2XMM Flares Detected from Tycho-2 Stars

The flares range in duration from ~10<sup>3</sup> to ~10<sup>4</sup> s, have peak X-ray fluxes from ~10<sup>-13</sup> to ~10<sup>-11</sup> erg cm<sup>-2</sup> s<sup>-1</sup>, peak X-ray luminosities from ~10<sup>29</sup> to ~10<sup>32</sup> erg s<sup>-1</sup>, and X-ray energy output from ~10<sup>32</sup> to ~10<sup>35</sup> erg.

Most of the ~30 serendipitously-observed (target_flag = 'N') stars have little previously reported information. The hardness-ratio plots clearly illustrate the spectral (and hence inferred temperature) variations characteristic of many flares, and provide an easily accessible overview of the data. In the reference paper, the authors present flare frequency distributions from both target and serendipitous observations.

The latter provide an unbiased (with respect to stellar activity) study of flare energetics; in addition, they allow the authors to predict the numbers of stellar flares that may be detected in future X-ray wide-field surveys. The serendipitous sample demonstrates the need for care when calculating flaring rates, especially when normalizing the number of flares to a total exposure time, where it is important to consider both the stars seen to flare and those from which variability was not detected (i.e., measured as non-variable), since in the present survey, the latter outnumber the former by more than a factor of ten.

This table was created by the HEASARC in September 2015 based on the <a href="cdsarc.cds.unistra.fr/ftp/cats/J/A+A/581/A28">CDS Catalog J/A+A/581/A28</a> files tablec1.dat and tablec2.dat. This is a service provided by NASA HEASARC .