Searching for Diffuse Nonthermal X-Rays from the Superbubbles N11 and N51D in the Large Magellanic Cloud

TL;DR

This study used Suzaku and XMM-Newton observations to investigate diffuse X-ray emissions in the superbubbles N11 and N51D in the Large Magellanic Cloud, finding no significant nonthermal emission contrary to previous claims.

Contribution

The paper provides the first careful upper limits on nonthermal X-ray emission from N11 and N51D, clarifying previous ambiguous detections and emphasizing the importance of accurate background estimation.

Findings

Diffuse thermal X-ray emission detected in both SBs.

No credible nonthermal X-ray emission detected from N11 and N51D.

Previous claims of nonthermal emission likely due to background misestimation.

Abstract

We report on observations of the superbubbles (SBs) N11 and N51D in the Large Magellanic Cloud (LMC) with Suzaku and XMM-Newton. The interior of both SBs exhibits diffuse X-ray emission, which is well represented by thin thermal plasma models with a temperature of 0.2-0.3keV. The presence of nonthermal emission, claimed in previous works, is much less evident in our careful investigation. The 3-sigma upper limits of 2-10keV flux are 3.6*10^{-14}ergs/cm^2/s and 4.7*10^{-14}ergs/cm^2/s for N11 and N51D, respectively. The previous claims of the detection of nonthermal emission are probably due to the inaccurate estimation of the non X-ray background. We conclude that no credible nonthermal emission has been detected from the SBs in the LMC, with the exception of 30 Dor C.