# {\it NuSTAR} hard X-ray studies of the pulsar wind nebula 3C~58

## TL;DR

This study uses NuSTAR and Chandra X-ray observations to analyze the energy-dependent morphology and spectra of the pulsar wind nebula 3C 58, revealing insights into electron energies and magnetic fields.

## Contribution

It provides the first detailed spatially-resolved spectral analysis of 3C 58 in hard X-rays, identifying a spectral break and constraining the nebula's magnetic field and electron energies.

## Key findings

- Size decreases with energy due to synchrotron burn-off.
- Spectral break at ~25 keV suggests maximum electron energy of ~140 TeV.
- Magnetic field strength estimated between 30-200 μG.

## Abstract

We report on new NuSTAR and archival Chandra observations of the pulsar wind nebula (PWN) 3C 58. Using the X-ray data, we measure energy-dependent morphologies and spatially-resolved spectra of the PWN. We find that the PWN size becomes smaller with increasing energy and that the spectrum is softer in outer regions. In the spatially integrated spectrum of the PWN, we find a hint of a spectral break at $\sim$25 keV. We interpret these findings using synchrotron-radiation scenarios. We attribute the size change to the synchrotron burn-off effect. The radial profile of the spectral index has a break at $R\sim80''$, implying a maximum electron energy of $\sim$200 TeV which is larger than a previous estimate, and the 25-keV spectral break corresponds to a maximum electron energy of $\sim$140 TeV for an assumed magnetic field strength of 80 $\mu$G. Combining the X-ray data and a previous radio-to-IR SED, we measure a cooling break frequency to be $\sim 10^{15}$ Hz, which constrains the magnetic-field strength in 3C 58 to be 30-200$\mu$G for an assumed age range of 800-5000 years.