X-Ray Observations of the W51 Complex with Suzaku

TL;DR

This paper analyzes Suzaku X-ray observations of the W51 complex, revealing thermal plasma characteristics in W51C and diffuse hard X-ray emission in W51B, with implications for stellar winds and particle acceleration.

Contribution

It provides the first detailed Suzaku-based spectral analysis of W51C and W51B, identifying plasma states and potential origins of hard X-ray emission in the region.

Findings

W51C's soft X-ray emission is from non-equilibrium thermal plasma at ~0.7 keV.

Mg abundance in W51C is higher than solar.

Hard X-ray emission coincides with molecular clouds and may originate from stellar winds or accelerated particles.

Abstract

We present a detailed analysis of the X-ray emission from the middle-aged supernova remnant W51C and star-forming region W51B with Suzaku. The soft X-ray emission from W51C is well represented by an optically thin thermal plasma in the non-equilibrium ionization state with a temperature of $\sim$0.7 keV. The elemental abundance of Mg is significantly higher than the solar value. We find no significant feature of an over-ionized plasma in W51C. The hard X-ray emission is spatially coincident with the molecular clouds associated with W51B, overlapping with W51C. The spectrum is represented by an optically thin thermal plasma with a temperature of $\sim$5 keV or a powerlaw model with a photon index of $\sim$2.2. The emission probably has diffuse nature since its luminosity of 1$\times10^{34}$ erg s$^{-1}$ in the 0.5-10 keV band cannot be explained by the emission from point sources in this region. We discuss the possibility that the hard X-ray emission comes from stellar winds of OB stars in W51B or accelerated particles in W51C.