Chandra observations of the elusive pulsar wind nebula around PSR B0656+14

TL;DR

This study used Chandra X-ray data to detect a faint, soft, and nearly round pulsar wind nebula around PSR B0656+14, revealing insights into its structure, efficiency, and possible dust scattering effects.

Contribution

First detection of a faint, soft X-ray pulsar wind nebula around PSR B0656+14 with analysis of its properties and potential dust scattering influence.

Findings

Extended emission detected around PSR B0656+14 with low X-ray efficiency.

The nebula has a very soft spectrum, possibly dominated by dust scattering halo.

The PWN's shape and size suggest motion close to the line of sight.

Abstract

PSR B0656+14 is a middle-aged pulsar with a characteristic age $\tau_c=110$ kyr and spin-down power $\dot{E}= 3.8\times 10^{34}$ erg s$^{-1}$. Using Chandra data, we searched for a pulsar wind nebula (PWN) and found evidence of extended emission in a 3.5-15 arcsec annulus around the pulsar, with a luminosity $L_{\rm 0.5-8\,keV}^{\rm ext} \sim 8\times 10^{28}$ erg s$^{-1}$ (at the distance of 288 pc), which is a fraction of $\sim 0.05$ of the non-thermal pulsar luminosity. If the extended emission is mostly due to a PWN, its X-ray efficiency, $\eta_{\rm pwn} = L_{\rm 0.5-8\,keV}^{\rm ext}/\dot{E} \sim 2\times 10^{-6}$, is lower than those of most other known PWNe but similar to that of the middle-aged Geminga pulsar. The small radial extent and nearly round shape of the putative PWN can be explained if the pulsar is receding (or approaching) in the direction close to the line of sight. The very soft spectrum of the extended emission ($\Gamma\sim 8$), much softer than those of typical PWNe, could be explained by a contribution from a faint dust scattering halo, which may dominate in the outer part of the extended emission.