Maximum energies of shock-accelerated electrons in Large Magellanic Cloud supernova remnants

Some supernova remnant X-ray spectra show evidence for synchrotron emission from the extension of the electron spectrum that produces radio synchrotro n emission. For any remnant, if the extrapolated radio flux exceeds the obs erved X-ray flux, thermal or nonthermal, a roll-off of the relativistic ele ctron energy distribution must occur below X-ray-emitting energies. We have studied the X-ray emission from 11 remnants in the Large Magellanic Cloud to constrain this roll-off energy. We assume that the electron distribution is a power law with an exponential cutoff at some and radiates in a unifor m E-max magnetic field. If the radio flux and spectral index are known, thi s simple model for the synchrotron contribution depends on only one paramet er that relates directly to E-max. Here we have modeled the X-ray spectra b y adding a component for thermal radiation of a Sedov blast wave to the syn chrotron model. For all 11 supernova remnants in this sample, the limits fo r E-max range between 10 and 80 (for a mean magnetic field of 10 muG). This result is similar to a study of Galactic remnants in which 13 out of 14 ob jects had limits between 20 and 80 TeV. We interpret E-max in the context o f shock acceleration theories. Better data and models should allow either f irm detections of nonthermal components or more restrictive limits on E-max .