XMM X-ray spectra of Proxima Centauri

We set out to produce time-resolved XUV spectra of Prox Cen that will serve as input to atmospheric models, and to characterize the intrinsic variability of the star and its uncertainties in the inferred spectra. We analyzed the entire dataset of archival XMM-Newton observations for Prox Cen. To derive the time- resolved X-ray spectra, we implemented a new pile-up correction, a new adaptive time-binning algorithm, and a time-dependent plasma model selection.

The estimated EUV spectrum is based on a published template, that we scale with proposed relationships between X-ray and EUV fluxes. We produced spectra of Prox Cen from 1 to 920{AA} over ~260ks of observations with unprecedented time resolution. The instantaneous X-ray flux of Prox Cen varies between about 20 times and one-fifth of the average value over the available baseline, with significant differences between wavelengths.

We further quantify how variability affects the estimated average flux when a limited number of snapshots (each typically of 30 ks exposure) are available, as is common in X-ray surveys. Future investigations of the atmospheres of Prox Cen b should fold in the time variability and uncertainties described here.