN, revealing morphological features, variability, and the pulsar's motion, and confirms the pulsar as the likely source of the TeV emission.

Findings

The compact nebula shows jet-like variability likely due to Doppler boosting.

The extended nebula aligns with the pulsar's motion and the TeV source.

A faint collimated structure suggests a misaligned outflow tracing magnetic fields.

Abstract

PSR J1809-1917 is a young ($\tau=51$ kyr) energetic ($\dot{E}=1.8\times10^{36}$ erg s$^{-1}$) radio pulsar powering an X-ray pulsar wind nebula (PWN) that exhibits morphological variability. We report on the results of a new monitoring campaign by the Chandra X-ray Observatory (CXO), carried out across 6 epochs with a $\sim$7-week cadence. The compact nebula can be interpreted as a jet-dominated outflow along the pulsar's spin axis. Its variability can be the result of Doppler boosting in the kinked jet whose shape changes with time (akin to the Vela pulsar jet). The deep X-ray image, composed of 405 ks of new and 131 ks of archival CXO data, reveals an arcminute-scale extended nebula (EN) whose axis of symmetry aligns with both the axis of the compact nebula and the direction toward the peak of the nearby TeV source HESS J1809-193. The EN's morphology and extent suggest that the pulsar is likely moving through the ambient medium at a transonic velocity. We also resolved a faint 7$'$-long nonthermal collimated structure protruding from the PWN. It is possibly another instance of a "misaligned outflow" (also known as a "kinetic jet") produced by high-energy particles escaping the PWN's confinement and tracing the interstellar magnetic field lines. Finally, taking advantage of the 536 ks exposure, we analyzed the point sources in the J1809 field and classified them using multiwavelength data. None of the classified sources in the field can reasonably be expected to produce the extended TeV flux in the region, suggesting that PSR J1809-1917 is indeed the counterpart to HESS/eHWC J1809-193.