The XXL Survey IV. Mass-temperature relation of the bright cluster sample

Context. The XXL Survey is the largest survey carried out by XMM-Newton. Covering an area of 50 deg(2), the survey contains similar to 450 galaxy clusters out to a redshift similar to 2 and to an X-ray flux limit of similar to 5 x 10(-1)5 erg s(-1) cm(-2). This paper is part of the first release of XXL results focussed on the bright cluster sample. Aims. We investigate the scaling relation between weak-lensing mass and X-ray temperature for the brightest clusters in XXL. The scaling relation discussed in this article is used to estimate the mass of all 100 clusters in XXL-100-GC. Methods. Based on a subsample of 38 objects that lie within the intersection of the northern XXL field and the publicly available CFHTLenS shear catalog, we derive the weak-lensing mass of each system with careful considerations of the systematics. The clusters lie at 0.1 < z < 0.6 and span a temperature range of T similar or equal to 1-5 keV. We combine our sample with an additional 58 clusters from the literature, increasing the range to T similar or equal to 1-10 keV. To date, this is the largest sample of clusters with weak-lensing mass measurements that has been used to study the mass-temperature relation. Results. The mass-temperature relation fit (M proportional to T-b) to the XXL clusters returns a slope b = 1.78(-0.32)(+0.37) and intrinsic scatter sigma(slnM| T) similar or equal to 0.53; the scatter is dominated by disturbed clusters. The fit to the combined sample of 96 clusters is in tension with self-similarity, b = 1.67 +/- 0.12 and sigma(lnM vertical bar T) similar or equal to 0.41. Conclusions. Overall our results demonstrate the feasibility of ground-based weak-lensing scaling relation studies down to cool systems of similar to 1 keV temperature and highlight that the current data and samples are a limit to our statistical precision. As such we are unable to determine whether the validity of hydrostatic equilibrium is a function of halo mass. An enlarged sample of cool systems, deeper weak-lensing data, and robust modelling of the selection function will help to explore these issues further.