XMM-Newton observations of the sigma Ori cluster. II. Spatial and spectral analysis of the full EPIC field

TL;DR

This study analyzes XMM-Newton X-ray observations of the sigma Orionis cluster, identifying sources, their properties, variability, and spectral characteristics, revealing insights into young star X-ray emission and activity.

Contribution

It provides a comprehensive spatial and spectral analysis of the full EPIC field in the sigma Orionis cluster, including new candidate members and detailed spectral properties.

Findings

Detected 175 X-ray sources, 88 with cluster membership.

Found late-type stars near the X-ray saturation limit.

Observed significant variability and flaring in ~40% of late-type stars.

Abstract

We present the results of an XMM-Newton observation of the young (~2-4 Myr) cluster around the hot star sigma Orionis. In a previous paper we presented the analysis of the RGS spectrum of the central hot star; here we discuss the results of the analysis of the full EPIC field. We have detected 175 X-ray sources, 88 of which have been identified with cluster members, including very low-mass stars down to the substellar limit. We detected eleven new possible candidate members from the 2MASS catalogue. We find that late-type stars have a median log L_X/L_bol ~ -3.3, i.e. very close to the saturation limit. We detected significant variability in ~40% of late-type members or candidates, including 10 flaring sources; rotational modulation is detected in one K-type star and possibly in another 3 or 4 stars. Spectral analysis of the brightest sources shows typical quiescent temperatures in the range T_1 ~ 0.3-0.8 keV and T_2 ~ 1-3 keV, with subsolar abundances Z ~ 0.1-0.3 Z_sun, similar to what is found in other star-forming regions and associations. We find no significant difference in the spectral properties of classical and weak-lined T Tauri stars, although classical T Tauri stars tend to be less X-ray luminous than weak-lined T Tauri stars.