Section 47. If a prisoner, under indictment for a capital crime, pleads guilty, upon being arraigned, the court shall award sentence against him; if he does not plead guilty, the court may assign him counsel and take all other measures preparatory to a trial, which shall, subject to the Massachusetts Rules of Criminal Procedure, be held as soon after the finding of the indictment as the other official duties of the justices will admit and the circumstances of the case require.