Diffuse, Nonthermal X-Ray Emission from the Galactic Star Cluster Westerlund 1

Muno, Michael P.; Law, Casey; Clark, J. Simon; Dougherty, Sean M.; De Grijs, Richard; Portegies Zwart, Simon and Yusef-Zadeh, Farhad (2006). Diffuse, Nonthermal X-Ray Emission from the Galactic Star Cluster Westerlund 1. Astrophysical Journal, 650(1) pp. 203–211.

DOI: https://doi.org/10.1086/507175

Abstract

We present the diffuse X-ray emission identified in Chandra observations of the young, massive Galactic star cluster Westerlund 1. After removing pointlike X-ray sources down to a completeness limit of ≈ ergs s−1, we identify ergs s−1 (2–8 keV) of diffuse emission. The spatial distribution of the emission can be described as a slightly elliptical Lorentzian core with a half-width at half-maximum along the major axis of , similar to the distribution of point sources in the cluster, plus a 5 halo of extended emission. The spectrum of the diffuse emission is dominated by a hard continuum component that can be described as a keV thermal plasma that has a low iron abundance (0.3 solar) or as nonthermal emission that could be stellar light that is inverse Compton scattered by MeV electrons. Only 5% of the flux is produced by a keV plasma. The low luminosity of the thermal emission and the lack of a 6.7 keV iron line suggest that 40,000 unresolved stars with masses between 0.3 and 2 M are present in the cluster, fewer than previously estimated. Moreover, the flux in the diffuse emission is a factor of several lower than would be expected from a supersonically expanding cluster wind, and there is no evidence for thermal remnants produced by supernovae. Less than 10−5 of the mechanical luminosity of the cluster is dissipated as 2–8 keV X-rays, leaving a large amount of energy that either is radiated at other wavelengths, is dissipated beyond the bounds of our image, or escapes into the intergalactic medium.

Viewing alternatives

Look up in Google Scholar

Metrics

Public Attention

Altmetrics from Altmetric

Number of Citations

Citations from Dimensions
No digital document available to download for this item

Item Actions

Export

About

CORE (COnnecting REpositories)

Recommendations