092377

We request one 130ks XMM-Newton observation of a radio-flaring high-synchrotron-peaked BL Lac object that is affected by the so-called Doppler crisis. For this intriguing class of objects previous radio observations have typically found sub-luminal apparent jet speeds while their bright variable very-high-energy TeV gamma-ray emission and multiwavelength spectral models suggest very-high Doppler factors. We will observe such an object with the Event Horizon Telescope (EHT) as part of a triggered proposal. In order to understand the multiwavelength emission and possibly resolve the Doppler crisis for this source we request quasi-simultaneous XMM-Newton observations which will provide an independent probe of the Doppler factor by studying minute-scale variations in the X-ray light curve. [truncated! Please see actual data for full text]