Contemporaneous XMM-Newton investigation of a giant X-ray flare and quiescent state from a cool M-class dwarf in the local cavity

TL;DR

This paper reports the discovery and analysis of a giant X-ray flare from a distant M8-M8.5 dwarf star, providing new insights into stellar activity at the coolest spectral types and extending the known X-ray activity range.

Contribution

It presents the first detection of an X-ray flare from a distant M8-M8.5 dwarf, establishing its X-ray luminosity and spectral properties, and demonstrating its significance among late-type stellar sources.

Findings

X-ray flux increased by over 52 times during the flare.

The star is located at approximately 67 parsecs, making it the most distant X-ray detected object of this spectral type.

The flare's peak luminosity was about 8.2 x 10^28 erg/s, with a total energy of 2.3 x 10^32 erg.

Abstract

We report the serendipitous detection of a giant X-ray flare from the source 2XMM J043527.2-144301 during an XMM-Newton observation of the high latitude molecular cloud MBM20. The source has not been previously studied at any wavelength. The X-ray flux increases by a factor of more than 52 from quiescent state to peak of flare. A 2MASS counterpart has been identified (2MASS J04352724-1443017), and near-infrared colors reveal a spectral type of M8-M8.5 and a distance of (67\pm 13) pc, placing the source in front of MBM20. Spectral analysis and source luminosity are also consistent with this conclusion. The measured distance makes this object the most distant source (by about a factor of 4) at this spectral type detected in X-rays. The X-ray flare was characterized by peak X-ray luminosity of ~8.2E28 erg s-1 and integrated X-ray energy of ~2.3E32 erg. The flare emission has been characterized with a 2-temperature model with temperatures of ~10 and 46 MK (0.82 and 3.97 keV), and is dominated by the higher temperature component.