X-ray detection of the substellar twin 2MASS J11011926-7732383 AB

TL;DR

This study uses X-ray observations to analyze the emission properties of a rare wide-separation brown dwarf binary, revealing variability and a decline in X-ray luminosity with decreasing mass, and identifying the coolest X-ray emitting brown dwarf in Cha I.

Contribution

First detailed X-ray analysis of the substellar binary 2M1101AB, showing component-specific emission and variability, and expanding knowledge of brown dwarf X-ray properties in star-forming regions.

Findings

X-ray emission is primarily associated with the cooler component B.

X-ray luminosity declines with decreasing mass among Cha I members.

2M1101B is the coolest and least massive brown dwarf in Cha I detected in X-rays.

Abstract

2MASS J11011926-7732383 AB (hereafter 2M1101AB), located in the Cha I star forming region, is a rare wide-separation brown dwarf binary. XMM-Newton and Chandra observations of 2M1101AB have allowed us to examine the influence of physical parameters (mass, bolometric luminosity and effective temperature) on X-ray emission from a coeval pair of substellar objects. The spatial resolution of XMM-Newton is not sufficient to separate contributions from the two components in the binary. The X-ray source detected with XMM-Newton has a column density compatible with the infrared extinction of component A. On the other hand, the binary is resolved with Chandra, and the bulk of the X-ray emission is clearly associated with the photospherically cooler component B. These apparently contradictory results point at strong variability of 2M1101's X-ray emission. Combined with previous sensitive X-ray observations from low-mass members of ChaI, we find a decline of X-ray luminosity with decreasing (sub)stellar mass that is typical for star forming regions. 2M1101B is the coolest (spectral type M8.25) and least massive brown dwarf of ChaI detected in X-rays so far. It is also among the youngest (~1 Myr) substellar ChaI members, and therefore relatively luminous. Most bona fide brown dwarfs of Cha I have remained below the sensitivity limits of available X-ray observations, because of their low luminosity associated with higher age.