Back to Quiescence: Postoutburst Evolution of the Pulsar J1119-6127 and Its Wind Nebula

We report on the analysis of a deep Chandra observation of the high-magnetic-field pulsar (PSR) J1119-6127 and its compact pulsar wind nebula (PWN) taken in 2019 October, three years after the source went into outburst. The 0.5-7 keV postoutburst (2019) spectrum of the pulsar is best described by a two-component blackbody plus power-law model with a temperature of 0.2 ± 0.1 keV, photon index Γ = 1.8 ± 0.4, and X-ray luminosity of ${1.9}_{-0.3}^{+0.3}\times $ 10³³ erg s^-1, consistent with its preburst quiescent phase. We find that the pulsar has gone back to quiescence. The compact nebula shows a jet-like morphology elongated in the north-south direction, similar to the preburst phase. The postoutburst PWN spectrum is best fit by an absorbed power law with a photon index Γ = 2.3 ± 0.5 and a flux of ${3.2}_{-0.2}^{+0.3}$ ×10^-14 erg cm^-2 s^-1 (0.5-7 keV). The PWN spectrum shows evidence of spectral softening in the postoutburst phase, with the preburst photon index Γ = 1.2 ± 0.4 changing to Γ = 2.3 ± 0.5 and the preburst luminosity of ${1.5}_{-0.2}^{+0.3}$ × 10³² erg s^-1 changing to ${2.7}_{-0.2}^{+0.3}$ × 10³² erg s^-1 in the 0.5-7 keV band, suggesting magnetar outbursts can impact PWNe. The observed timescale for returning to quiescence, of just a few years, implies a rather fast cooling process and favors a scenario where J1119 is temporarily powered by magnetic energy following the magnetar outburst, in addition to its spin-down energy.