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Recently a large number of hot magnetic stars have been discovered to produceauroral radio emission by the process of electron cyclotron maser emission(ECME). Such stars have been given the name of Main-sequence Radio Pulseemitters (MRPs). The phenomenon characterizing MRPs is very similar to thatexhibited by planets like the Jupiter. However, one important aspect in whichthe MRPs differ from aurorae exhibited by planets is the upper cut-offfrequency of the ECME spectrum. While Jupiter's upper cut-off frequency wasfound to correspond to its maximum surface magnetic field strength, the samefor MRPs are always found to be much smaller than the frequencies correspondingto their maximum surface magnetic field strength. In this paper, we report thewideband observations (0.4--4.0 GHz) of the MRPs HD 35298 that enabled us tolocate the upper cut-off frequency of its ECME spectrum. This makes HD 35298the sixth MRP with a known constraint on the upper cut-off frequency. Withthese information, for the first time we investigate into what could lead tothe premature cut-off. We review the existing scenarios attempting to explainthis effect, and arrive at the conclusion that none of them can satisfactorilyexplain all the observations. We speculate that more than one physicalprocesses might be in play to produce the observed characteristics of ECMEcut-off for hot magnetic stars. Further observations, both for discovering morehot magnetic stars producing ECME, and to precisely locate the upper cut-off,will be critical to solve this problem.

What leads to premature upper cut-off frequencies of auroral radio emission from hot magnetic stars?