A Steep spectrum radio halo in merging galaxy cluster- MACSJ0416.1-2403

Abstract

Steep Spectrum Radio Halos (RH) are very rare diffuse structures existing in the central region of merging galaxy clusters. Due to their steep spectral nature, they are often not detected at higher frequencies and tend to shine only at very low frequencies. They represent a new class of objects that could be either old halos or clusters at a special time of the merger event, when particle acceleration processes have a lower efficiency. The comparison of theoretical predictions with the low frequency observations clearly suggests that there is yet a large population of very faint RHs in galaxy clusters that still remains to be discovered with steep spectrum RHs expected to dominate this undiscovered population. As the number counts of these steep spectrum RHs is scarce, discovery of even a couple of them is important. We present result on cluster MACSJ0416.1-2403 (z = 0.396), that host one such steep spectrum RH and emphasize the important contribution of low frequency observations with interferometers like GMRT, MWA, LOFAR, SKA on cluster science and discovery of new population of rare steep spectrum RHs.