Blazar Flares in Crisis at Multiwavelengths

We request one 130ks XMMNewton observation of a radioflaringhighsynchrotronpeaked BL Lac object that is affected by the socalled Dopplercrisis. For this intriguing class of objects, previous radio observations havetypically found subluminal apparent jet speeds while their bright, variable,veryhighenergy TeV gammaray emission and multiwavelength spectral modelssuggest veryhigh Doppler factors. We will observe such an object with the EventHorizon Telescope (EHT) as part of a triggered proposal. In order to understandthe multiwavelength emission and possibly resolve the Doppler crisis for thissource we request quasisimultaneous XMMNewton observations, which will providean independent probe of the Doppler factor by studying minutescale variations in the Xray light curve. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]