NuSTAR observation of the center of the Coma cluster

F. Gastaldello, D. R. Wik, S. Molendi, N. J. Westergaard, A. Hornstrup, G. Madejski, D. D. M. Ferreira, S. E. Boggs, F. E. Christensen, W. W. Craig, B. W. Grefenstette, C. J. Hailey, F. A. Harrison, K. K. Madsen, D. Stern, W. W. Zhang

Published 2014-11-06Version 1

We present the results of a 55ks NuSTAR observation of the core of the Coma cluster. The global spectrum can be explained by thermal gas emission, with a conservative 90% upper limit to non-thermal inverse Compton (IC) emission of $5.1 \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$ in a 12 arcmin $\times$ 12 arcmin field of view . The brightness of the thermal component in this central region does not allow more stringent upper limits on the IC component when compared with non-imaging instruments with much larger field of views where claims of detections have been made. Future mosaic NuSTAR observations of Coma will further address this issue. The temperature map shows a relatively uniform temperature distribution with a gradient from the hot northwest side to the cooler southeast, in agreement with previous measurements. The temperature determination is robust given the flat effective area and low background in the 3-20 keV band, making NuSTAR an ideal instrument to measure high temperatures in the ICM.