X-ray observations of the Coma Cluster in a broad energy band with INTEGRAL, RXTE, and ROSAT observatories

TL;DR

This study combines X-ray data from INTEGRAL, RXTE, and ROSAT to analyze the Coma cluster's spectrum, revealing a primarily thermal emission with temperature variations and constraining non-thermal components and magnetic field strength.

Contribution

It provides a comprehensive broad-band X-ray analysis of the Coma cluster, including imaging, spectral modeling, and temperature mapping, with new constraints on non-thermal flux and magnetic fields.

Findings

The cluster spectrum is well fitted by a thermal plasma model at 8.2 keV.

Hard X-ray emission is marginally detected and consistent with previous observations.

The non-thermal flux is constrained to be very low, implying a magnetic field strength of at least 0.2μG.

Abstract

We present results of X-ray observations of the Coma cluster with multiple instruments over a broad energy band. Using the data from INTEGRAL, RXTE and ROSAT observatories, we find that the Coma spectrum in the 0.5-107 keV energy band can be well approximated by a thermal plasma emission model with a temperature of T=8.2 keV. INTEGRAL was used to image the cluster emission in the hard energy band. The cluster is only marginally detectable ~1.6sigma in the 44-107 keV energy band; however, the raw flux in this band is consistent with the previous results from Beppo-SAX and RXTE observatories. We can exclude with high significance that the hard-band flux reported by Beppo-SAX and RXTE could be produced by a single point source. The 20-80 keV flux of a possible non-thermal component in the cluster spectrum is (6.0+-8.8)*10**-12 ergs/cm^2/s. It is unlikely that the IC scattering of CMB photons is able to produce hard X-ray flux at these levels, unless the magnetic field strength is as low as 0.2muG. The latter value can be considered as a lower limit on the field strength in Coma. We also present a temperature map of the central part of the cluster, which shows significant variations and in particular, a hot, ~11.5 keV, region in the extension towards the subcluster infalling from the South-West.