A Compact X-ray Source in the Radio Pulsar-Wind Nebula G141.2+5.0

Abstract

We report the results of a 50 ks Chandra observation of the recently discovered radio object G141.2+5.0, presumed to be a pulsar-wind nebula. We find a moderately bright unresolved X-ray source which we designate CXOU J033712.8 615302 coincident with the central peak radio emission. An absorbed power-law fit to the 241 counts describes the data well, with absorbing column $N_H = 6.7 (4.0, 9.7) \times 10^{21}$ cm$^{-2}$ and photon index $\Gamma = 1.8 (1.4, 2.2)$. For a distance of 4 kpc, the unabsorbed luminosity between 0.5 and 8 keV is $ 1.7^{+0.4}_{-0.3} \times 10^{32}$ erg s$^{-1}$ (90\% confidence intervals). Both $L_X$ and $\Gamma$ are quite typical of pulsars in PWNe. No extended emission is seen; we estimate a conservative $3 \sigma$ upper limit to the surface brightness of any X-ray PWN near the point source to be $3 \times 10^{-17}$ erg cm$^{-2}$ s$^{-1}$ arcsec$^{-2}$ between 0.5 and 8 keV, assuming the same spectrum as the point source; for a nebula of diameter $13"$, the flux limit is 6\% of the flux of the point source. The steep radio spectrum of the PWN ($\alpha \sim -0.7$), if continued to the X-ray without a break, predicts $L_X\ \rm{(nebula)} \sim 1 \times 10^{33}$ erg s$^{-1}$, so additional spectral steepening between radio and X-rays is required, as is true of all known PWNe. The high Galactic latitude gives a $z$-distance of 350 pc above the Galactic plane, quite unusual for a Population I object.