On congruences mod <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msup><mml:mi mathvariant="fraktur">p</mml:mi><mml:mi>m</mml:mi></mml:msup></mml:math> between eigenforms and their attached Galois representations