High Resolution X-ray Observations of the Pulsar Wind Nebula Associated with the Gamma-ray Source HESS$ $J1640-465

TL;DR

This study uses Chandra X-ray observations to identify a pulsar wind nebula associated with the gamma-ray source HESS J1640-465, estimating its distance, age, and pulsar properties, and discussing its asymmetric morphology.

Contribution

First detailed X-ray analysis of the PWN associated with HESS J1640-465, providing insights into its structure, distance, and pulsar characteristics, and exploring asymmetry causes.

Findings

Identification of a point source and diffuse PWN morphology.

Estimated distance between 8 and 13 kpc, age 10-30 kyr.

Derived pulsar spin-down power around 4 x 10^36 erg/s.

Abstract

We present a Chandra X-ray observation of the very high energy $\gamma$-ray source HESS$ $J1640-465. We identify a point source surrounded by a diffuse emission that fills the extended object previously detected by XMM Newton at the centroid of the HESS source, within the shell of the radio supernova remnant (SNR) G338.3-0.0. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula (PWN) and extends asymmetrically to the South-West of a point-source presented as a potential pulsar. The spectrum of the putative pulsar and compact nebula are well-characterized by an absorbed power-law model which, for a reasonable $N_{\rm H}$ value of $14\times 10^{22} \rm cm^{-2}$, exhibit an index of 1.1 and 2.5 respectively, typical of Vela-like PWNe. We demonstrate that, given the H$ $I absorption features observed along the line of sight, the SNR and the H$ $II surrounding region are probably connected and lie between 8 kpc and 13 kpc. The resulting age of the system is between 10 and 30 kyr. For a 10 kpc distance (also consistent with the X-ray absorption) the 2-10 keV X-ray luminosities of the putative pulsar and nebula are $L_{\rm PSR} \sim 1.3 \times 10^{33} d_{10 \rm kpc}^{2} \rm erg.s^{-1}$ and $L_{\rm PWN} \sim 3.9 \times 10^{33} d_{10}^{2} \rm erg.s^{-1}$ ($d_{10} = d / 10{\rm kpc}$). Both the flux ratio of $L_{\rm PWN}/L_{\rm PSR} \sim 3.4$ and the total luminosity of this system predict a pulsar spin-down power around $\dot{E} \sim 4 \times 10^{36} \rm erg s^{-1}$. We finally consider several reasons for the asymmetries observed in the PWN morphology and discuss the potential association with the HESS source in term of a time-dependent one-zone leptonic model.