LOFAR as a Probe of the Sources of Cosmological Reionisation
  We propose use of the thickness of the ionisation front as a discriminant between alternative modes of reionisation in the early universe, by stars or by miniquasars. Assuming a photoionisation-recombination balance, we find that for miniquasar sources the transition from neutral to ionised intergalactic medium is extended and has two features. The first is a sudden steep increase in the neutral fraction with a typical width of 5-10 comoving megaparsecs, depending on the miniquasar power. The second feature is a long wing that represents a much slower transition from neutral fraction of $\approx 0.8$ to 1. The angular resolution of LOFAR is expected to resolve these scales and will, therefore, play an important role in discriminating the hard sources of ionising photons from the stellar ones. 
Saleem Zaroubi (Kapteyn Ins.) and Joseph Silk (Oxford)