NuSTAR's Hard Look at the Bullet Cluster: First Results
Abstract
Mergers between massive galaxy clusters are the most energetic events since the Big Bang, driving shocks and turbulence in the intracluster medium (ICM) that heats the gas and accelerates relativistic particles. Many disturbed clusters host radio halos, and detecting the corresponding inverse Compton (IC) emission is crucial for nailing down the average strength of the ICM magnetic field and thus the total energetics of its relativistic component. However, the lack of X-ray sensitivity at energies above 10 keV have made robust measurements of >10 keV shock temperatures and IC emission extremely challenging. At present, IC detections are of low significance and/or are controversial, primarily due to natural uncertainties in the background of non-imaging instruments. NuSTAR's unprecedented spatial resolution and sensitivity above 10 keV have reduced these uncertainties and have allowed unambiguous confirmation or rejection of previous measurements in the Bullet cluster. This cluster exhibits a luminous radio halo and potentially very hot (>15 keV) gas in a shock. We present preliminary results from two 150 ks observations of the Bullet with NuSTAR, designed to detect a putative IC component and precisely measure the temperature of the shock being driven by the bullet subcluster. Despite detections of IC emission with RXTE and Swift, we find the NuSTAR spectrum to be inconsistent with an IC component at the previously measured flux level. We also present spatially resolved, joint NuSTAR/Chandra spectral fits that constrain the temperatures of the hottest gas in the ICM, with a particular focus on the shock region.
- Publication:
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AAS/High Energy Astrophysics Division #13
- Pub Date:
- April 2013
- Bibcode:
- 2013HEAD...1340102W