10/25 lunch talk: Shocks in Unexpected Places

in Uncategorized
October 24th, 2013

Shocks in Unexpected Places

Georgiana Ogrean
University of Hamburg, Germany

Friday, 10/25
12:30 pm
Room CAS 500


Radio relics are Mpc-scaled, steep-spectrum synchrotron sources in the periphery of galaxy clusters, which are most likely produced by particle acceleration at merger shock waves. Two spectacular examples of relics are in the merging galaxy clusters CIZA J2242.8+5301 and 1RXS J0603.3+4214. Radio observations of the two clusters predict that the relics trace shock fronts with Mach numbers of ~4, under the assumptions of standard diffusive shock acceleration. We tested this prediction using deep XMM-Newton, Chandra, and Suzaku observations. Contrary to the expectations, a shock front of Mach number ~2.5 is present at the relic in CIZA J2242.8+5301, significantly weaker than predicted from the radio. Puzzlingly, there are also weaker inner shocks that have no corresponding radio emission. These shocks could be the consequence of violent relaxation of the dark matter cores of the clusters involved in the merger. Similarly to the case in CIZA J2242.8+5301, the Mach number we measure in X-ray at the radio relic in 1RXS J0603.3+4214 is also only ~2, significantly smaller than predicted by radio observations.

Moreover, the shock is spatially offset from the relic. I will detail these surprising results, and discuss their implications on our understanding of particle acceleration at merger shocks.